Wireless_Network_Administration_A_Beginner__039_s_Guide__Network_Pro_Library_

Wireless_Network_Administration_A_Beginner__039_s_Guide__Network_Pro_Library_

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Wireless Network
Administration
A Beginner’s Guide

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About the Author
Wale Soyinka is an IT systems/network/security consultant with many years of
experience in the field. He helps businesses and individuals understand, design,
deploy, secure, and integrate wireless networks. Wale is the author of the Linux
Administration: A Beginner’s Guide, now in its fifth edition.
About the Technical Editor
Craig Zacker is a writer, editor, and educator whose computing experience began in the
days of teletypes and paper tape. After moving from minicomputers to PCs, he worked
as a network administrator and desktop support technician while operating a freelance
desktop publishing business. After earning a master’s degree in English and American
Literature from New York University, Craig supported fleets of Windows workstations
and was employed as a technical writer, content provider, and webmaster for the
online services group of a large software company. Craig has authored or contributed
to dozens of books on operating systems, networking topics, and PC hardware. He has
also developed educational texts for college courses and online training courses for the
web, and he has published articles with top industry publications.

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Wireless Network
Administration
A Beginner’s Guide
Wale soyinka
New York Chicago San Francisco
Lisbon London Madrid Mexico City Milan
New Delhi San Juan Seoul Singapore Sydney Toronto

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Copyright © 2010 by The McGraw-Hill Companies. All rights reserved. Except as permitted under the United States Copyright Act of 1976, no
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Thank you Daniel A.

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At a Glance
PART I Overview
1 Regulatory and Technical Organizations  .. . . .    3
2 Wireless Communication Building Blocks  .. . .    15
3 Wireless Standards  . . . . . . . . . . . . . . . . . . . . . . . . .    29
PART II Hardware
4 Wireless Hardware: Client Side  .. . . . . . . . . . . . .    39
5 Wireless Hardware: Infrastructure Side  . . . . . .    53
PART III WLAN, WWAN, WMAN, and WPAN
6 WLAN  .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .    73
7 WWANs, WMANs, and WPANs  . . . . . . . . . . . .    89
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viii
Wireless Network Administration: A Beginner’s Guide
PART IV Protocols, Services, and Security in Wireless Networks
8 Wireless Network Services and
  Protocols: TCP/IP  .. . . . . . . . . . . . . . . . . . . . . .    107
9 Standard Wireless Network Infrastructure
  Services and Protocols: DNS, DHCP  .. . . . .    123
10 Optional Infrastructure Services
  and Protocols  . . . . . . . . . . . . . . . . . . . . . . . . . . .    141
11 Securing Wireless Networks:
  Fundamentals  .. . . . . . . . . . . . . . . . . . . . . . . . . .    151
PART V Wireless Devices Configuration and Other Wireless
Network Considerations
12 Infrastructure Device Configuration  .. . . . . . .    179
13 Microsoft Windows Clients  . . . . . . . . . . . . . . . .    197
14 Apple OS X Clients  .. . . . . . . . . . . . . . . . . . . . . . .    217
15 Linux Clients  .. . . . . . . . . . . . . . . . . . . . . . . . . . . . .    235
16 Plan, Design, Survey, and Deploy  . . . . . . . . . .    267
A Troubleshooting Wireless Networks  . . . . . . . .    283
Index  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .    305

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Contents
Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .   xvii
Introduction  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xix
Part I
Overview
1 Regulatory and Technical Organizations  .. . . . . . . . . . . . .    3
Regulatory Organizations  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .    5
The ITU-R  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .    7
Federal Communications Commission (FCC)  .. . . . . . . . . . .    8
Office of Communications (Ofcom)  . . . . . . . . . . . . . . . . . . .    9
Australian Communications and Media
  Authority (ACMA)  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .    9
Telecom Regulatory Authority of India (TRAI)  .. . . . . . . . . .    9
Canadian Radio-television and Telecommunications
  Commission (CRTC)  . . . . . . . . . . . . . . . . . . . . . . . . . . . . .   10
Technical Organizations  .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .   10
Institute of Electrical and Electronics Engineers (IEEE)  . . . .   10
Internet Engineering Task Force (IETF)  .. . . . . . . . . . . . . . . .   12
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x Wireless Network Administration: A Beginner’s Guide
European Telecommunications Standards
  Institute (ETSI)  .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .   13
Wi-Fi Alliance  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .   13
Summary  .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .   14
2 Wireless Communication Building Blocks  . . . . . . . . . . . .   15
Waves  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .   16
Frequency  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .   17
Wavelength  .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .   18
Amplitude  .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .   19
Phase  .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .   19
Bands  .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .   21
Channels  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .   22
Modulation  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .   22
Spread-Spectrum Modulation Techniques  . . . . . . . . . . . . . .   23
Digital Modulation Techniques  .. . . . . . . . . . . . . . . . . . . . . .   24
Analog Modulation Techniques  . . . . . . . . . . . . . . . . . . . . . .   26
Summary  .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .   27
3 Wireless Standards  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .   29
Standards  .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .   30
IEEE 802.3  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .   31
IEEE 802  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .   31
IEEE 802.11  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .   31
IEEE 802.11b  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .   32
IEEE 802.11a  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .   33
IEEE 802.11g  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .   33
IEEE 802.11n  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .   34
IEEE 802.11y  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .   35
IEEE 802.11k  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .   35
IEEE 802.11i  .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .   35
IEEE 802.15  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .   36
Summary  .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .   36
Part II
Hardware
4 Wireless Hardware: Client Side  . . . . . . . . . . . . . . . . . . . . .   39
Chipset  .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .   40
Components of a Wireless Chipset  . . . . . . . . . . . . . . . . . . . .   41
Chipset Makers  .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .   42
Client-Side Wireless Hardware  . . . . . . . . . . . . . . . . . . . . . . . . . .   43
PCI  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .   44
Mini PCI  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .   45

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Contents
xi
PCI Express Mini  .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .   45
PC Card  .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .   46
ExpressCard  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .   48
USB  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .   49
CompactFlash Cards and SDIO Cards  . . . . . . . . . . . . . . . . .   50
Miscellaneous Converters  .. . . . . . . . . . . . . . . . . . . . . . . . . .   51
Other Considerations for Choosing Wireless Hardware  . . . . . . .   51
Transmit Power (Tx Power)  . . . . . . . . . . . . . . . . . . . . . . . . .   52
Receiver Sensitivity (Rx)  . . . . . . . . . . . . . . . . . . . . . . . . . . . .   52
Summary  .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .   52
5 Wireless Hardware: Infrastructure Side  .. . . . . . . . . . . . . .   53
Antenna (Aerial)  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .   54
Antenna Concepts  .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .   55
Antenna Types  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .   59
Other Antenna Considerations  . . . . . . . . . . . . . . . . . . . . . . .   61
Wireless Access Point  .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .   62
WAP Operational Nodes  .. . . . . . . . . . . . . . . . . . . . . . . . . . .   63
When to Use a WAP  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .   65
Wireless Switches and Controllers  .. . . . . . . . . . . . . . . . . . . . . . .   65
Wireless Controller Considerations  .. . . . . . . . . . . . . . . . . . .   66
Wireless Routers: SOHO and Residential
  Wireless Gateways  .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .   67
Wireless Bridge  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .   68
Power over Ethernet  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .   69
Additional Considerations  . . . . . . . . . . . . . . . . . . . . . . . . . . . . .   69
Cost  .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .   70
Interoperability  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .   70
Summary  .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .   70
Part III
WLAN, WWAN, WMAN, and WPAN
6 WLAN  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .   73
WLAN Components and Concepts  .. . . . . . . . . . . . . . . . . . . . . .   74
Wireless Medium  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .   74
Wireless Station  .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .   74
Distribution System  .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .   75
Access Point   .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .   76
Basic Service Set  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .   76
Service Set ID   . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .   78
Basic Service Set ID  .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .   78
Basic Service Area   . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .   79
Extended Service Set   . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .   79

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Wireless Network Administration: A Beginner’s Guide
WLAN Standard (IEEE 802.11)  . . . . . . . . . . . . . . . . . . . . . . . . . .   79
PHY  .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .   79
MAC  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .   82
Complete MAC Frame  . . . . . . . . . . . . . . . . . . . . . . . . . . . . .   85
Summary  .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .   88
7 WWANs, WMANs, and WPANs  .. . . . . . . . . . . . . . . . . . . .   89
Wireless Wide Area Networks  .. . . . . . . . . . . . . . . . . . . . . . . . . .   90
GSM Overview  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .   90
UMTS Overview  .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .   94
LTE Overview  .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .   95
Wireless Metropolitan Area Networks  . . . . . . . . . . . . . . . . . . . . 96
WiMAX Overview  .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96
Wireless Personal Area Networks  . . . . . . . . . . . . . . . . . . . . . . . . 97
Bluetooth Overview  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98
ZigBee Overview  .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101
Summary  .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 104
Part IV
Protocols, Services, and Security in Wireless Networks
8 Wireless Network Services and Protocols: TCP/IP  . . . . . .    107
TCP/IP and UDP  .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 108
Internet Protocol  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 108
Transmission Control Protocol  . . . . . . . . . . . . . . . . . . . . . . . 111
User Datagram Protocol  . . . . . . . . . . . . . . . . . . . . . . . . . . . . 115
IP-Based Networks  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 116
Hosts and Networks  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 116
Subnetting  .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117
Netmasks  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117
IPv6  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 119
IPv6 Address Format  .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 119
IPv6 Address Types  .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 120
IPv6 Backward-Compatibility  .. . . . . . . . . . . . . . . . . . . . . . . 121
Summary  .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121
9 Standard Wireless Network Infrastructure Services
and Protocols: DNS, DHCP  . . . . . . . . . . . . . . . . . . . . . . . .    123
Domain Name System  .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 124
Domain and Host Naming Conventions  .. . . . . . . . . . . . . . . 124
The in-addr.arpa Domain  . . . . . . . . . . . . . . . . . . . . . . . . . . . 128
Types of DNS Servers  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 128
DNS Record Types  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131

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Contents xiii
DHCP  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 136
The Mechanics of DHCP  .. . . . . . . . . . . . . . . . . . . . . . . . . . . 136
DHCP Server  .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 137
DHCP Client  .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 137
DHCP Relay  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 137
Summary  .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 139
10  Optional Infrastructure Services and Protocols  .. . . . . . .    141
RADIUS  .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 142
RADIUS Entities  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 142
AAA  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 144
When to Use RADIUS  .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 146
Popular RADIUS Implementations  .. . . . . . . . . . . . . . . . . . . 147
Diameter  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 147
Diameter Entities  .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 148
Proxy Server  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 148
Types of Proxy Servers  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 149
When to Use a Proxy Server  . . . . . . . . . . . . . . . . . . . . . . . . . 150
Popular Proxy Server Implementations  . . . . . . . . . . . . . . . . 150
Summary  .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 150
11  Securing Wireless Networks: Fundamentals  . . . . . . . . . .    151
Security Background  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 152
Security Services  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 154
Cryptographic Concepts and Terms  . . . . . . . . . . . . . . . . . . . . . . 154
Plain-text  .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 154
Encryption and Decryption  .. . . . . . . . . . . . . . . . . . . . . . . . . 155
Key  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 155
Algorithm  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 157
Cipher  .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 158
Cipher Implementations  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 163
Wired Equivalent Privacy Protocol  .. . . . . . . . . . . . . . . . . . . 163
Wi-Fi Protected Access  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 164
Wi-Fi Protected Access 2 (WPA2)  . . . . . . . . . . . . . . . . . . . . . 165
EAP  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 168
EAP Entities  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 169
EAP Grammar  .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 169
EAP Types  .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 170
IEEE 802.11i  .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 172
Four-Way Handshake  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 173
IEEE 802.11i Considerations  . . . . . . . . . . . . . . . . . . . . . . . . . 173
Summary  .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 175

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Wireless Network Administration: A Beginner’s Guide
Part V
Wireless Devices Configuration and Other
Wireless Network Considerations
12  Infrastructure Device Configuration  . . . . . . . . . . . . . . . .    179
The Wireless Access Point  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 181
Configuring the WAP  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 182
The WLAN Controller  .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 186
Configuring the WLAN Controller  .. . . . . . . . . . . . . . . . . . . 187
Summary  .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 194
13  Microsoft Windows Clients  . . . . . . . . . . . . . . . . . . . . . . .    197
Windows Client Configuration  . . . . . . . . . . . . . . . . . . . . . . . . . . 198
Setting Up the Hardware  . . . . . . . . . . . . . . . . . . . . . . . . . . . 199
Setting Up a Wireless Profile  .. . . . . . . . . . . . . . . . . . . . . . . . 201
Manually Connecting to a Wireless Network  . . . . . . . . . . . . 205
netsh Utility  .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 206
Wireless Network Configuration Cloning with netsh  .. . . . . 207
Wireless Odds and Ends in Windows 7  .. . . . . . . . . . . . . . . . . . . 209
Virtual WiFi and Software Access Point  . . . . . . . . . . . . . . . . 209
Internet Connection Sharing  .. . . . . . . . . . . . . . . . . . . . . . . . 210
Summary  .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 216
14  Apple OS X Clients  .. . . . . . . . . . . . . . . . . . . . . . . . . . . . .    217
Macintosh System Design  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 218
Macintosh Software  .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 218
Macintosh Hardware  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 218
Mac OS X Wireless Client Configuration  .. . . . . . . . . . . . . . . . . . 220
Setting Up the Hardware  . . . . . . . . . . . . . . . . . . . . . . . . . . . 220
Setting Up a Wireless Location  . . . . . . . . . . . . . . . . . . . . . . . 221
Wireless Odds and Ends in OS X  .. . . . . . . . . . . . . . . . . . . . . . . . 226
Internet Sharing  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 226
Ad-Hoc Networks  .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 229
Bluetooth Dial-up Network  .. . . . . . . . . . . . . . . . . . . . . . . . . 231
Summary  .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 234
15  Linux Clients  .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .    235
Wireless Hardware on Linux Platforms  .. . . . . . . . . . . . . . . . . . . 237
Linux Wireless Drivers  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 237
Linux Wireless API  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 237
Common Linux Wireless Drivers  . . . . . . . . . . . . . . . . . . . . . 239

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Contents
xv
Wireless Network Management Tools  .. . . . . . . . . . . . . . . . . . . . 242
NetworkManager  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 242
Wireless Interface Connection Daemon  . . . . . . . . . . . . . . . . 243
ConnMan  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 243
Good Ol’ CLI  .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 243
Ubuntu Wireless Client Configuration: nm  .. . . . . . . . . . . . . . . . 249
Generic Linux Wireless Client Configuration: CLI  . . . . . . . . . . . 254
PHY and MAC Layer Configuration: CLI  .. . . . . . . . . . . . . . 254
Network and Transport Configuration: CLI  . . . . . . . . . . . . . 257
Wireless Odds and Ends in FOSS/Linux   . . . . . . . . . . . . . . . . . . 261
Ad-Hoc Networks  .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 262
Summary  .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 265
16  Plan, Design, Survey, and Deploy  . . . . . . . . . . . . . . . . . .    267
Wireless Network Planning and Designing Considerations  . . . . 268
Past, Present, and Future Hardware  . . . . . . . . . . . . . . . . . . . 268
Interoperability and Incompatibility Issues  . . . . . . . . . . . . . 269
Data Throughput  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 270
Network Reliability  .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 270
Estimating Hardware Requirements  .. . . . . . . . . . . . . . . . . . 270
Site Survey  .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 271
Site Survey Metrics  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 271
Site Survey Tools  .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 272
The Actual Site Survey  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 274
Wireless Site Deployment Examples and Considerations  . . . . . . 277
Hospitals  .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 278
Airports  .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 278
Retail Environments  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 278
High Security Areas  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 279
Home Environments  .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 280
Summary  .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 281
A  Troubleshooting Wireless Networks  .. . . . . . . . . . . . . . . .    283
Troubleshooting Regulatory and Technical
  Organization Issues  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 285
Troubleshooting Client-Side Hardware Issues  . . . . . . . . . . . . . . 285
Troubleshooting Infrastructure-Side Hardware Issues  . . . . . . . . 286
Troubleshooting Issues with the Wireless Building Blocks  . . . . . 286
Problems with Establishing Wireless Connections  . . . . . . . . . . . 289
Scanning  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 289
Selection  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 290
Authentication  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 291
Association  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 292
TCP/IP Configuration  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 292

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Wireless Network Administration: A Beginner’s Guide
Problems with Infrastructure Services and Protocols:
  TCP/IP, DNS, and DHCP Issues  . . . . . . . . . . . . . . . . . . . . . . . 293
Troubleshooting Networking Issues on Different OSs  .. . . . . . . . 294
Summary  .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 304
Index  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .    305

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Acknowledgments
To the entire McGraw-Hill production group—thank you for your patience
with my numerous missed deadlines and tardinesses. “We” did it together.
xvii

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Introduction
Wireless technologies are all around us. These technologies have pervaded
our homes, businesses, and lives. Life without some of these technologies
is almost unimaginable.
The inner workings of wireless technologies is one giant puzzle with
numerous pieces, consisting of the organizations and individuals who dream
up and conceptualize all the wonderful things that can be done wirelessly; the
companies that actualize these concepts and continually churn out cool new
products; the institutions that help to keep the wireless playing fields fair and
safe; and the end users and consumers of these technologies.
And as if this puzzle wasn’t complicated enough, individuals and companies
have come to expect (and demand) that all these components somehow “auto-
magically” connect and communicate with each other as well as with existing
wired devices. This last bit is where the wireless network administrator comes in.
Wireless Network Administration: A Beginner’s Guide provides a bird’s eye view
of the various components and technologies with which any wireless network
administrator needs to be familiar. The approach in this book is a little different
from that of other wireless network administration texts for several reasons:
This book does not attempt to prepare the reader for a wireless networking
certification exam, it does not focus solely on wireless local area networks
(WLANs), and it does not contain complex radio frequency formulae and
calculations. Instead, it has a little something for everybody and mostly provides
practical and real-world information for network and system administrators
who are tasked with understanding, designing, configuring, integrating,
supporting, and managing wireless networks.
xix

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xx
Wireless Network Administration: A Beginner’s Guide
The book contains five parts and concludes with an appendix on
troubleshooting. A mind map of the author’s vision and layout of the book
is supplied on the publisher’s web site at www.mhprofessional.com/
computingdownload.
Part I: Overview
This part of the book provides an introduction to the world of wireless technologies.
This world is governed mostly by standards (guidelines) that, among other things,
aid in ensuring interoperability among similar and countless wireless devices.
To help develop these standards, wireless technical organizations and wireless
regulatory organizations develop and help oversee and regulate the use of the
common and shared resources over which wireless communications take place.
Regulatory organizations play a key role in ensuring that everybody gets a fair
and controlled use of the air waves.
Part I also discusses the building blocks of all wireless communications. The
concepts and terms surrounding these building blocks are used in virtually all
discussions regarding anything wireless, so it is important that you understand
these concepts early on in the book.
Part II: Hardware
The standards discussed in Part I are implemented partly in the hardware. And
the regulatory bodies discussed in Part I influence how wireless networking
hardware transmits and receives wireless signals.
Part II provides an overview of hardware used in wireless networking.
Specifically, wireless hardware can be broadly grouped into client- and infrastructure-
side hardware. The categorization is based on the function and role of the hardware
in the wireless network.
Some wireless hardware is a little more difficult to categorize because it can be
found in both client- and infrastructure-side wireless hardware.
Part III: WLAN, WWAN, WMAN, and WPAN
This part delves into the numerous methods used for carrying out wireless
communications: wireless local area networks (WLANs), wireless wide area
networks (WWANs), wireless metropolitan area networks (WMANs), and
wireless personal area networks (WPANs). Which method is best is determined
by the specific application or scenario.
The influence of wireless standards is again apparent in the different wireless
networking technologies, and some of these standards are examined in greater
detail as popular technologies such as WLAN (IEEE 802.11), WWAN (GSM, LTE,
UMTS), WMAN (WiMAX), and WPAN (Bluetooth, ZigBee) are discussed.

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Introduction
xxi
Part IV: Protocols, Services, and Security in Wireless Networks
Part IV covers some protocols and services that are layered on top of the different
wireless technologies. These protocols and services work steadily in the background
of most wireless networks to make the network useful to the end user. They serve
as the glue for the networks.
Specifically, the Transmission Control Protocol/Internet Protocol (TCP/IP),
the Domain Name System (DNS), the Dynamic Host Configuration Protocol
(DHCP), authentication services, and proxy servers are covered in Part IV. The
wireless network administrator should have a good understanding of the roles,
functions, and configurations of these network elements, because they can often
make or break the entire network.
Communications over the air waves are known to be notoriously difficult to
protect. This is why after all the entities (standards, regulations, technologies,
hardware, services, and protocols) are put in place to facilitate communications
wirelessly, the next important consideration is to make sure that the communications
are secure. Part IV covers the fundamentals of securing wireless networks.
Part V: Wireless Devices Configuration and
Other Wireless Network Considerations
This part brings together everything discussed thus far into the practical world. It
begins by laying the foundation for a heterogeneous wireless network consisting
of different infrastructure hardware and different wireless clients.
These wireless infrastructure devices include wireless access points and an
enterprise grade wireless network controller/switches.
The wireless client devices include clients running the mainstream operating
systems such as Microsoft Windows, Apple OS X, and FOSS/Linux-based
systems. The nuances of the wireless networking implementations (or stacks) on
the different platforms are also covered.
You’ll also learn how to configure all the devices in a sample wireless
network.
Part V ends with a discussion of the process and importance of properly
planning, designing, and surveying the network environment before attempting
to deploy a wireless network.
Appendix
The appendix provides a quick reference for the wireless network administrator
when troubleshooting connectivity issues in a wireless network.
Your feedback is highly welcome, as future editions of this book will build on
and grow as a result of your ideas and comments. Comments can be sent to
feedback@labmanual.org.

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Part I Overview

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Chapter 1
Regulatory and Technical
Organizations
3

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4 Wireless Network Administration: A Beginner’s Guide
Key Skills and Concepts
■■ Understand the functions and necessity of wireless regulatory organizations.
■■ Identify some regulatory organizations in the wireless industry.
■■ Understand the functions and importance of technical organizations in the
wireless industry.
■■ Identify some technical organizations that impact the wireless world.
■■ Understand the standards creation process.
The wireless technology industry is a multi-billion-dollar industry. But you knew
that already.
Oddly enough, a significant factor that drives the huge growth of the wireless industry
is the consumer. I say “oddly enough” because in other technology sectors, growth and
development tend to be driven by special interest groups, hardware manufacturers,
software vendors, trade groups, standards bodies, regulatory organizations, and corporate
marketing machines. Instead of the usual technology industry trend, in which the supply
drives the demand, wireless consumers’ seemingly insatiable appetites for everything
wireless are driving the industry to push the technology and discover new frontiers.
Consumers demand and expect the latest and greatest in wireless technologies, and they
want it now.
A popular expression that states, “With great powers come great responsibilities”
can be repurposed by saying this: “With every great wireless technology comes
increased bandwidth usage as well as great responsibilities.”
Seriously speaking, the increased proliferation of, demand for, and dependence on
wireless communication systems have brought issues to the forefront that may not have
been such a big deal in the past, such as better security for wireless communications,
vastly increased radio bandwidth usage, possibility of abuse of a shared common resource
(the airwaves), and better interoperability among wireless devices. In addition, the current
balance in the wireless industry wherein the industry must constantly scramble to develop
better and faster products to please the consumers as well as fend off their competition is a
good recipe for disaster in our wireless technology–dependent world.
Enter the regulatory and technical organizations. This chapter discusses the
organizations that help manage and mediate what might otherwise be a very chaotic
wireless world. Some of these organizations control what the consumers and wireless
industry backers do with the airwaves, and others oversee the technical aspects of how
things are done over the airwaves.

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Chapter 1:  Regulatory and Technical Organizations
5
Regulatory Organizations
The airwaves over which radio communications travel is a shared natural resource.
And because it is a shared and freely occurring medium, people, countries, and
industries can choose how they make use of this resource.
Note  A medium is the material through which things propagate. Air and space are types of
mediums. Radio waves are propagated using air or space as the medium. Airwaves also refer to an
intangible medium through which radio signals can propagate.
Numerous entities exist to help enforce or encourage the sensible use of this
common resource. These entities function at international, national, and regional
levels. Regardless of the level at which they operate, the entities can be controlled by
governments, nongovernmental organizations, and profit and non-profit organizations.
Most countries have regulatory and governing bodies that manage the allocation and
use of the radio spectrum within the individual country or region. An important function
of these bodies is to help reduce or prevent interference in radio communications.
The individual regulatory bodies within each country divide the radio spectrum
into two broad groups: the licensed segment and the unlicensed segment. Only users
who are at least 18 years old can operate a wireless device in the licensed segment. The
operation of wireless devices in the licensed segment of the radio spectrum requires
a special permission (license). This license or privilege often comes at a cost. Those
younger than 18 years can operate devices using the unlicensed segment of the radio
spectrum, in which certain devices can be operated without requiring any special
licenses (permissions). Even though the segment is unlicensed, devices and users must
still adhere to certain rules that govern the use of this segment of the radio spectrum.
At an international level, bodies such as the International Telecommunication
Union Radiocommunication Sector (ITU-R) govern radio frequency (RF) usage, and
at the national or regional level, other bodies govern RF usage for the individual
nations and/or regions. Table 1-1 shows some examples of regulatory bodies that
operate at national/regional levels. The map of the world in Figure 1-1 shows the same
information. Note that the list is not all-encompassing; every country not listed here
has its own dedicated telecommunication agency whose role and function is equally
important to maintaining law and order in radio spectrum usage.
Note  The regulatory authorities of each country are often empowered by some kind of national
law and/or telecommunications act. The telecommunication act is reviewed and updated as the
telecommunications landscape of the country changes over time.
  In most countries, the intentions and design of the telecommunication laws are such that they
place the citizenry’s best interests over that of the commercial entities. But this intention is also
subject to change as the telecommunications needs and landscape changes.

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6 Wireless Network Administration: A Beginner’s Guide
Regulatory Body
Country
Comisión Nacional De Comunicaciones (CNC)
Argentina
Australian Communications and Media Authority (ACMA)
Australia
Telecom Regulatory Board (TRB)
Afghanistan
Canadian Radio-television and Telecommunications Commission (CRTC)
Canada
Autorité de Regulation des Communications Electroniques et des Postes (ARCEP) France
Telecom Regulatory Authority of India (TRAI)
India
Office of Communications (Ofcom)
United
Kingdom
Autorità per le Garanzie nelle Comunicazioni (AGCOM)
Italy
Secretaría de Comunicaciones y Transportes (SCT)
Mexico
Infocomm Development Authority of Singapore (IDA)
Singapore
Independent Communications Authority of South Africa (ICASA)
South Africa
Telecommunication Regulation Authority (TRA)
United Arab
Emirates
Nigerian Communications Commission (NCC)
Nigeria
Bundesnetzagentur (BNA)
Germany
Federal Communications Commission (FCC)
United States
Table 1-1.  National Radio Communications Regulatory Bodies
CRTC
FCC
SCT
CNC
OFCOM
BNA
ARCEP
AGCOM
NCC
TRB
TRA TRAI
IDA
ICASA
ACMA
Figure 1-1.  Map of international regulatory bodies

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Chapter 1:  Regulatory and Technical Organizations
7
The ITU-R
The United Nations and the ITU-R have at least a couple things in common: they both
have established very lofty goals within their individual focus areas and both bodies’
decisions can affect the entire world.
What the UN does for the world (facilitate cooperation in international law,
international security, economic development, social progress, human rights, achieving
world peace, and other good stuff), the ITU-R does for radio communications (help the
world avoid total anarchy and chaos that can result from the unregulated, unmanaged,
and uncoordinated use of the world’s radio spectrum).
Part of the ITU-R’s mission statement from its web site states this: “ITU-R is mandated
by its constitution to allocate spectrum and register frequency assignments, orbital
positions and other parameters of satellites, in order to avoid harmful interference between
radio stations of different countries.” (The complete text of ITU-R’s mission statement can
be found at www.itu.int/net/about/itu-r.aspx.)
ITU-R’s oversight of the world’s radio spectrum use and satellite orbit matters
affects the operation of global services such as space research, global positioning
systems (GPS), environmental monitoring, mobile communications, and other
wireless broadcasting services.
Because the world is such big place, the ITU-R has divided the world into five
administrative regions:
■■ Region A  The Americas
■■ Region B  Western Europe
■■ Region C  Eastern Europe and Northern Asia
■■ Region D  Africa
■■ Region E  E-Asia (East Asia) and Australasia
The ITU-R also categorizes the world into three radio regulatory regions, listed here
and depicted in Figure 1-2:
■■ Region 1  Europe, Middle East, Africa, the former Soviet Union including
Siberia, and Mongolia
■■ Region 2  North and South America and Pacific
■■ Region 3  Asia, Australia, and the Pacific Rim
The regulatory regions shown in Figure 1-2 are actually quite important to the
functions of a wireless network administrator. Wireless hardware manufacturers often
clearly state (in the product literature or product packaging) the regions in which their
products are designed to be operated. Buying and using wireless radio equipment
designed for use in one region (such as Region 3) and using the same equipment in
another region (such as Region 1) may constitute a punishable offense. In addition to the
legal ramifications, using radio equipment outside its designated region may also cause
technical interference with other wireless equipment and can disrupt communications.

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8 Wireless Network Administration: A Beginner’s Guide
Region 2
Region 3
Region 1
Region 3
Figure 1-2.  The ITU-R’s three radio regulatory regions
Federal Communications Commission (FCC)
The FCC set down the RF communication usage rules in the United States. This
government agency is responsible for regulating interstate and international
communications by radio, television, wire, satellite, and cable. It is responsible for
regulating the use of the radio spectrum in the United States and is empowered by
the Communications Act of 1934, which was updated in 1996 and is now referred to
as the Telecommunications Act.
The FCC has many rules, including some that affect the operation of wireless
devices. For example, a specific FCC rule allows the operation of certain wireless
network devices without a license in designated parts of the radio spectrum. This
rule can be found in a section of the FCC rules and regulation known as “Title 47
Code of Federal Regulations (CFR) Part 15.” It affects the operation of devices used in
wireless local area networks (WLANs), cordless phones, devices used in personal area
networks (PANs), to name a few. For example, the rule affects the specific frequency
ranges in which the devices can operate and the maximum amount of radio energy that
the devices can emit. The FCC is there to make sure that operators of wireless radio
equipment operate their equipment within the set FCC guidelines.
The FCC also coordinates its actions with those of other international regulatory
bodies such as the ITU-R regarding issues that might involve the use of the radio
spectrum of other countries. Consider satellite communications, for example.

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Chapter 1:  Regulatory and Technical Organizations
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The FCC acts on behalf of any local wireless operators that want to communicate
over the international airwaves. It does this by interfacing with the ITU-R and
coordinating the application process with ITU-R.
Office of Communications (Ofcom)
Ofcom establishes the radio spectrum usage rules in the United Kingdom (U.K.). It
is concerned with a wide spectrum of communications functions in the U.K.—from
managing and allocating the use of the wireless airwaves to making sure that the
people in the U.K. get the best from their communication services.
Ofcom is tasked with regulating the following communication sectors: TV and radio
broadcasts, fixed line telecoms, cellular (or mobiles), and the airwaves. Its regulations
and rules affect the operation of devices used in WLANs, cordless phones, and PAN
devices, among others. Ofcom is empowered by the Communications Act of 2003.
It is an independent regulator of communication matters—independent in the
sense that it is independent of the nation’s government. Ofcom coordinates with
other international regulatory bodies such as the ITU-R when it comes to issues that
might involve the use of the radio spectrum of other countries, such as in satellite
communications. Ofcom represents the U.K. government when dealing with ITU-R.
More complete information can be obtained about Ofcom from its web site at
www.ofcom.org.uk/. The organization is people-focused, which is apparent in its
easily comprehensible web site.
Australian Communications and Media Authority (ACMA)
ACMA is the de facto body for all matters regarding the regulation of broadcasting,
radio communications, telecommunications, and the Internet in Australia. ACMA
is responsible for planning and managing the nation’s radio spectrum usage and
handles all matters regarding compliance with licensing requirements. It investigates
complaints of interference with wireless services.
As with other regional regulatory organizations discussed thus far, ACMA also
handles all the international radio communications activities. It serves as Australia’s
representative within the ITU-R.
More detailed information about ACMA’s role can be found at its web site,
www.acma.gov.au.
Telecom Regulatory Authority of India (TRAI)
TRAI is a government-independent body that is responsible for the regulation of all
telecommunications matters in India. Among its other functions, TRAI ensures that
India’s radio spectrum is used as efficiently as possible. It is responsible for granting
licenses to wireless operators, it specifies the terms and conditions of such licenses, and
it ensures that the licensee complies with the conditions of the license.
TRAI’s mission statement, according to its web site, is “to ensure that the interests
of consumers are protected and at the same time to nurture conditions for growth of

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Wireless Network Administration: A Beginner’s Guide
telecommunications, broadcasting and cable services in a manner and at a pace which
will enable India to play a leading role in the emerging global information society.”
For more information, see TRAI’s web site at www.trai.gov.in.
Canadian Radio-television and Telecommunications Commission (CRTC)
In addition to having the coolest looking logo, CRTC is in charge of regulating all
broadcasting and telecommunications activities in Canada. CRTC departs a little
from some of the other regulatory bodies in other countries, because its role is more
administrative than technical. It defers and reports to another government institution,
Industry Canada, for certain technical matters, such as allocating radio frequencies,
radio frequency spectrum management, and radio interference.
Another interesting aspect of the CRTC is its hands-off approach to managing the
telecommunication sector in Canada. It allows the natural market forces to drive the
telecommunications market, but it uses its regulatory powers only where the market
doesn’t meet the objectives of the nation’s Telecommunications Act.
For more information, see CRTC’s web site at www.crtc.gc.ca or Industry Canada’s
web site at www.ic.gc.ca.
Technical Organizations
The focus and objectives of the technical organizations are slightly different from those
of the regulatory bodies. These technical organizations are concerned with the inner
workings and interoperability of different technologies. They define the problems or
needs and come up with solutions to address these issues.
Some of these organizations are responsible for the development and production
of numerous standards such as this one, paraphrased from the International Standards
Organization/International Electrotechnical Commission (ISO/IEC) Guide 2:2004,
definition 3.2: A standard is a document, established by consensus and approved by
a recognized body, that provides, for common and repeated use, rules, guidelines, or
characteristics for activities or their results, aimed at the achievement of the optimum
degree of order in a given context.
A standard is a set of rules that ensures quality and can be in the form of a technical
specification. Standards can be developed for processes, protocols, services, and products,
and are often regarded as guidelines; as such, compliance to standards is not mandatory.
Technical organizations that wish to be regarded as being neutral should definitely not be
in the business of enforcing compliance and adherence to the standards they create.
Institute of Electrical and Electronics Engineers (IEEE)
IEEE (pronounced “i-triple-e”) is a non-profit professional organization dedicated to the
advancement of technology. The IEEE specified standards that conform to the guidelines
established by the ITU-R, FCC, Ofcom, and other similar bodies.

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The standards formulating process of the IEEE can be a bit tedious and lengthy:
1. A project sponsor submits a Project Authorization Request (PAR) that can be
any one of the following:
■■ A new standard (such as the IEEE 802.11 standard)
■■ A revision of an existing standard (such as 802.11n, which is a revision of
the 802.11 standard)
■■ Amendments and corrigenda to an existing standard
Note  An amendment is a document that contains new material to be incorporated into an
existing standard and that may contain technical corrections to that standard as well. A corrigendum
is a document that contains only technical corrections to an existing IEEE standard.
2. Once a PAR is approved, future or ongoing work for the proposed IEEE
document is officially sanctioned. A working group (or technical committee)
is assigned to prepare and develop the document (standard). The working
group consists of individuals or organizations affected by, or interested in, the
standard.
3. Next comes the draft writing phase. The draft contains the scope, purpose, and
outline of the standard. And it is based on the PAR.
4. Ballot stage: A project or draft is ready for a sponsor ballot when it has completed
its working group development. This balloting or voting stage goes on until all
comments are resolved and a favorable majority of acceptance is reached. If a
favorable majority cannot be reached, the standard goes back to the draft stage.
5. Approval or ratification stage: Approval of an IEEE standard is achieved by
submitting the document and supporting material to the IEEE-SA Standards
Board Standards Review Committee (RevCom), which issues a recommendation
to the IEEE-SA Standards Board.
6. Publication stage: Like any good book or document, the approved standard
gets a good going over by a professional IEEE standards editor before
publication. The editor ensures that the standard is grammatically and
syntactically correct. The editor does not make any changes that affect the
technical meaning of the standard.
7. Reaffirmation stage: This is a continually ongoing process. Standards typically
are valid for a period of five years from the date of approval. During this five-
year period, amendments may need to be developed that offer revisions to
the original standard. And as a result, before the five-year period elapses, the
standard’s sponsor must initiate the reaffirmation process that affirms that the
technical content of the standard is still valid and the document is reaffirmed
for another five-year period. Updates to standards are known as amendments.

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Note  Amendments are created and standards are updated by task groups. Both the task
group and its finished document are denoted an IEEE number followed by a lowercase letter—for
example, IEEE 802.11n.
I include this outline of the intricacies of standards and the standards creation
process for a couple of reasons:
■■ The results/outcome of these standards greatly affects us as the end users
or administrator who will manage the devices that are built around these
standards. These standards directly affect the products that we see on the store
shelves.
■■ A good understanding of standards can help the wireless network administrator
make informed and timely decisions about the products used on his/her
network. The timing benefits come into play, for example, when a wireless
network administrator can properly gauge how long to wait before procuring
new wireless hardware that purports to support some future unfinished standard.
Internet Engineering Task Force (IETF)
The IETF is an open international community of technical individuals. Membership
in IETF is open to any interested individuals. IETF’s stated mission is “to make the
Internet work better by producing high quality, relevant technical documents that
influence the way people design, use and manage the Internet.”
We can infer a few things about this organization from its mission statement:
■■ The IETF is focused on Internet-related matters and technologies.
■■ The IETF has a great passion for creating and numbering documents. These
documents are referred to as Requests For Comment (RFCs), and there are
thousands upon thousands of them.
■■ The documents that the IETF creates are designed to be used by people who
build technologies or products that are used on the Internet.
■■ The IETF does not refer to itself as a “formal standards organization.” Instead,
it coyly positions itself as a body of knowledge of which “other” standard
bodies or individuals can make use in their technical processes for Internet-
related matters and technologies. It has no formal or legal authority to enforce
the standards that may result from its work.
Note  The IETF’s passion for creating and numbering documents is so deep that even its mission
statement is documented in one such document: RFC 3935. This document can be found at www
.ietf.org/rfc/rfc3935.txt.
Thanks to the volunteer work of the individuals within the IETF, standards such as
Transmission Control Protocol/Internet Protocol (TCP/IP) and Hypertext Transport

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Chapter 1:  Regulatory and Technical Organizations
13
Protocol (HTTP) have been developed. The fine work of IETF also helps indirectly influence
and promote interoperability among different Internet technology implementations.
So what, exactly, has the IETF contributed to the wireless technology world, the
impatient reader may ask? The answer is twofold:
■■ First, the importance of the IEEE in the wireless communications world has
already been established. And later on in the book, you will see some of the
important wireless standards that IEEE has created.
■■ Second, the groups at the IETF cooperate with the groups at IEEE in several
areas. As a case in point, the effect of work done within IETF can be seen
deep within some of the standards that emerge from IEEE. IETF work is used
extensively within IEEE wireless standards. Examples of such cooperation can
be found in the revised Extensible Authentication Protocol (EAP) Specification
(RFC 3748), the EAP state machine specification (RFC 4137), the IEEE 802.1x
Radius usage guidelines (RFC 3580), and the Mobile IPv6 Fast Handovers for
802.11 Networks specification (RFC 4260), just to name a few.
True to form, the IETF has created a document clarifying its relationship with the
IEEE 802 committee. This document is RFC 4441 and can be found at www.ietf.org/
rfc/rfc4441.txt.
European Telecommunications Standards Institute (ETSI)
ETSI is a European standards organization and is officially recognized and sanctioned
by the members of the European Union (EU). ETSI is a non-profit body that produces
global standards for various information and communication technologies, such
as broadcasting, medical electronics, telecommunications, and intelligent transport
systems (ITS).
At a global level, ETSI has partnerships and collaborates with other international
organizations, such as the ISO, the ITU, and the IEC. Like all good technical standards
bodies, these collaborations are meant to help create harmony between ETSI’s
standards and the standards produced by other organizations. The partnerships also
help to reduce or avoid duplication of work done by others.
ETSI been directly involved with popular standards and other technologies, such
as Digital Enhanced Cordless Telecommunications (DECT), Global System for Mobile
communication (GSM), Enhanced Data Rates for Global Evolution (EDGE), Terrestrial
Trunked Radio (TETRA), eHEALTH (healthcare informatics), and ITS, to name a few.
Wi-Fi Alliance
The Wi-Fi Alliance is a non-profit organization comprising several companies devoted
to promoting Wi-Fi technology across the globe. The Wi-Fi Alliance can be considered
a special interest group (SIG) with a goal of driving the adoption of a single worldwide
standard for high-speed wireless local area networking (LAN).

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Wireless Network Administration: A Beginner’s Guide
The focus and mission statement of the Wi-Fi Alliance is quite different from that of
the IEEE. The Wi-Fi Alliance is not exactly a standards creating entity, but it does try its
best to encourage and promote standards compliance among wireless products made
by its members. The Alliance tries to promote interoperability and quality among the
Wi-Fi products its various member companies supply. To this end, it conducts product
certifications, and any product that passes its certifications is allowed to advertise this fact.
The Wi-Fi Alliance has an ever-growing portfolio of registered trademarks, such
as Wi-Fi; Wi-Fi Multimedia (WMM); Wi-Fi Protected Access (WPA, WPA2); the Wi-Fi
CERTIFIED, Wi-Fi, and Wi-Fi ZONE logos; Wi-Fi Protected Setup. These trademarks
are intended to help boost consumers’ confidence by assuring them that any products
they buy with these logos (trademarks) will be interoperable with other products
bearing the same logos.
Summary
This chapter talked about the drivers and the odd dynamics of the wireless technology
industry—the odd dynamics being that a lot of the advancements in the industry are
driven by wireless consumers’ insatiable appetites. Consumers are forcing the suppliers
of such technologies to create faster and better products. This is a good recipe for an
industry that can quickly become unmanageable in the absence of organizations that
can be entrusted with certain oversight functions.
Several regulatory bodies help to regulate the use and allocation of the wireless
radio spectrum around the world (among other things). Some of the organizations
operate at an international level, some at a regional level, and some at a national level.
Several organizations are influential in developing the standards that drive a lot of
wireless technologies, and these standards will be discussed throughout this book. You
learned about the structures within some of the organizations, the checks and balances
within the organizations, and the standards-making process. Some organizations
have a purely non-profit motive for being in the standards game, and some non-profit
organizations participate and influence the standards development process.

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Chapter 2
Wireless Communication
Building Blocks
15

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Wireless Network Administration: A Beginner’s Guide
Key Skills and Concepts
■■ Learn the core concepts and components of wireless systems.
■■ Understand the properties of the components.
■■ Learn about modulation and demodulation techniques.
■■ Learn about analog signals and digital signals.
Your basic understanding of the building blocks upon which radio or wireless
technologies are built is useful if you plan to have any in-depth discussion on
wireless network administration. Many of the important concepts and terms
discussed in this chapter build upon one another and are dependent on one another.
Our coverage of the concepts will be kept simple and high-level for the most part.
Complex mathematical radio frequency (RF) formulae are absent.
Waves
A wave is a difficult thing to define but a simple phenomena to understand. It is difficult
because a wave can be defined in different ways, based on the specific application or
scenario. Waves are easy to understand because you can see their effects in everyday life
without having too much technical knowledge.
A wave is a type of disturbance that travels through a medium in a given time;
a transfer of energy is always associated with this travel. The medium is a tangible
or intangible thing—for example, water, air, wood, wires, or even a vacuum. Each
medium has a unique effect on how waves travel. The disturbance created by the wave
conveys useful information—the signal or data.
We can refine this definition of a wave to fit the specific focus of this book—wireless
communications. Wireless communications are conducted over radio waves. We can
therefore say that a radio wave is a disturbance that travels through air or space in
a given time.
Waves also come in different types: radio waves, sine waves, optical waves, acoustic
waves, and electromagnetic waves, to mention a few.
Electromagnetic waves are especially important in wireless communications.
They comprise electrical and magnetic components. These wave types are further
classified into different subtypes based on certain characteristics of the wave. Types of
electromagnetic waves include microwaves, infrared radiation, ultraviolet radiation,
X-rays, and finally radio waves.
In wireless communications, information is transferred by systematically changing
a characteristic of the radiated waves. Regardless of the application or context, all waves
(including radio waves) possess certain characteristics or attributes. These attributes
include amplitude, frequency, wavelength, and phase. To convey different meanings
(information or data), we simply manipulate some of these wave attributes.

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Chapter 2:  Wireless Communication Building Blocks
17
Figure 2-1.  A simple but beautiful sine wave
A sine wave, for example, is a mathematical relationship (function) that can be used
to describe smooth and repetitive movement. This movement is known as oscillation.
Conveniently for us, the attributes—amplitude, frequency, wavelength, and phase—
that we care about in radio waves can also be extrapolated unto sine waves. This is
why sine waves are so important in radio communications. Figure 2-1 shows a simple
sine wave.
These characteristics are discussed in detail in the next section.
Frequency
Frequency is a central and measurable characteristic of a wave. Generically speaking, it’s
a measure of the number of occurrences of a repeating event per fixed unit of time. The
frequency of a wave is measured in hertz (Hz). A hertz is a unit of frequency equal to
one cycle per second. It is measured according to the number of cycles per second that
occur—or the number of completed cycles per second.
Applying our definition of frequency to this unit of measurement, we could say the
following
■■ A frequency of 10 Hz means that an event repeats 10 times per second.
■■ A frequency of 1000 Hz means that an event occurs 1000 times per second.
■■ A frequency of 1 million hertz (1,000,000 Hz) means that an event repeats
1 million times per second. To avoid writing so many zeros, this can be
abbreviated as 1 MHz (one megahertz).
■■ A frequency of 1 billion hertz (1,000,000,000 Hz) means that an event repeats
1 billion times per second. This can be abbreviated as 1 GHz (one gigahertz).
■■ A frequency of 2 billion, 450 million hertz (2,450,000,000 Hz) means that an
event repeats 2.45 billion times per second. This can be abbreviated as 2.45 GHz
(2.45 gigahertz).
■■ A frequency of 1 trillion hertz (1,000,000,000,000 Hz) means that an event
repeats 1 trillion times per second. This can be abbreviated as THz (one
terahertz).
Note  Frequencies in multiples of gigahertz are very important to humans. We use the 2.45 GHz
frequency range to cook food in microwave ovens. Coincidentally, this is the same frequency range
at which radio waves used in a type of wireless local area network (WLAN) technology operate.

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Wireless Network Administration: A Beginner’s Guide
Time
Time
Time
A low frequency wave
A medium frequency wave
A high frequency wave
Figure 2-2.  Three sine waves at different frequencies relative to each other
Figure 2-2 compares the frequencies of three waveforms. The topmost sine wave
has the lowest frequency, the middle wave has a medium frequency (relative to the
other two waves), and the bottom wave has the highest frequency.
Note  Radio frequency (RF) is a specific type of frequency that forms the cornerstone of wireless
communication technologies and most of the IEEE 802.11 family of standards. It is a frequency (or
rate of oscillation) within the range of 3 Hz to 300 GHz.
Wavelength
Just as in most aspects of real life, a wave consists of successive troughs (lows) and crests
(highs). The distance between two adjacent crests or troughs is called the wavelength
(Figure 2-3). Wavelength can be measured in several ways—one crest to the next crest,
or one trough to the next trough.
Wavelength is related to frequency, and the relationship is inversely proportional—
in other words, the higher the frequency, the shorter the wavelength, and the lower the
frequency, the longer the wavelength.
Distance
Wavelength
Figure 2-3.  Wavelength
Wavelength

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19
A wavelength affects how the wave will interact with the medium in which it
travels. For example, waves with shorter wavelengths are more easily affected by solid
objects (walls, building, trees, furniture, and so on) that lie in their path. And waves
with longer wavelengths can propagate over longer distances.
Amplitude
Amplitude is a measure of the magnitude (the relative size or extent) of a wave (Figure 2-4).
It is a measure of power, strength, or height of a radio wave—the signal strength.
Amplitude is formally defined as the maximum displacement of a periodic wave.
Amplitude affects the juice remaining in a signal after traveling over a certain distance.
An RF signal transmitted with an initially higher amplitude will not necessarily travel
farther compared to a signal transmitted with an initially lower amplitude, but the signal
with the higher amplitude will be more useful when it arrives at its intended destination.
While the amplitude of a periodic wave can change as it propagates through
space, its frequency remains the same. The amplitude change can be a reduction in
the signal strength (attenuation) or an increase in the signal strength (amplification).
Various components in wireless devices are responsible for signal attenuation and
amplification. For example, wiring and connectors can cause attenuation, while an
antenna can cause amplification.
In wireless communication systems, such as WLANs, amplitude can be measured
at the transmitting end and at the receiving end of the communicating entities. At the
transmitting end, this value is called the transmit amplitude and at the receiving end it is
called the received amplitude. The wireless signal strength indicator in various wireless
devices such as cell phones and wireless cards in computers often use the received
amplitude to indicate the strength of the wireless signal to the user—to show how far
or near the user is from the source of the wireless signal (the transmitter).
Phase
This is where things start to get a bit complicated. The phase of a wave is the offset of
the wave from a reference point; it is a relative measure between two quantities—one
Amplitude
Figure 2-4.  Amplitude of a wave

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Wireless Network Administration: A Beginner’s Guide
known and the other unknown—that have something in common. When comparing
the phase relationships at a given time between two quantities, the phase of one is
usually assumed to be zero, and the phase of the second quantity is described with
respect to the first.
Here’s an attempt to untangle this convoluted definition of phase: The relationship
between the two quantities can be expressed in terms of their degrees of separation (0 to
360 degrees). Therefore, phase can also be described in terms of an angular relationship
between two waves. For example, two waves that are completely in-phase will be said to
be 0 degrees out-of-phase (or, they are simply not out-of-phase). And two waves that are
completely out-of-phase are said to be 180 degrees out-of-phase.
Phase is a subtle concept with profound influence on RF communications. In particular,
phase affects the amplitude of a wave, as you will see in the coming sections.
Phase Difference
Any two wave sources (oscillators) are said to have a phase difference if they have the
same frequency but different phases. The oscillators are then said to be out-of-phase
with each other. When that happens, the phase difference determines whether the
waves reinforce or weaken each other.
Constructive Interference  When the crest (high) of one wave passes through, or is
superimposed upon, the crest (high) of another wave, the waves are said to constructively
interfere with one another. The converse is also true: constructive interference can occur
when the trough (low) of one wave passes through or is positioned upon the trough
(low) of another wave.
So, given any two waves that are in-phase, the resulting wave or combined waves
will be stronger than either of the individual waves. This simply means a stronger
signal at the receiving end, and stronger here also means higher amplitude.
From a wireless network administrator’s perspective, most forms of constructive
interferences are beneficial to a wireless network because they can enhance wireless
communications.
Destructive Interference  When the crest (high) of one wave passes through, or is
positioned upon, the trough (low) of another wave, the waves are said to destructively
interfere with one another.
One type of destructive interference is the effect of two waves that are out-of-phase
with each other, especially when they cancel each other out. This results in a diminished
(lower amplitude) signal.
As a wireless network administrator, you almost always want to keep all forms of
destructive interference to a minimum, because they can hinder or corrupt wireless
communications.
Note  During constructive or destructive wave interference, amplitudes add or subtract depending
on whether the interaction is between the two highs or two lows or between a low and a high.

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Bands
The radio spectrum is divided into different communication frequencies called bands.
Several models exist for grouping frequencies into bands, such as the following:
■■ Medium Wave (MW) band  This band is used mainly for AM broadcasting.
In most parts of the world, the frequency range is 531–1602 kHz.
■■ Very High Frequency (VHF) band  These are the radio frequencies in the
range from 30 to 300 MHz. The common FM broadcast band is within this
range. In most parts of the world, the FM band is in the 87.5–108 MHz range,
but the FM band in Japan is 76–90 MHz.
■■ NATO K band  This band encompasses frequencies between 20 and 40 GHz.
■■ IEEE K band  This band encompasses microwave frequencies ranging from
18 to 27 GHz.
■■ Industrial, Scientific, and Medical (ISM) band  Frequencies in the ISM band
are defined by the ITU-R (see Chapter 1). Each country’s regulatory body
controls how the frequencies are used. Popular WLAN standards such as IEEE
802.11b and IEEE 802.11g operate in the ISM frequency band ranges. Table 2-1
shows the frequency ranges available in the ISM band.
Frequency Range
6.765–6.795 MHz
13.553–13.567 MHz
26.957–27.283 MHz
40.66–40.70 MHz
433.05–434.79 MHz
902–928 MHz
2.400–2.500 GHz
5.725–5.875 GHz
24–24.25 GHz
61–61.5 GHz
122–123 GHz
244–246 GHz
Table 2-1.  ISM Frequencies
Center Frequency
6.780 MHz
13.560 MHz
27.120 MHz
40.68 MHz
433.92 MHz
915 MHz
2.450 GHz
5.800 GHz
24.125 GHz
61.25 GHz
122.5 GHz
245 GHz

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Wireless Network Administration: A Beginner’s Guide
Name
UNII Low
UNII Mid
UNII Worldwide
UNII Upper
Table 2-2.  UNII Frequencies
Frequency Range
5.15–5.25 GHz
5.25–5.35 GHz
5.47–5.725 GHz
5.725–5.825 GHz
■■ Unlicensed National Information Infrastructure (UNII) band  Frequencies
and power limits in the UNII band are defined by the FCC in the United States.
This band is subdivided into frequency groups that are each 100 MHz wide.
This band is generally used for high-bandwidth applications (such as Voice
over IP, video, and so on) because of its capacity to handle such applications.
Higher bandwidth means higher data rates. The popular IEEE 802.11a WLAN
standard operates in the UNII frequency band range. See Table 2-2.
Channels
A channel in communications parlance is the route through which information is sent.
To maintain some semblance of sanity, the RF spectrum bands are divided into channels
or groups with fixed widths. Channels are usually set aside within bands for the same
purpose.
Referring to radio frequencies in terms of channels is easier than quoting actual
radio frequencies. For instance, asking a layperson to tune her television to channel 3
is easier than asking her to tune her television to the 61.25 to 65.75 MHz frequency to
receive the video and audio components of a television broadcast.
Table 2-3 shows how channels map to actual frequencies in the ISM band. These
frequencies are used in the WLAN communications that are based on the IEEE 802.11b,
IEEE 802.11g, and IEEE 802.11n standards.
Modulation
The concept of modulation is at the heart of RF communications. It is all about developing
efficient ways of massaging a signal so that it can be transmitted and properly interpreted
from one place to another over a given medium. Modulation is the process of varying
a wave pattern to use that variance to convey some kind of information. A device that
performs modulation is known as a modulator, and a device that performs the reverse
operation of modulation is known as a demodulator.

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Channel
 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
Lower Frequency (GHz)
2.401
2.404
2.411
2.416
2.421
2.426
2.431
2.436
2.441
2.451
2.451
Center Frequency (GHz)
2.412
2.417
2.422
2.427
2.432
2.437
2.442
2.447
2.452
2.457
2.462
Upper Frequency (GHz)
2.423
2.428
2.433
2.438
2.443
2.448
2.453
2.458
2.463
2.468
2.473
Table 2-3.  How Channels Map to Frequencies in the ISM Band
Several modulation schemes exist in the communications world, and in wireless
communication systems, we don’t get to choose any random modulation scheme;
instead, we have to choose the technique that best solves the problem at hand or the
technique that best suits our application. Depending on the problem or the application,
we can choose from spread-spectrum modulation techniques, digital modulation
techniques, or analog modulation techniques.
Spread-Spectrum Modulation Techniques
Spread-spectrum modulation techniques are characterized by their signature, wherein
the transmitted signal occupies more bandwidth than the actual information being
modulated. You could say that in spread-spectrum techniques, the carrier signals occur
over the full bandwidth or spectrum of the transmitting frequency. This is akin to a car
(the carrier) occupying two lanes on a highway (the medium) by driving in the middle
lane, even though all the car actually needs is one lane to transport its passengers
(information) to their destination.
Wireless applications that make use of spread-spectrum modulation are also
characterized by their ability to function at low power levels, or amplitudes.
FHSS
Frequency-hopping spread spectrum (FHSS) is a legacy spread-spectrum technology
used in RF communications. It works by transmitting data using a specific frequency
for a given length of time and then changing (hopping) to another frequency to transmit

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Wireless Network Administration: A Beginner’s Guide
more data for another fixed length of time, and this repeats ad infinitum until all the data
transfer is completed.
FHSS suffers a drawback when too many FHSS-based devices are operating within
the same area, because the probability of such devices hopping to the same frequency is
increased.
The popular wireless technology Bluetooth, used in personal area networks (PANs),
uses FHSS.
DSSS
Direct-sequence spread spectrum (DSSS) is a modulation type based on spread-spectrum
techniques. Spread-spectrum technologies deliberately transmit signals using more
frequency bandwidth than is necessary to transmit the intended information. This simply
increases the signal-to-noise ratio (SNR). DSSS implementation of spread-spectrum
adds some noise signal to the actual signal being transmitted; the extra noise is in the
form of random –1 and 1 values. Timing is very important in DSSS; the station doing
the transmitting of the data takes care of modulating the signal (adding the extra noise),
and the receiving station needs to know how to remove the extra noise from the signal to
obtain the original data.
Relative to FHSS modulation techniques, DSSS offers these advantages:
■■ Better resistance to interference
■■ Better resistance to interception
■■ Better multi-access capability (supports multiple users transmitting
simultaneously on the same frequency)
■■ Provides slightly higher data rates
■■ Shorter delays
FHSS-based systems and DSSS-based systems generally do not coexist well—that
is, one will likely interfere with the other. The interference can occur in either direction.
For example, because DSSS-based devices try to transmit on every frequency in the
band, FHSS systems might not be able to find free channels to use. Conversely, the
constant hopping between available frequencies in the band by FHSS-based systems
may starve DSSS-based systems of frequency resources.
The IEEE 802.11b WLAN standard uses the DSSS form of modulation.
Digital Modulation Techniques
Digital modulation techniques are employed when there is a need to convert digital
signals to analog signals. The converse of digital modulation would be demodulation—
the conversion of analog signals to digital form.
In the digital modulation world, there are currently three methods used to perform
this conversion, and they all depend on varying some attributes of a sine wave
representing the signal. Again, these attributes are frequency, amplitude, and phase.

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Chapter 2:  Wireless Communication Building Blocks
25
The current methods for performing digital modulation are Frequency-Shift Keying
(FSK), Amplitude-Shift Keying (ASK), and Phase-Shift Keying (PSK).
Note  In communication systems, the original information or original signal element in the system
is called the baseband. The baseband is an aspect of the system as it exists before any type of
modulation has been applied to it.
Frequency-Shift Keying
Digital-to-analog conversion of signals is achieved in FSK by changing the frequency
property of the sine wave representing the signal. As you might expect in all things
digital, two values are involved in FSK. The modulation system can choose to represent
a particular frequency with a 0 (zero) and the other frequency with a 1 (one). And by
stringing the many possible combinations of these 0’s and 1’s together, we can convey
different meanings or information signals.
OFDM  Orthogonal frequency-division multiplexing is a mouthful modulation
technique! OFDM is a digital modulation technique—specifically, an implementation
of the broader frequency-division multiplexing (FDM) techniques. FDM is a three-part
phase—frequency, division, and multiplexing—that involves dividing a frequency into
chunks (subcarriers) so that the individual chunks (or divisions) can be transmitted
individually over a single communications channel or multiplexed.
OFDM extends the basic FDM techniques by using subcarriers that are orthogonal
(or uncorrelated) to each other.
OFDM provides more efficient use of the spectrum, better resilience to severe
channel conditions, and less sensitivity to time synchronization errors between the
sender and receiver compared to in DSSS. Instead, frequency synchronization is a more
important factor in OFDM.
OFDM is widely used in numerous applications: for example, the WLAN IEEE
802.11(g)(n)(a) standards, the wireless MAN technology (WiMAX) based on IEEE 802.16,
some digital radio systems, and mobile broadband wireless access standards such as IEEE
802.20 and IEEE 802.16e.
Amplitude-Shift Keying
Digital-to-analog conversion of signals is achieved in ASK by changing the amplitude
of the wave according to changes in the information signal. The other properties of
the sine wave, such as the frequency and phase, are kept constant while the amplitude
is varied. As with all things digital, two values are involved in ASK. The modulation
system can choose to represent a particular amplitude with a 0 and another amplitude
with a 1. By stringing the many possible combinations of these 0’s and 1’s together, we
can convey different meanings or information signals.
Phase-Shift Keying
Digital-to-analog conversion of signals is achieved in PSK by changing the phase attribute
of the sine wave representing the original signal. Again, like all things digital, two values

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QAM
Hybrid modulation techniques can be created when we mix-and-match any of
our standard digital modulation methods such as PSK, ASK, and FSK. One such
modulation technique is the result of the marriage of ASK and PSK and is known
as Quadrature Amplitude Modulation (QAM). In QAM, the amplitude and phase of
the sine wave representing a signal are changed or varied in response to changes in
the data or information signal.
are involved in PSK: The modulation system can choose to represent a particular phase
with a 0 and another phase with a 1. By stringing the many possible combinations of these
0’s and 1’s together, we can convey different meanings or information signals.
Analog Modulation Techniques
Analog signals are said to be continuous and long-winded in nature. They can go on
forever if uncurtailed. Try not to be too confused when it is said that analog signals can
go on forever and then in the same breath said that analog signals have start and ending
points. Basically, this means that the possible variations within the signals themselves
can be varied and continuous.
The human voice is a good example of an analog quantity. Within any human voice
is a measurable upper and lower limit. But within these limits are numerous variations.
This is why some people scream loudly and some scream softly, some whisper quietly
and some whisper loudly, some talk normally and some talk softly, and so on. We
say that some people can change the pitch, volume, timbre, or tone of the sound they
produce. Singers especially learn how to control and manage the characteristics of the
vocal sounds they produce.
So why should the wireless network administrator care about analog signals or
digital signals? It’s simply because all things wireless are analog by nature. The wireless
transmission medium itself is analog.
Computers and other electronics often process and output information in digital
formats. If the signal information is to be used and processed only within the computer
system, it can remain and die in its digital form. But when it comes to communicating
the digital information wirelessly to other entities, the information has to be repackaged
into a form that can be transmitted using the analog wireless medium. Forget and ignore
all the books, TV shows, news media, and people that say that we are living in a digital
world. We are not: Our world is still analog. Nature is analog. The digital world we have
created is living inside our analog world.
Can you see where this is going? Enter analog modulation techniques, which are
good for transmitting analog signals over analog mediums. Here are some examples of
analog modulation methods.

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Chapter 2:  Wireless Communication Building Blocks
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Amplitude Modulation (AM)
This analog modulation technique works by varying the amplitude of the transmitted
signal relative to the information signal. A key difference between AM and its distant
cousin, ASK, is that AM does not aim to map the changes in amplitude to discrete digital
values of 0’s and 1’s. And, as such, we wouldn’t normally use AM as a modulation
technique for WLAN, wireless personal area network (WPAN), or wireless wide area
network (WWAN) communications that deal with digital and analog signals. But we
would use AM as a modulation technique for transmitting the analog human voice
signal over the analog wireless medium.
AM is not used in today’s bandwidth-hungry wireless communication systems for
several reasons. One of these reasons is that the transmitter power usage of AM is very
inefficient.
A popular implementation of AM is found in AM radio broadcasts.
Frequency Modulation (FM)
This analog modulation technique works by varying the frequency of the transmitted
signal relative to the information signal. A key difference between FM and its distant
cousin, FSK, is that FM does not aim to map the changes in frequency to discrete digital
values of 0’s and 1’s. So we wouldn’t normally use FM as a modulation technique for
WLAN communications, which deal with digital and analog signals. But we would use
FM as a modulation technique for transmitting the analog human voice signal over the
analog wireless medium.
A popular implementation of FM is found in FM radio broadcasts.
Summary
In this chapter on wireless communication building blocks, you learned the basic premise
of waves. And because waves (radio waves) are so important, some characteristics of
waves—frequency, amplitude, modulation, phase, channels, and so on—were covered.
These characteristics make up an important part of the wireless communications jargon
that we as wireless network administrators should be able to understand and speak.
You should now understand some of the methods available that rely on tweaking the
characteristics of waves to communicate some useful information signal.
This chapter also dispelled a popular myth, that we are living in a digital age.
Beyond all reasonable doubts, it was proven that we are actually living in an analog
world; the so-called digital world is living inside our analog world.

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Key Skills and Concepts
■■ Understand the importance and role of standards.
■■ Identify some popular and not-so-popular standards that define some common
wireless technologies.
Chapter 1 discussed some noteworthy organizations, including those with
regulatory functions and some with purely technical functions and objectives.
You learned how tedious and involved the standards development process can
be within the technical bodies. Surely something good should come from all that hard
work—right?
This chapter discusses some of the standards that were borne out of these organizations,
focusing on standards that impact wireless technologies in one form or another. Standards
can be moving targets that change often. This chapter covers some legacy standards,
though not in depth, with a focus on current and future standards.
Standards
As with almost every other aspect of our modern world, regulatory standards
regarding wireless use and technologies exist to guide us and act as a reference point
for interoperability, efficiency, and other aspects of wireless technologies. Remember
that standards are merely guidelines and are not binding, and as such people,
countries, and industries can choose whether or not to adhere to them.
Standards are important for several reasons, including the following:
■■ Interoperability  Standards help to promote interoperability among devices
made by different vendors. Individual vendors can build their devices to
conform to a particular standard, ensuring that their devices will be able to
work together.
■■ Efficiency  Every vendor can reuse existing solutions that a particular standard
has addressed, instead of having to re-create individual solutions. The idea is
that a standard is developed once and can be used in many instances with many
products.
■■ Prevention of vendor lock-in  Standards give technology consumers the
freedom to choose and buy whatever products they like, which helps to
reduce or prevent consumers being locked into solutions or wares provided
by particular vendors. When solutions are designed according to standards
and specifications, third-party vendors can provide continued support or
complementary solutions when an original vendor is no longer able or willing
to support its products.

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IEEE 802.3
The Institute of Electrical and Electronics Engineers (IEEE) 802.3 standard is a collection
of IEEE standards that define the properties as well as the working characteristics of
the Physical Layer and Data Link Layer’s media access control (MAC) sublayer of wired
Ethernet.
Why in the world is a standard for wired networks in a book dedicated to wireless
networks? And to make matters worse it’s right at the top of the list of the other wireless
standards that will be discussed later on.
The reason is simple. This is the standard that most wireless standards and wireless
technologies want to be like when they grow up.
IEEE 802.3 is the great granddaddy of networking protocols. It has the feel and
functionality that most wireless standards want to emulate. It represents the behavior
and nirvana that wireless network engineers would like to re-create for wireless devices.
All this is not to say or imply that IEEE 802.3 is a perfect standard or that network
engineers consider it perfect. It isn’t perfect, but it has been around for so long and
has served us so well that most agree it could be used as a basis or starting point for
defining new wireless networking standards.
Moreover, until such time when the world becomes completely cable-free (wireless),
it will be necessary for wireless devices to interoperate with their wired or cabled
siblings. And so it was deemed worthwhile that the wireless standards be designed so
that they are similar to the wired standards.
IEEE 802.3 is especially concerned with local area network (LAN) technologies,
with a nod to some wide area network (WAN) applications. And this is okay, because
the networked world is, after all, like one big LAN—that is, WANs are simply a
collection of individual LANs. So now that we have considered this little issue of
wired networking standards in a book about wireless, we can move on to the wireless
standards proper.
IEEE 802
The IEEE 802 is not a single standard—it refers to a family of standards. The committee
within IEEE that is responsible for this group of standards is known as the IEEE 802
committee, and it deals with LAN, metropolitan area network (MAN), and personal
area network (PAN) technologies and standards. It is concerned mostly with the data
link and physical layers of the Open Systems Interconnect (OSI) model.
Note  You can learn more about the work done by IEEE 802, at its web site: www.ieee802.org.
IEEE 802.11
The IEEE 802.11 (pronounced 802 dot 11) standard can be described as the father of
all WLAN standards. It evolved from a subcommittee within the IEEE 802 committee,
which is implied by the dot notation (the period) used in the standard number.

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This standard and its various revisions are the crux of most of our discussion in
this book. The IEEE 802.11 standards comprise various individual standards that cover
wireless networking technologies. These standards are forever evolving and adapting
to meet technology and industry needs. At the time of this writing, the most current
complete revision of this standard is IEEE 802.11-2007; however, several amendments
have been made to the standard after the 2007 major revision. Table 3-1 shows some of
the IEEE 802.11–based standards.
Note  It’s easy to take for granted the fact that the original IEEE 802.11 standard exists and was
actually a standalone standard that served an important purpose when it was first created. To be
pedantic, the IEEE 802.11 standard specified data rates of 1 megabit per second (Mbps) and
2 Mbps and operated in the 2.4 gigahertz (GHz) band. All the other IEEE 802.11 standards with
letter designations (such as 802.11b) are amendments to this original standard.
Amendments to the 802.11 standards are discussed next. And in continuing with
the genealogical analogy, some of these amendments can be viewed as the offspring of
the IEEE 802.11 standard.
IEEE 802.11b
The emergence of this standard represents the period when WLAN technology started
to be taken very seriously and gained mainstream adoption.
The IEEE 802.11b standard specifies a maximum raw data rate of 11 Mbit/s. In its
time, it was a dramatic improvement in the data rate compared with that offered by
the preceding IEEE 802.11 standard (11 Mbit/s vs. 2 Mbit/s). It uses the direct sequence
spread spectrum (DSSS)–based modulation scheme.
The standard specifies operation in the 2.4 GHz band, which makes WLAN devices
subject to interference from a plethora of other everyday devices that operate in the
same frequency range (such as microwave ovens and cordless phones).
Center
Bandwidth
Standard Frequency (MHz)
Data Rates (Mbps)
Modulation
802.11a 5 GHz 20
802.11b 2.4 GHz 20
6, 9, 12, 18, 24, 36, 48, 54
1, 2, 5.5, 11
OFDM
DSSS
802.11g 2.4 GHz 20
1, 2, 6, 9, 12, 18, 24, 36, 48, 54 OFDM and DSSS
802.11n 2.4 GHz 20
802.11n 5 GHz 40
7.2, 14.4, 21.7, 28.9, 43.3, 57.8, OFDM
65, 72.2
15, 30, 45, 60, 90, 120, 135, 150 OFDM
Table 3-1.  IEEE 802.11 Wireless Standards

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Chapter 3:  Wireless Standards
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Note  The maximum data rates specified by any of the 802.11 standards are achievable only in
a greenfield. A greenfield is an engineering jargon that describes an almost perfect environment.
For our application, greenfield refers to a wireless environment that lacks any constraints (such as
interference) imposed by existing wireless networks or other sources of interference.
IEEE 802.11a
The IEEE 802.11a standard specifies operation in the 5 GHz Unlicensed National
Information Infrastructure (UNII) frequency bands. It uses the same OFDM (orthogonal
frequency division multiplexing) modulation used in IEEE 802.11g (which is discussed
next). A maximum data rate of 54 Mbit/s is specified.
Because 802.11a does not operate in the crowded 2.4 GHz band, it is less prone to
interference. However, the higher frequency used results in a couple of disadvantages:
the overall range achievable is reduced, and the radio signals are more easily absorbed,
and therefore lost, due to the smaller wavelength of the 5 GHz radio waves.
Even though IEEE 802.11a–based devices can happily coexist with other wireless
devices that function in the 2.4 GHz industrial, scientific, and medical (ISM) bands, the two
devices cannot communicate with each other. They don’t operate in the same frequencies,
and the differences in the modulation techniques used by each also prevent them from
communicating. IEEE 802.11a devices use OFDM, while IEEE 802.11b devices use DSSS.
Devices that implement this standard are not as widely available in the marketplace
as devices that support the other standards.
IEEE 802.11g
The IEEE 802.11g standard specifies operation in the 2.4 GHz ISM band frequency.
The standard specifies a maximum raw data rate of 54 Mbit/s. It uses a variant of the
OFDM–based modulation scheme as well as the DSSS modulation technique.
Hardware based on the IEEE 802.11g standard is backward-compatible with IEEE
802.11b–based hardware. This backward-compatibility was a big plus that worked in
favor of the adoption of this standard, because users and system integrators were sure
that their investments in the early IEEE 802.11b hardware would not go to waste.
Because maintaining backward-compatibility with existing IEEE 802.11b devices
was a key principle guiding the design and specifications of the 802.11g standard, it
identifies three different modes of operation for the devices:
■■ g only mode  IEEE 802.11b clients are not invited to this party. Devices
operating in this mode use only the OFDM modulation scheme and are able
to support higher data throughputs than would be possible if they were
operating in any of the other modes.
■■ b only mode  Only wireless clients that are prepared to operate using DSSS
modulation scheme are invited. This is sort of a downgrade for 802.11g–capable
devices, because they are forced to use slower rates for communications. The
overall throughput in this mode of operation is roughly equal to that of the
slowest devices—in this case, the 802.11b devices—and, as such, data rates of
11 Mbit/s and less should be expected.

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■■ b and g mode  Everybody is invited to this party. This includes the devices
that support DSSS and/or OFDM modulation schemes, which include the
802.11b and 802.11g devices.
Even though it is an open party, some rules dictate the behavior of the attendees. This
rule is referred to as “protection mechanism.” It optimizes the performance of the
wireless network when both 802.11b and 802.11g clients are present.
Like other wireless hardware that functions in the crowded 2.4 GHz frequency
band, IEEE 802.11g devices suffer from interference from other devices that operate in
the same frequency band.
IEEE 802.11n
At the time of this writing, IEEE 802.11n is quickly gaining wide acceptance. Most
equipment manufacturers include several products in their portfolios that implement
the standard in one form or another. The standard specifies operation in the 2.4 and
5 GHz frequency bands. It can offer maximum data rates of up to 600 Mbit/s. It uses
the OFDM-based modulation scheme.
IEEE 802.11n offers overall improvements in comparison to the preceding standards.
One significant change that facilitates some of these improvements is its use of the
Multiple Input/Multiple Output (MIMO) technology. MIMO technology essentially
uses multiple antennas for transmitting and receiving, which lets it send and receive
more information than the standard dual- or single-antenna setups. Channel bonding,
which uses two non-overlapping and adjacent channels in the 5 GHz frequency band
for radio frequency (RF) communication, is also used in 802.11n. It is also known as
40 MHz, because it combines two channels, each with a width of 20 MHz.
The standard defines several built-in mechanisms that aid in the coexistence of
802.11n, 802.11b, 802.11g, and 802.11a wireless devices. One such mechanism allows
802.11n devices to embed their transmission inside 802.11g or 802.11a transmissions. This,
of course, makes the 802.11g and 802.11a devices happy, because it looks like everybody
is speaking the same language and can transmit at maximum possible speeds.
The vast improvements in throughput offered by 802.11n make it attractive for
use with applications such as streaming video, wireless Voice over IP (VoIP), video
conferencing, and others.
Note  For better or worse, we can thank the Wi-Fi Alliance for products in the marketplace that
implement standards that have not yet been fully ratified by the IEEE. Better because the Alliance
bypasses some of the red tape and bureaucracy in the standards-development process and helps
consumers get cool and new technologies more quickly. Worse because some of the standards
certified by the Alliance are not fully mature and are not ratified.
  Consider the Alliance’s certification of the IEEE 802.11n Draft 2.0 products long before the
standard became ratified by IEEE. Several vendors were able to make and sell products that
supported a standard that was still under development. I mention this only for historical reasons,
because IEEE 802.11n has, of course, since become a fully ratified standard.

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IEEE 802.11y
The IEEE 802.11y standard currently specifies operation of high-powered devices in the
3650 to 3700 MHz RF band in the United States. Its focus and primary application is not
for off-the-shelf and casual use. Devices implementing this standard can theoretically
link distances as far apart as 3 miles (5 kilometers).
Successful deployment of hardware implementing this standard is dependent on
minimal interference from other RF devices. And to this end, the standard specifies
several mechanisms that can help.
The first is the requirement of operators to obtain a so-called “lite license” before
being granted permission to operate base stations (also referred to as enabling stations)
implementing this standard. The license is nonexclusive.
The idea is that operators request and obtain a license from a regulatory body (such
as the U.S. Federal Communications Commission). The licensing requirements also
involve the base station operator specifying the physical location of high-powered base
station(s), which help in connecting the end user client devices that need to communicate
with or via the base stations.
The client devices do not need to pay for or request any special licenses to implement
this standard. To participate in an 802.11y network, the client devices require an “enabling
signal” from the licensed base station.
Another important concept is the Extended Channel Switch Announcement (ECSA),
which allows RF devices to dynamically change or select their current RF channel to a
channel that has the most favorable noise and quality characteristics.
IEEE 802.11k
This amendment to the IEEE 802.11 standard provides specifications on how to make
better use of available radio resources. It also details how better to manage the radio
resources by exposing radio and network information to facilitate easier maintenance
and management.
The IEEE 802.11k standard also aims to provide a standardization for new mechanisms
to supply the required measurements and metrics that will assist in more efficient radio
resource management.
It allows wireless clients to make more efficient and intelligent use of the radio
resources. For example, it can help a mobile client make a decision on the best access
point (AP) to connect to, by considering useful parameters (such as AP utilization)
other than signal strength.
IEEE 802.11i
IEEE 802.11i defines security mechanisms for wireless networks.
Unlike most of the other standards discussed thus far, IEEE 802.11i is not intended
to be used by itself as a wireless communication protocol. Instead, it is intended to
complement and or be layered on top of the other standards that deal with the actual
communications parameters.
The original IEEE 802.11 standard specified the use of 802.11 Wired Equivalent
Privacy (WEP) as a security mechanism. It was soon discovered, however, that several

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WEP weaknesses made it undesirable for use in protecting WLANs. And, true to form,
the IEEE 802.11 working group set up a task group to come up with a replacement
security solution, which is described in the IEEE 802.11i standard, more commonly
known as Wi-Fi Protected Access 2, or WPA2.
Note  When the brokenness in WEP was discovered, the Wi-Fi Alliance came up with a stop gap
security mechanism to replace WEP: Wi-Fi Protected Access (WPA). Weaknesses have since been
discovered in WPA, too.
IEEE 802.15
IEEE 802.15 refers to an IEEE 802 subcommittee that governs standards covering various
wireless personal area network (WPAN) technologies.
Several task groups exist within the IEEE 802.15 subcommittee and were formed to
focus on different WPAN implementations:
■■ Task Group 1  This group developed standards that were based on some of
the early specifications developed by the Bluetooth special interest group. IEEE
standards exists for Bluetooth versions 1.1 and 1.2.
This task group was short-lived and came up with only a couple of IEEE
standards before disbanding.
■■ Task Group 2  This task group deals with issues concerning the coexistence of
devices that implement WPAN standards and those that implement the WLAN
standards.
■■ Task Group 3  This group developed standards for the “High Rate WPAN”
technologies.
■■ Task Group 4 (IEEE 802.15.4)  This task group developed standards for the
“Low Rate WPAN” technologies. The standard is well suited for wireless
applications that require low data rates and minimal power consumption. The
IEEE 802.15 standard is at the heart of various commercial implementations,
such as the popular ZigBee. The ZigBee Alliance is a group of companies that
maintain and publish the ZigBee specifications. The functions of the ZigBee
Alliance are similar to those of the Wi-Fi Alliance in the WLAN world.
Summary
Even though it wasn’t mentioned explicitly, standards help drive the multi-billion-dollar
wireless industry. You should now understand the benefits and importance of standards,
and you should appreciate the relationship between the regulatory organizations,
technical organizations, and standards formulating bodies. You saw firsthand the results
of the hard work put in by the technical organizations discussed in Chapter 1.
You also learned about some legacy, current, and future standards that directly affect
the end products and quality of the products that we as wireless network administrators
need to manage.

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Part II Hardware

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Key Skills and Concepts
■■ Identify what constitutes client-side hardware.
■■ Understand the role and importance of the chipset in wireless hardware.
■■ Learn about some popular chipset manufacturers in the wireless industry.
■■ Learn about the different interface types for wireless client hardware.
Concepts, theories, and standards are all important, but what good are they if
we can’t actually put them to work? In this part of this book, we’ll look at some
of the hardware that implements the concepts, theories, and standards that
were covered in the chapters in Part I. This chapter and the next look at three broad
categories of hardware: chipsets (which are found in client-side and infrastructure-side
hardware), traditional client-side hardware, and infrastructure-side hardware.
Strictly speaking, this chapter discusses client-side components and their features.
Our so-called “client-side hardware” includes things you might find in complete and
finished products, such as wireless client stations, which are combined with other
pieces to form a whole. In this book, a “client-side device” refers to any hardware that
participates in a wireless network and meets any two of the following descriptions:
■■ Client-side devices are generally self-sufficient and are useful by themselves.
This means that they can serve purposes other than wireless networking–
related functions.
■■ The device is naturally selfish—it does not normally provide any type of
service to other devices. It is concerned only with itself.
■■ The device might easily fit into a tote bag or a shirt pocket.
You will also see mentioned some hardware that is not strictly client-side or strictly
infrastructure-side.
We begin this chapter by delving into the world of chipsets.
Chipset
In the information technology (IT) world, the chipset is a somewhat abstract concept—
it is always there, but it can be difficult to pinpoint or define exactly. Even though we
refer to a chipset as though it were one single hardware component, it is in fact a group
of specialized integrated circuits (ICs) that are designed to work together in symphony
to perform specific tasks. To confuse issues even more, a chipset can have different
meanings, depending on the industry that uses the term—be they graphics, audio, or
network communications industries.

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In this book, chipsets used in the wireless network communications industries
are the focus. These chipsets are used primarily for analyzing, interpreting, and
manipulating radio signals—also known as signal processing. Specifically, we are
interested in chipsets that implement the IEEE 802.11 and other wireless standards in
one form or another.
Components of a Wireless Chipset
A chipset comprises several discrete components that work in unison to give the
illusion of singleness. But that mythical illusion will be dispelled here.
Most chipsets used in wireless communication systems comprise separate integrated
circuits that are responsible for handling Media Access Control and Baseband Processor
(MAC/BBP) functions and the Pure Radio functions of a wireless communications
system. On the whim of the chipset manufacturer, other miscellaneous functions may
also be embedded into the circuits, such as hardware-based encryption.
Media Access Controller and Baseband Processor
The MAC hardware component controls and negotiates access to the transmission
medium for the radio waves. The transmission medium in this case is the air or
free space. “Baseband” is a term used in electronics to refer to the original and
unadulterated group of signals (bits) originating from a data source before any kind
of modulation takes place on the signal. The BBP hardware takes care of converting
these baseband signals from digital to analog form (known as modulation) and then
back again (known as demodulation) at the other end of the communication channel.
Basically, the BBP is where modulation and demodulation take place.
The MAC/BBP component of a wireless communication chipset jointly performs
the following functions:
■■ Interfacing with the host system via the applicable bus or interface type—such
as via Peripheral Component Interconnect (PCI), CardBus, Mini PCI, or
Universal Serial Bus (USB)
■■ Handles the analog-to-digital conversion (ADC)
■■ Handles the digital-to-analog conversions (DAC)
■■ Handles power management functions for the chipset
■■ Processes media access techniques, such as Carrier Sense Multiple Access with
Collision Avoidance (CSMA/CA)
■■ Implements the modulation technique and the physical layer (PHY) properties of
the IEEE 802.11 or other standard; for example, direct-sequence spread spectrum
(DSSS, used in IEEE 802.11b), orthogonal frequency division multiplexing
(OFDM, used in IEEE 802.11a/b/g), quadrature phase shift keying (QPSK), and
differential phase shift keying (DBPSK)

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Wireless Network Administration: A Beginner’s Guide
Radio Frequency Transceiver
The integrated circuits in the radio frequency (RF) transceiver component of a wireless
chipset handle the following functions:
■■ Reception of RF signals
■■ Transmission of RF signals
■■ Power amplification and low-noise amplification
■■ When applicable, provides an interface to the antenna
Figure 4-1 depicts the position of a wireless chipset in a wireless communication
system.
Chipset Makers
The chipset industry is dominated by a few manufacturers (a vertical market), and
every device manufacturer that requires the functionality provided by a chipset obtains
it from one of these manufacturers. This is why so many different hardware brands
from different manufacturers carry the same chipset, and it’s why some wireless
hardware drivers can be used across different hardware brands.
These device manufacturers add on a few extra customizations, stuff it all in nice
cases, slap on their company logos, shrink wrap the products, include their markup,
generate a lot of marketing material and thick manuals for the products, and then put
them on the store shelves (horizontal market).
Air
Analog signal
RF
transceiver
Media Access
Controller
Baseband
processor
Misc. circuits
(e.g., encryption)
Antenna
Chipset
components
Figure 4-1.  Chipset in a wireless communication system
Chipset
101000101...
(digital)
Wireless device

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43
Chipset Manufacturer Chipset Code
Wireless Equipment Manufacturer
Atheros
Communications
Broadcom
Cisco Systems
Texas Instruments
Alcatel-Lucent
Intel
Realtek
Semiconductor
Ralink Technology
AR9002, AR9001, AR5008, Netgear, D-Link, and TRENDnet
AR5007, AR5006, AR5005,
AR5002
Bcm43xx, BCM47xx
Apple, Belkin, Dell
Aironet
Cisco
acx111, acx100,
acx100_usb
D-Link, US Robotics, Airlink,
Netgear, Linksys
Orinoco, Hermes
3Com, Apple, D-Link, Intel,
Microsoft, Toshiba, Farallon,
Avaya
Intel PRO/Wireless (IPW) Dell, Intel
2200BG/2915ABG/
3945ABG/4965AGN
RTL818x, RTL8187B
Netgear, Belkin, D-Link,
Linksys, Zonet
RT2500, RT2501, RT2600,
RT2501USB, RT2800,
rt2x00
Gigabyte Technology, Linksys,
D-Link, Belkin, Nintendo
Table 4-1.  Sample Chipset Manufacturers
Some chipset manufacturers and companies that use the chipsets in their products
are shown in Table 4-1. Note that the information in the table was current at the time of
this writing.
Note  Some chipset implementations work in conjunction with firmware, and the functionality of
the chipset is closely tied to the firmware. The firmware contains the main program to be run by a
wireless card’s chipset. This will be discussed in more detail later in the book.
Client-Side Wireless Hardware
Any piece of client-side wireless hardware always has at least one chipset embedded
in it to perform various functions. Almost anything conceivable can be turned into a
wireless client these days—from the humble toaster, to big and powerful computers.
The toaster example may seem a bit far-fetched, but, truth is, as long as we can find a
way to slap a radio on it, we can turn it into a node in a wireless network. It’s all about
the interface and how we intend to communicate with or over that interface.

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Wireless Network Administration: A Beginner’s Guide
A client-side device needs to participate in a wireless network. In wireless local area
network (WLAN) lingo, such a device is often referred to as a WLAN station (STA).
Some client-side WLAN hardware may appear to be built into the host system, but
you should understand that even when this is the case, the devices will still need to
communicate with other hardware, using one or a combination of interface technologies.
Now let’s look at some common wireless client hardware interfaces, their incarnations,
their form factors, and their bus interconnect types. These devices either provide
an interface to the wireless chipset on the host system or have the wireless chipset
embedded in them already.
PCI
Peripheral Component Interconnect (PCI) is a communication bus architecture over which
PCI-based devices can communicate. Specifications that govern PCI are developed and
defined by the PCI-SIG (PCI Special Interest Group), an international consortium.
Devices using the PCI architecture communicate by sending data signals
simultaneously over parallel channels. Wireless hardware implementations using this
interface often come in the form of wireless PCI expansion cards. They offer a cheap
and easy way to allow most standard consumer PCs or servers to participate in a
wireless network. Almost all modern computers still support this interface standard.
Wireless cards that use this interface often offer the added benefit of being able to
use detachable antennas. This capability provides a cheap and easy way of boosting the
reception capabilities of a WLAN device. Figure 4-2 shows a sample PCI wireless card.
Figure 4-2.  PCI wireless card

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Mini PCI
Mini PCI is a PC expansion interface standard. It is small form factor implementation
of the PCI standard and is found primarily in laptops and other portable computers.
Devices that use this interface communicate with the host over the PCI bus.
The Mini PCI standard is based on a subset of the same signal protocol and
electrical characteristics as the main PCI specification. Hardware implementations
of this standard are therefore functionally identical to full-sized PCI cards that are
used in desktop systems.
Numerous hardware applications built around the Mini PCI standard are used for
providing Bluetooth, WLAN, Ethernet, and modem support on host devices. Figure 4-3
shows a sample Mini PCI card.
Older laptops usually sport wireless cards that use this interface technology. Mini
PCI cards have been superseded by PCI Express Mini cards, discussed next.
PCI Express Mini
PCI Express Mini (also known as Mini PCIe) is the PC expansion interface standard
and an incarnation of the PCI Express standard. Specifically, it is a small form factor
implementation measuring 30×56 mm, making them smaller than Mini PCI cards.
Devices that use this interface communicate with the host either via PCI Express bus
or via USB 2.0. The communication is via point-to-point serial links.
Wireless cards found in newer laptops are usually of the Mini PCIe type and
connect via a Mini PCIe expansion interface on the host. Figure 4-4 shows a sample
Mini PCIe card.
Figure 4-3.  Mini PCI card

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Wireless Network Administration: A Beginner’s Guide
Figure 4-4.  Mini PCIe card
PC Card
The PC Card standard was developed by a group of companies originally known as
the Personal Computer Memory Card International Association (PCMCIA). The group
initially envisaged its standard to be an alternative to an existing standard developed
by another group called the Japan Electronic Industry Development Association
(JEIDA). The two groups later had a change of heart and decided to streamline the two
competing standards.
Peripherals using this standard are designed especially with laptops in mind and
also to fit into small spaces—Ethernet cards, WLAN network cards, modems, and
so on.
The PC Card standard has gone through several (confusing) hardware generations
based on several (more confusing) revisions. All generations of the hardware use a
68-pin connector and are all the same length (85.6 mm) and width (54 mm) but have
varying thicknesses. Some PC Card standards and their associated form factors are
listed in Table 4-2.

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Standard
Supported Form
Factor(s)
Features
PCMCIA version 1 Type I, Type II
PCMCIA version 2.0 Type II
JEIDA version 4.1
PCMCIA version
2.01
Type III
PC Card version 5.0 CardBus
Type I:
■ Implemented in older hardware
■ Supports only a 16-bit interface
■ Uses the hosts’ ISA parallel bus
■ Designed mostly for memory card type
applications and not input/output type
applications, such as networking
■ Supports throughputs of up to 20 MBps
■ Cards are 3.3mm thick
■ Merges competing PCMCIA and JEIDA
standards
■ Support for input/output type
applications
■ Support for dual voltage cards: 3.3 and
5 volts
■ Often must be used with dongles
because the cards are usually no more
than 5.5 mm thick
■ Supports throughputs of up to
7.84 MBps
■ The PCMCIA body started adopting the
“PC Card” moniker
■ Come in 16- or 32-bit interfaces
■ Physically almost double the thickness
(10.5 mm) of preceding Type II cards
■ Adds support for the 32-bit CardBus
interface
■ Operates at 3.3 volts
■ Supports throughputs of up to
132 MBps
■ Cards are easily identifiable by metal
strip on top of their sockets
■ Slots are backward-compatible with
preceding slot/interface types
(Type I, II, III)
Table 4-2.  PC Card Standards

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Wireless Network Administration: A Beginner’s Guide
ExpressCard
ExpressCard is the next generation hardware standard developed to replace devices
based on the PC Card technology. ExpressCard is based on a standard developed by
the PCMCIA standards body.
ExpressCard hardware can interface with the host system via a serial interface, either
over a USB 2.0 interface or a faster PCI express bus. Devices based on this technology
support higher data bandwidth compared with the PC Card technology. Throughputs
of up to 2.5 Gbit/s (gigabits per second) are supported in this standard when the PCI
Express bus is used, and throughputs of up to 480 Mbit/s are supported when using the
slower USB 2.0 interface. Devices using the interface sport a 26-pin connector.
ExpressCard offers several advantages over CardBus:
■■ Smaller form factor
■■ Doubles the data rates supported in CardBus
■■ Less power drawn from the host for more efficient power use
■■ Costs less to make and implement, due to elimination of an intermediary
controller required in CardBus
A good comparison of newer ExpressCard and older CardBus technologies is shown
in Figure 4-5.
ExpressCard 54
Two widths (34 mm and 54 mm)
ExpressCard 34
75 mm
85.6 mm
CardBus PC Card
Universal
slot
Guidance
feature
34 mm
slot
CardBus
slot
Figure 4-5.  ExpressCard technology vs. CardBus
3.3 V, 1.5 V, 3.3 Vaux
PCI Express
USB 2.0
26 pin connector
System
chipset
PCI Express
USB 2.0
Native
bus
attach
68 pin connector
CardBus
CardBus Legacy
controller bridge
5.0 V, 3.3 V, 3.3 Vaux

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75 mm
ExpressCard 34
26 pin
connector
Figure 4-6.  ExpressCard 34
Peripheral cards that are built for the ExpressCard interface come in two form
factors. The first form factor is rectangular in shape and is referred to as ExpressCard
34. This form measures 75×34mm (Figure 4-6).
The second form factor is L-shaped and is referred to as ExpressCard 54. It measures
75 mm at its longest length and 54mm at the widest width (Figure 4-7).
Most newer laptop models support ExpressCard interfaces. This standard is used in
making PC peripherals for wireless WAN, IEEE 802.11 WLAN, and other applications
that can benefit from the high data rates supported.
USB
Wireless USB devices are a popular method for adding WLAN capabilities to a host
device. They are often in the form of a dongle (an electronic device that is usually attached
to a computer externally) that can simply plug into any available USB port on the host
system. Wireless cards designed to be plugged into the USB port of the host device often
do not have any interface in which to plug an external antenna, as the antenna is often
built into the device itself. A typical wireless USB adapter is shown in Figure 4-8.
You’ll find plenty of wireless USB devices that implement virtually any of the
individual IEEE 802.11 family of standards. Read the supported standards and platforms
on the packaging box, and you should be good to go.
75 mm
54 mm
ExpressCard 54
34 mm
Figure 4-7.  ExpressCard 54

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Wireless Network Administration: A Beginner’s Guide
Figure 4-8.  Typical wireless USB adapter
WLAN devices that connect to a host via an external USB port are especially
convenient for several reasons:
■■ Installing the hardware is easy and does not usually involve cracking the
computer case open.
■■ They are not dependent on having an empty PCI, PCIe, or PCMCIA slot
available.
■■ An abundance of USB ports are available on most host systems.
■■ The host system does not need to have any preexisting built-in wireless
chipsets to become a wireless STA.
■■ They make it easy to enable most old or newer computer hosts to participate in
a WLAN network.
Note  In addition to their WLAN hardware applications, wireless cards using the USB interface
are popular in devices for connecting to high-speed mobile broadband networks.
CompactFlash Cards and SDIO Cards
Portable devices such as personal digital organizers (PDAs), digital cameras, portable
media players, mobile phones, and GPS receivers have now become an ubiquitous part
of our lives and by extension part of the WLAN administrator’s nightmare. You can
add wireless capabilities to a lot of these devices cheaply and with little effort.
Portable device manufactures have lowered the costs of their devices by making Wi-Fi
capabilities in their devices optional for the end user. The user can choose whether or not

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51
802.11
Wireless
SDIO
card
Wireless
CompactFlash
card
Figure 4-9.  SDIO and CF cards
they require wireless functionality on the device. If the user requires this functionality,
his or her choices to achieve this are limited only by the interface types and technology
supported by the device vendor. In most cases, choices range from using the CompactFlash
(CF) interface or a Secure Digital (SD) card interface on the host device.
In the wireless LAN (WLAN) world, CF cards are used for adding wireless capabilities
to portable handheld devices (such as PDAs) that don’t have this capability. CF cards are
especially useful in this role because they require and draw very little power from their
hosts, where battery conservation is already an issue.
Secure Digital Input Out (SDIO) is a memory card format, an extension of which
can be used for various applications that include Bluetooth, Wi-Fi, and radio-frequency
identification (RFID), to mention a few. SDIO cards connect to the host via the host’s SD
card. The SD card slot on support devices is normally used for extending the storage
capabilities of the host, but certain devices are capable of using their SD card interface
for communicating with SDIO cards. Figure 4-9 shows SDIO and CF cards.
Miscellaneous Converters
Popular in this category are Ethernet-to-wireless converters and serial-to-wireless
converters that are used for providing wireless capabilities to dumb legacy devices,
such as serial printers that have no wireless capabilities and no easy way to provide
such capabilities using a software (driver) and hardware combination. These interface
converters are usually stand-alone devices and do not often offer the wireless network
administrator any graphical user interface (GUI) with which to configure them.
Configuration of these devices is usually done via a serial port on the devices.
Other Considerations for Choosing Wireless Hardware
When making decision about which wireless client devices to use for a WLAN, you
should consider several factors. One of these considerations is the already discussed
obvious choice of the form factor and interface of client device (obvious, for example,
because it is physically impossible to fit a Wireless PCI card into a the USB slot of a
laptop). Other considerations for selecting wireless client devices are discussed next.
Note that these considerations are also applicable to wireless infrastructure hardware.

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Wireless Network Administration: A Beginner’s Guide
Transmit Power (Tx Power)
Communication, as we all know, is a two-way street. We have the talking lane and
the listening lane (let’s ignore the existence of one way streets for now). In the WLAN
world, this is akin to the transmitting and receiving of data that has been encoded as
radio signals.
Transmit (Tx) power is relevant on the talking lane of our two-way street. It is the
amount of radio frequency power that a transmitter produces at its output. Transmit
power values are often expressed in milliwatts, but they can also be expressed as watts
or decibel milliwatts (dBm). The transmit power of WLAN equipment is generally less
than 1000 milliwatts (1 watt), and values are often represented as positive numbers.
The transmit power has a direct relationship with the range of an RF signal. In other
words, the higher the transmit power, the further the signal can travel to its intended
(and unintended) destination. As discussed in Chapter 2, the property of a radio wave
that affects its power is its amplitude.
Receiver Sensitivity (Rx)
This characteristic is relevant on the listening lane of our two-way street—the receiving
end of the communication. The receiver sensitivity is a somewhat tricky measure, and
few device manufactures bother to supply hard figures for this characteristic. It is a
measure of the minimum threshold at which a WLAN client device can properly detect
and interpret a radio signal.
The unit of measurement for the receive sensitivity of a wireless device is the dBm.
The measurement values are often expressed as negative numbers, so a wireless device
with a low receiver sensitivity value (such as –90 dBm ) can receive and better interpret
radio signals than another device with a higher receiver sensitivity value (such as
–70 dBm). In other words, the lower the receiver sensitivity, the weaker the signal the
wireless device can pick up—which is a good thing.
Summary
The chipset is integral in the grand scheme of almost all wireless communications
hardware. Some big players in the chipset world use various hardware interfaces and
form factors to create these chipsets in all shapes and forms.
Client-side wireless hardware comes in different types and with different interfaces.
The interface used depends on the available interface on the host device and also on
how we intend to communicate over that interface.
Amongst other things, a wireless network administrator must consider two important
RF measures when selecting wireless client hardware: the transmit power and the receiver
sensitivity.
The next chapter discusses some of the hardware used on the infrastructure side of
wireless networks.

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Wireless Hardware:
Infrastructure Side
53

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Wireless Network Administration: A Beginner’s Guide
Key Skills and Concepts
■■ Understand what constitutes infrastructure-side wireless hardware.
■■ Understand the function of an antenna in wireless communications.
■■ Learn the various concepts associated with antennas.
■■ Identify different antenna types.
■■ Understand the functions of wireless access points and residential gateways.
■■ Understand the functions of wireless controllers and wireless bridges.
■■ Learn the basics of Power over Ethernet.
Chapter 4 discussed the wireless hardware found on devices that serve as clients
on a wireless network. This chapter covers the hardware that makes up the
infrastructure end of things. These hardware can individually and collectively
connect end nodes (clients) on a wireless network. Some of the hardware and hardware
interfaces used in wireless clients are also present in infrastructure devices. For example,
the same types of chipsets used in client hardware are often used in the infrastructure
devices as well.
Broadly speaking, what this book calls an “infrastructure-side device” is any hardware
that participates in a wireless network that meets any two of the following criteria:
■■ Helps to connect other wireless devices together
■■ Provides a service to a wireless client
■■ Will not easily fit into a tote bag
As you will discover later, some devices fall into a “gray area” regarding these
criteria—but read on and you’ll understand why this is so.
Antenna (Aerial)
In Chapter 4, you read that antennas (also called aerials) are usually built into wireless
radio cards used on the client side. But those types of antennas are small and nice-
looking. In this chapter, when antennas are mentioned, think big. Think massive. Think
antennas that need to be positioned 300 feet above sea level. Antennas that are 500 feet
in diameter. Think satellite dishes. Seriously speaking, antennas come in all shapes and
sizes. A manufacturer designs its antennas to suit specific applications. If the antenna is

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meant to fit into a small ExpressCard form factor, it has to be very small. On the other
hand, if it is meant to link two remote buildings together, it will be very large (and will
most likely not fit into a tote bag).
An antenna is the first port of entry and exit for the radio signals passing through
a wireless communications system. It is the hardware from which the radio waves
emanate and to which radio waves aggregate.
The electronics in any wireless hardware send electrical signals to the antenna, and
the antenna converts this electrical current into electromagnetic waves, which then
propagate through the air to the final destination. This destination is usually another
antenna, which may be embedded in a wireless client hardware or some other wireless
infrastructure device. After they arrive at their destination, the electromagnetic waves
are converted back into electrical signals.
Antenna Concepts
Several common terms and concepts are important to know regarding antenna
characteristics. These concepts and terms will help you understand discussions on
antenna types.
Intentional Radiator
The intentional radiator (IR) is any hardware component of a wireless communications
system that intentionally generates and emits radio frequency (RF) energy. By definition,
the IR is distinct from the antenna. The IR consists of components such as the transmitter,
amplifiers, cables, and other knobs and dials found in wireless devices. The IR ends
where the antenna starts. Cordless phones, walkie-talkies, and wireless cards are all
good examples of IRs (excluding the antenna portion, of course).
An IR is in contrast to an unintentional radiator, which does not deliberately generate
RF energy but does generate it as a by-product. Examples of unintentional radiators are
electrical transformers and dynamos.
Regulatory bodies within each country govern the maximum RF power levels that
an IR can produce. One of the reasons this is necessary is for safety—that is, we don’t
want humans exposed to too much RF energy. This is because the exact long-term
effects of RF energy on human health is unclear. In addition, RF-generating devices
can sometimes interfere with the proper functioning of other electronic devices, like
lifesaving equipment, such as pacemakers.
Equivalent Isotropically Radiated Power
Equivalent isotropically radiated power (EIRP) is a measure of the amount of actual
power emitted from an antenna. The EIRP acronym sometimes represents effective

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Wireless Network Administration: A Beginner’s Guide
isotropically radiated power. The isotropy in EIRP describes an ideal situation whereby
the radio energy is assumed to be equally distributed in all directions. This type of
ideal situation, of course, does not exist in the real world.
EIRP is a measurable quantity. It is the sum total of the power output from the IR
and the passive gain (or loss) caused by the antenna. Regulatory bodies within each
country also govern the values of the EIRP of wireless devices.
The following illustration shows the IR and EIRP components of a simple wireless
station (STA).
EIRP area
IR area
Wireless STA
Antenna Gain and Loss
An antenna can cause either a gain or a loss in the RF signal it is transmitting or
receiving. The type of gain or loss caused by an antenna is passive in nature, in the
sense that the antenna does not actively cause gain or loss in RF signal strength by
using any special electronics (such as amplifiers or attenuators). Instead, an antenna
can cause signal gain because it helps to focus or concentrate the RF signal in a specific
direction. And, conversely, an antenna can result in reduction in the effective signal
strength by simply unfocusing it.
The following illustration depicts the before and after effects of introducing a
high-gain antenna into the communication channel between wireless STAs—WAP 1

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57
and WAP 2. It shows how an antenna can produce gain in the RF power by making the
signal more focused.
Before Antenna
25% wasted RF signal missing WAP 2
WAP 1
50% useful RF signal reaching WAP 2
WAP 2
25% wasted RF signal missing WAP 2
After Using a Passive Gain Antenna at WAP 1
2% wasted RF signal missing WAP 2
96% useful RF signal reaching WAP 2
WAP 2
WAP 1
2% wasted RF signal missing WAP 2
Beam Width
Beam width is a measure of the horizontal and vertical reach of the RF signals
transmitted from an antenna. Beam width is measured in degrees. The vertical
beam width is perpendicular to the ground, and the horizontal beam width is
parallel to the ground.
The beam width specification of an antenna is important in choosing an antenna
that will provide the coverage needed for a specific area. Practically speaking, this
could mean that in some situations, an antenna with a narrow beam width is more
desirable than an antenna with a wide beam width.
Polarization
An electromagnetic wave comprises two components: an electric component and
a magnetic component.

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Wireless Network Administration: A Beginner’s Guide
The electric component is also called the E-plane. The E-plane is parallel to the
conductor, or element, of the antenna. The magnetic component is called the H-plane.
The components are perpendicular to each other. Electromagnetic waves travel in a
direction that is perpendicular to both the electric and magnetic components.
Polarization of an antenna is affected by the physical orientation of the antenna.
When the antenna is oriented vertically, the polarization is vertical, which also
means that the E-plane is perpendicular to the ground. This is the case, for example, with
the types of antennas that are normally oriented vertically, such as in omnidirectional
antenna (more on this later in this chapter). The following illustration shows a vertically
oriented antenna with the equivalent E-plane and H-plane:
E-Plane
H-Plane
When the antenna is oriented horizontally, the polarization is horizontal, which
means that the E-plane is parallel to the ground. This is the case, for example, with
the types of antennas that are normally oriented horizontally, such as yagi antennas
(more on these a bit later). The following illustration shows a horizontally oriented
antenna with the equivalent E-plane and H-plane:
H-Plane
E-Plane
In a wireless communications system, the transmitting and receiving antennas
should be polarized in the same direction to achieve best results.

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Antenna Types
The shape and properties of an antenna are determined by the application and
environment in which it will be used. Antenna types are categorized as omnidirectional,
semidirectional, and directional.
Omnidirectional Antennas
Omni means all. Omnidirectional antennas transmit signals in all directions and
receive signals from all directions. Omnidirectional antennas transmit and receive RF
signals in 360 degrees. The horizontal beam width of the RF signal emanating from an
omnidirectional antenna is 360 degrees, and the vertical beam width is usually between
7 and 80 degrees.
These are probably the simplest, cheapest, and most common types of antenna
available. They are frequently found in commodity wireless hardware used on the
client and infrastructure sides. A dipole antenna is an example of an omnidirectional
antenna.
The wave pattern of the radio waves transmitted and received from omnidirectional
antennas is said to be shaped like a toroid, or a ring donut, as shown in the following
illustration:
Omnidirectional antennas are best suited for use in environments such as the center of
a room or space because of the 360-degree horizontal coverage they offer. The signal
emanating from omnidirectional antennas propagates more horizontally than vertically.
Whenever coverage is needed in relatively equal amounts all around a horizontal
space, an omnidirectional antenna should be considered. Just remember that they are
not suited for environments in which vertical coverage is more desirable, such as the
lower and upper floors of a building. Omnidirectional antennas are often used for
indoor applications for which radio signals are transmitted from one device to multiple
devices at the same time—called point-to-multipoint or one-to-many systems.

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Numerous stand-alone omnidirectional antennas are designed to be attached and
used with wireless client devices such as PCMCIA cards, PC Cards, and PCI Cards.
Semidirectional Antennas
Semidirectional antennas radiate and receive RF signals in a roughly 180-degree beam
width. Several types of semidirectional antennas are available. When used indoors,
semidirectional antennas can be placed on a wall facing the desired direction or
mounted on the ceiling facing down.
In terms of application, outdoor semidirectional antennas are best suited for short-
to-medium haul transmissions and receptions.
In terms of placement, these antennas are best placed in locations where signal
reception is needed in one direction and not so much in the other, such as at the end of
a long hallway with offices on either side.
The wave pattern of the radio waves transmitted and received from semidirectional
antennas is shaped like a ring donut cut in half.
Planar Antennas  Planar antennas are a special subcategory of semidirectional antennas.
They do not have the conventional antenna physical structure. Because of their internal
design and the flexibility offered as a result, planar antennas can come in various
shapes and sizes. They are usually deployed for indoor applications and are not often
easy to spot because they can be packaged so that they blend in with the rest of their
environment.
As diminutive and harmless as they appear, planar antennas are used for very
serious applications, such as cellular, broadband, WLAN deployments.
Yagi  A yagi antenna is commonly used for outdoor applications. They also come in
several shapes and sizes, but a distinctive physical feature is that they usually have
some kind of protruding snout that emits the RF signals. As with most other types of
antennas, a yagi antenna’s signal gain comes from its ability to limit the horizontal and
vertical beam width of the RF signal.
Figure 5-1 shows a sample yagi antenna.
Figure 5-1.  Yagi antenna

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Directional Antennas
Directional antennas focus their radio waves in a very specific single direction. The
horizontal beam width of the RF signal emanating from a directional antenna is between
4 and 25 degrees, and the vertical beam width is usually between 4 and 21 degrees. These
antennas generally provide high signal gain, and installation and handling should be
undertaken with great care to avoid undue exposure to high-power RF radiation.
The wave pattern of the radio waves transmitted and received from directional
antennas is shaped almost like a cone.
These antennas are best placed in locations with a clear line of sight to the receiving
end of the communications system. Most often, the receiving end will also be another
directional antenna. This makes these types of antennas suitable for point-to-point
applications. Directional antennas are best suited for medium-long haul transmissions
and receptions.
Note  It might seem like these antennas do a perfect job of focusing their radio waves in the
direction for which they are designed, but this isn’t specifically true. All antennas propagate some
RF energy in some unintended directions, even though an important antenna design objective is to
limit this unintended transmission as much as possible.
Other Antenna Considerations
The placement and type of antenna used can be the defining factors of good signal
transmission and reception for wireless communications. Even though most wireless
devices ship with their own antennas, a wireless network administrator sometimes
needs to swap out the original antenna and replace it with one that works better for
a specific situation. In addition, numerous wireless device manufacturers’ products
allow the end user to choose the most suitable antenna for specific applications.
It may be necessary for the wireless network administrator to consider wireless
antennas in the following situations:
■■ The default antenna is not adequate for transmitting the desired signals to the
destination.
■■ The default antenna is unable to receive the desired signals.
■■ The antenna is causing the wireless device to violate local wireless regulatory
rules.
■■ The wireless device does not ship with an antenna, but includes a connector for
attaching an appropriate antenna.
Antenna Checklist
If the wireless network administrator determines that an antenna is needed for a
specific application or scenario, it is important to select the best antenna for the job.

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Several factors should be taken into consideration in antenna selection. These
would include polarization, beam-width, antenna gain, antenna loss, as well as the
following additional considerations:
Outdoor vs. Indoor Antenna  Antennas that are designed for mounting outdoors are
different from indoor antennas. The differences are not necessarily in the electronics or
functionality of the antenna but are often in the shape, protective enclosure, and other
physical characteristics of the antennas that are designed for outdoor use. In general,
you would want an outdoor antenna to be weatherproof so that the electronics are
well-protected come rain, snow, or sunshine.
Aesthetics  When it comes to antennas, looks can matter. The enclosures of some
antennas are designed so that they blend well with the interior or furniture in a space.
Some antennas are designed to be as inconspicuous as possible.
Mounting Kits  This is an important consideration when selecting an antenna. If an antenna
needs to be mounted on an external surface, you must carefully choose the parts used for
the mount. Most antenna manufacturers supply mounting brackets and kits that work
with their hardware. But the manufacturer’s mounting kit might not be suitable for your
application; in this case, you’ll need some third-party solutions for the mounting pieces.
For example, the mounting parts needed for mounting an antenna on a wall will be
different from those needed for mounting an antenna on a pole or a ceiling.
Placement  The actual placement of the antenna is another important consideration.
Indoor antennas need to be placed in a location that will receive minimum interference
from other electrical devices; immovable objects, such as walls, ceilings, or signs; or
even humans. Sometimes, unavoidable environmental factors can affect the radio
communications for which the antenna is being used.
Outdoor antenna placement can also be critical. Local regulatory laws regarding
outdoor structures may also apply, and these laws can influence the total height, size,
and appearance of an outdoor antenna. Make sure that you are not breaking any local
laws with the antenna.
Don’t forget that the antenna also needs to be easily reached should it require service
or repair. Place the antenna so that it is easily accessible.
Safety  Proper grounding procedures should be followed when installing outdoor
antennas, which are exposed to lighting and other natural phenomena and are directly
connected to indoor electrical devices. Indoor antennas should be placed where they
pose no dangers to humans, including physical or overexposure dangers, or where they
could interfere with radio signals used on lifesaving equipment, such as equipment
used in hospitals.
Wireless Access Point
A wireless access point (WAP) provides a means for wireless nodes (also known as
Wireless Stations) to communicate with other wireless nodes or to communicate with

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a wired network. A WAP is often simply referred to as an access point (AP). They are
commonly used in enterprise-type environments where the functions of networking
hardware must be properly segmented—that is, these devices do not typically perform
all functions but are instead designed to perform specific functions very well.
Traditional WAPs are somewhat distinct from wireless residential gateways or
wireless routers because they do not normally perform Open System Interconnection
(OSI) Layer 3 type routing functions. They instead rely on other components on the
network to perform such functions.
The line between the role of WAPs and wireless gateways is getting more and more
blurred with time as wireless network equipment manufacturers are consolidating all
these functions into single-purpose solutions. There are advantages and disadvantages
to this. One disadvantage is that the single AP acts as a single point of failure in the
network. This means that if any of the components or functions fail, the device could
bring down the entire network. On the other hand, having major functions of the
wireless network available in one multipurpose device can make the wireless network
administrator’s job a lot easier.
You can identify traditional WAP hardware by its lack of a distinct wide area network
(WAN) interface. Instead, it usually has only local area network (LAN) interfaces with
which it connects to the LAN segment.
In addition to connecting wireless clients to a wired network, WAPs can also feature a
combination of the following: security functions, MAC layer filtering functions, protocol
layer filtering, VLAN functionality, detachable antennas, field replaceable radio cards,
and Power over Ethernet, to mention a few. Some of these functions are covered in more
detail later in the book.
WAP Operational Nodes
Wireless APs use three operational modes: root mode, the most fundamental and
natural mode in which a WAP operates; bridge mode, used for bridging two or more
networks together; and repeater mode, which helps to extend the reach of a wireless
network. Figure 5-2 shows the three operational modes of APs.
Root Mode
In this mode, also called infrastructure mode, a WAP is performing its basic function—
connecting wireless clients to a wired network. Root mode is also used for intermessaging
or management purposes when APs need to communicate among themselves (for
example, when two or more APs are combined for STA roaming purposes).
Bridge Mode
WAPs operating in bridge mode can be used to connect two or more wired networks
together. The bridged network normally ends up being on the same subnet and shares
a common broadcast domain. When operating in this mode, wireless clients are usually
unable to connect wirelessly to the AP because the wireless interface of the AP is
usually dedicated to performing the bridging function.
APs operating in bridge mode are popular for creating point-to-point and point-to-
multipoint links.

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WAP 1 acting in root mode
WAP 1
WAP 1 acting in bridge mode
WAP 1
WAP 2
WAP 1 acting in repeater mode
WAP 1
WAP 2
Figure 5-2.  All three operation modes of APs
Repeater Mode
In repeater mode, the WAP extends the reach of the wireless network by repeating
the signals of a remote WAP. The repeater AP can be connected via a hardwire to
the remote root mode AP. Wireless clients can then connect wirelessly to the WAP
operating in repeater mode. This is one of the key differences between the AP repeater
mode and bridge mode. The wireless client node can connect to a WAP repeater, and
wired clients can connect to the WAP bridge. Note that the repeater functionality in
this case should not be confused with the idea of traditional repeater, which generally
involves signal amplification and regeneration.
Implementation of repeater mode in APs is vendor-specific and does not rely on
any IEEE 802.11 standards. Because the implementation of the repeater mode is vendor-
specific, it’s a good idea to make sure that all wireless hardware used comes from the
same equipment manufacturer.

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When to Use a WAP
How does the wireless network administrator know when to use a WAP? Some
guidelines can help answer this question:
■■ The wireless network will span more than three contiguous spaces.
■■ A solid wired network infrastructure is already in place, and the extra services
of multipurpose or multifunction APs are not needed because the existing
wired equivalents will be used.
■■ Wireless switches or controllers will be in use. Other alternatives will not meet
the technical needs or requirements that the WAPs are designed to provide.
Wireless Switches and Controllers
Wireless switches and controllers (WCs) are a class of infrastructure devices for which
there is no ambiguity whatsoever in where they belong or where they are used in
wireless deployments.
WCs are strictly an enterprise class of wireless hardware. They are designed to scale
to meet the needs of different sized networks and serve as a sort of central management
point for other STAs in a wireless network. So instead of your having to configure
or manage WAPs, wireless routers, bridges, and other STAs in a wireless network
manually and individually, you can do it all centrally from the WC. This improves
network management efficiency.
In addition to STA configuration, the following wireless network administration
tasks can be performed via a WC:
■■ Software or firmware management for the STAs (upgrades, downgrades)
■■ The individual configuration or settings for client STAs can be stored or saved
on the WC, making it a configuration repository for client STAs
■■ MAC layer filtering, protocol layer filtering, wireless intrusion detection
capabilities
■■ Quality of service management
■■ Power over Ethernet (PoE) support for remote devices
■■ Authentication and authorization management for connected clients
■■ Dynamic Host Configuration Protocol (DHCP), routing services
■■ AP load balancing management
Figure 5-3 shows a sample wireless controller and various examples of how other
wireless STAs and wired nodes might connect to it in a network.

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WAP 1
WAP 2
SRWR 3
Misc.
hardware
Wireless LAN controller
Figure 5-3.  How wireless STAs and wired nodes might connect to a wireless controller
Wireless Controller Considerations
Wireless controllers are often used in very large wireless networks. A good wireless
network administrator will often intuitively know when one of these devices is
required. Nevertheless, you can use the following to aid in deciding whether or not you
need to deploy a wireless controller:
■■ Sales people from your favorite original equipment manufacturers (OEMs)
keep calling to let you know that you need a controller to go with the 200 APs
you purchased.
■■ You are managing a wireless network whose APs are distributed throughout
different geographical locations.

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After you have determined that a wireless controller is needed on your network,
the following checklist can help you decide which type of controller to purchase:
■■ Choose a controller that implements and supports common standards and
protocols. Devices that implement too many proprietary technologies should
be generally avoided.
■■ If proprietary technologies cannot be avoided, try to stick with hardware
components from the same manufacturers. This can help reduce compatibility
issues that can arise between equipment from different vendors.
■■ Modular controllers should be used whenever possible. This makes it easier to
upgrade and provide support for newer technologies as they are developed in
the future. In other words, it helps to future-proof your hardware investment.
Wireless Routers: SOHO and Residential
Wireless Gateways
Small office home office (SOHO) and residential wireless gateways or routers are
the common folk’s answer to the enterprise-grade WAP discussed earlier. SOHO/
residential wireless routers (SRWRs) are often mistakenly referred to as APs by lay
people, and although they do provide most of the same services that the WAPs offer,
they often provide stripped-down equivalents of the services with smaller footprints.
Note  SRWRs aren’t the only kinds of wireless routers available. Wireless OEMs also
manufacture a wide variety of enterprise-grade pure wireless routers. But SRWRs are the most
prevalent class of wireless routers available today.
Residential gateways normally possess much less processing power (CPU, memory,
and so on) than their enterprise-grade counterparts. But they have enough power to
serve their primary function: to provide wireless and wired nodes in a network access
to another network—the other network usually being a larger network, often a WAN
(such as the Internet). Some routing logic is required in the device before it can link two
or more networks on different subnets. Physically, wireless routers are distinct from
APs because of the presence of a so-called WAN interface.
Wireless routers today provide a plethora of services and can have numerous
features, such as the following:
■■ Support for different security mechanisms, such as MAC layer filtering and
protocol layer filtering via built-in stateful packet inspection (SPI)
■■ Captive portals
■■ Network attached storage hubs
■■ Virtual local area network (VLAN)

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Open Source Alternatives
Several mature and thriving open source communities abound that specialize in
extending the stock features of several SRWRs. Some of the features provided by
these (often free) alternatives are pretty mind-blowing and can make you wonder
whether OEMs are not deliberately crippling their hardware by not shipping or
supporting the features in their own devices out of the box.
You can often improve the feature set of these wireless hardware via software
and firmware upgrades. Some small hardware modifications might be required, but
this is rare. You can find more information about these alternatives at these URLs:
■■ www.openwrt.org
■■ www.freewrt.org
■■ www.dd-wrt.com
■■ www.polarcloud.com/tomato
Although most of these kinds of web sites include standard disclaimers about
using their products on your hardware, you can be assured of the high quality
and usefulness of these alternatives.
■■ Switching functions
■■ Routing functions
■■ Quality of service (QoS) functions
■■ Domain Name System (DNS) server
■■ DHCP server.
It is not uncommon to find SRWRs that can operate in the different WAP modes—
root mode, bridge mode, or repeater mode. In fact, you would be hard pressed to find a
wireless router today that does not support or provide almost all the features listed here.
Wireless Bridge
A wireless bridge is a pretty much a stripped-down WAP operating strictly in bridge
mode. Wireless bridges are dedicated to performing this bridging task and often lack
most of the other bells and whistles that full-functioning WAPs or SRWRs posses. They
are used purely for linking two separate wired network segments together wirelessly.
Wireless bridges are not normally designed to be connected to directly by any wireless
client devices.
These bridges are typically deployed in one of two fashions. First, they can be used
to link two remote sites together wirelessly, which is called a point-to-point (one-one)
link. In this deployment, a clear line of sight (LOS) is normally required between the

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two end points. Second, they can be used to link three or more sites together, which is
called a point-to-multipoint (one-many) link.
In either of these deployment types, one of the bridges acts as the master or root of
the link and the other(s) act as the slave(s) or non-root. The master (root) is the central
and most knowledgeable node in the link. All the other nodes communicate only
through and via the root bridge and not directly with one another.
Note  Another wireless bridge deployment type is used for setting up redundant links or load
balancing traffic between two remote locations wirelessly. To avoid the confusion (loops) that can
occur when more than one path exists for packets while traversing the network, a Spanning Tree
Protocol (STP) mechanism is required. Four or more wireless bridge devices can be combined to
create this deployment. If a failure occurs in one of the links, redundancy is provided because traffic
between the sites can failover to the other good bridge link. Load balancing or load sharing can be
used to specify the type or nature of the traffic that can be transferred over each individual bridge
link. For example, the WLAN administrator can specify that all voice traffic be transferred over one
link, while all non-voice traffic be transferred over the other link.
Power over Ethernet
Power over Ethernet (PoE) is not exactly a type of infrastructure hardware. It is a
technology that is sometimes found implemented in wireless devices used on the
infrastructure side. PoE is also not specifically a wireless-centered technology, and as
such it is not governed by the IEEE 802.11 wireless standards. Instead, it’s described in
a clause in the IEEE 802.3 standard as a method to transfer electrical power, as well as
data, to remote devices over the common twisted-pair cable in an Ethernet network.
Hardware components implementing PoE can be grouped into two types: power
sourcing equipment (PSE) and powered devices (PD).
PoE is especially useful to wireless network administrators because it is often
necessary to position wireless networking equipment (such as APs, wireless routers,
and switches) in awkward locations. One such location might be an unused part of
a building that has no existing electrical wiring or outlet with which to power the
hardware. The idea is that if we can somehow manage to get an Ethernet drop to the
hardware, we can give it power as long as it supports PoE. It might be easier to create
or extend a Ethernet drop instead of creating new electrical wirings and outlets. Using
PoE, we can easily place a wireless STA far up in the ceiling of a warehouse or in the
depths of the Amazonian jungle.
Additional Considerations
When you’re making a decision about which hardware to use in a wireless network
infrastructure, you need to take several other factors into consideration: specifically,
cost and interoperability.

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Cost
Cost is usually a no brainer because, for most of us, financial resources are limited.
Wireless network administrators and managers are required to work within a given
budget range, and a delicate balancing act is involved in keeping wireless network
equipment capital costs down, while continuing to maintain equipment and support
service agreements, staff training, and so on.
Need is probably the most important single driving factor that can affect the decision
of whether to make the equipment purchase or not when budgets are tight. If you need
it, you need it. And if you can do without it, then you don’t need it. Small, medium, and
large businesses these days are trying to run as thinly and efficiently as they can to stay
afloat and profitable.
Interoperability
Interoperability refers to the way some equipment (wireless network hardware in our
case) works with other equipment. It deals with compatibility issues as well, which
may not always be clear-cut. Incompatibilities can stem from the way vendors
(mis)implement the IEEE 802.11 family of standards in their products. It can also result
from an OEM’s desire to corner a certain market segment by deliberately making its
hardware and the protocols used proprietary.
Interoperability issues can also arise for completely innocent reasons, such as
when you’re trying to work with legacy equipment or protocols. It is not often that
the wireless administrator or network designer has the opportunity to design or work
with a brand new network from scratch. We often have to deal with and accommodate
existing or old hardware and clients.
The only way to mitigate most interoperability issues is by careful planning and extensive
testing before deploying infrastructure-type hardware. A lot of real-world snafus can be
discovered during testing, and this will ultimately aid you in making the right decision.
Summary
Infrastructure-side wireless hardware includes a variety of hardware that might be difficult
to categorize as client- or infrastructure-side hardware. When this hardware is used on
the client side (such as the antenna), it can be quite nondescript (and taken for granted),
but you know that it plays an important role nonetheless in any wireless communications
system.
Some hardware is clearly used only on the infrastructure side of a wireless network.
Various categories of hardware can aid connectivity and provide one service or the
other to other wireless STAs or wired nodes in a network. You need to consider several
important factors when dealing with infrastructure hardware, which were covered in
this chapter. You also learned about PoE, a technology that allows you to power any
supported wireless networking equipment almost anywhere.

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Part III
WLAN, WWAN, WMAN,
and WPAN

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Key Skills and Concepts
■■ Define common wireless local area network (WLAN) terminologies.
■■ Examine the key components of a WLAN.
■■ Understand the IEEE 802.11 standard governing WLANs.
■■ Understand the physical and Media Access Control (MAC) components of
IEEE 802.11.
Alocal area network (LAN) spans a relatively small physical area—relatively small,
because the area can be the size of a closet, a room, a home, an entire office, or
  a group of buildings. Compared to a wide area network (WAN), such as the
Internet, and a metropolitan area network (MAN), a LAN seems pretty small. Several
LANs can be used to make up the much larger networks of WANs and MANs.
A WLAN is a type of LAN technology. In fact, the IEEE 802.11 standard that governs
the basic operations and functions of WLANs says that a WLAN is required to appear to
higher protocol layers as a regular wired IEEE 802 LAN.
WLAN Components and Concepts
WLANs comprise several components, some purely logical and others physical. The
following sections introduce some of the components that make up a WLAN and
define some of the lingo used in describing the entities in a WLAN.
Wireless Medium
The wireless medium (WM) is used for the actual transfer of information between the
entities of a WLAN—that is, air and space.
Various types of data can be encoded into a type of electromagnetic disturbance
called radio waves. These radio waves are then transmitted over the air (our medium)
to their destination, where they are decoded back into useful data.
Wireless Station
Any device that implements the IEEE 802.11 standard is called a wireless station (STA).
A STA is therefore a single physical entity that can perform the 802.11 song and
dance. Wireless STAs are not very useful by themselves; they need other wireless or
wired devices to send information to and receive information from in order to make
them useful.
Figure 6-1 shows some sample wireless STAs.

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Smartphone
Workstation
Laptop
AP
Tablet
STA
STA
STA
STA
STA
Printer
STA
Figure 6-1.  Sample STAs
A STA can operate in one or more of the following modes:
■■ Infrastructure mode  Also referred to as client mode STA, this mode
requires the use of an infrastructure device, such as an access point (AP), for
communicating with other STAs, as well as with the wired LAN. Devices
operating in this mode can be considered wireless clients, which implies that
the wireless STA acts as a client in a WLAN. Other literature may refer to client
mode STAs as mobile units (MUs). Despite the name, MUs can, of course, be
either mobile or in a fixed location. Infrastructure mode is probably the most
typical and common mode of operation for the vast majority of wireless devices.
■■ Ad hoc mode  Ad hoc STAs form autonomous networks that do not require
an AP to communicate with other STAs. They can be either mobile or in a fixed
location.
■■ Access control mode  As implied by the name, an access control STA is used
for controlling access between STAs or controlling STA access to the wired
LAN. A wireless access point (WAP) is a good example of a STA that operates
in this mode.
Distribution System
The distribution system (DS) is an important part of any network and serves as a “glue”
for interconnecting similar or dissimilar networks together.
The fabric of the DS can be based on any of the common wired technologies such
as Ethernet. It can also be entirely wireless using regular wireless technologies such as
those based on IEEE 802.11.
In wireless networks, the DS can be used for linking the wireless STAs to the wired
resources. In fact, the most common use of the DS is for bridging a wireless network to
the wired network.

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Access Point
The access point (AP) is a type of STA. Specifically, it helps link wireless stations to the
wired stations or resources, or it may simply be used for connecting wireless STAs to
one another.
Basic Service Set
The basic service set (BSS) is a logical entity in a WLAN. The BSS can also be viewed
as a type of WLAN topology. BSSs come in two “official” types: independent BSS and
infrastructure BSS.
A third, but “unofficial,” topology type exists, called a wireless distribution system
(WDS). It’s unofficial because it is not officially sanctioned or described in the 802.11
specification, and neither is it sanctioned by the Wi-Fi Alliance special interest group.
But it is widely used in WLAN setups.
Infrastructure BSS
Infrastructure BSS, frequently referred to simply as a BSS, makes use of an AP. Most
WLANs operate in this mode. The STAs that participate in the infrastructure BSS do
not communicate directly with each other; all communications go through the AP.
The IEEE 802.11 standard defines the BSS as “a set of stations (STAs) that have
successfully synchronized amongst themselves using the appropriate functions.” These
functions are called primitives in the 802.11 technical jargon.
Infrastructure mode STAs operate in infrastructure BSS. The following illustration
shows a sample infrastructure BSS:
Laptop STA
Workstation
STA
STAs
Tablet STA
AP
Printer STA

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Independent BSS
The Independent BSS (IBSS) does not make use of an AP; the STAs communicate directly
with one another in a peer-to-peer fashion. A minimum of two STAs are required to
form an IBSS.
Ad hoc mode STAs operate in IBSS mode. The following illustration shows an IBSS:
Wireless Distribution System
Wireless distribution systems (WDS) are used to describe WLAN topologies in which
APs are connected together. Strictly speaking, it means that the infrastructure devices
(or APs) are linked together using a wireless medium (air or space) as the distribution
system. A WDS is used for creating a wireless backbone link between the APs in a
WLAN. This is in contrast to the traditional method of linking the APs in a wireless
network via a wired distribution system.
The WDS often requires that all participants employ and share various characteristics,
such as a common radio frequency (RF) channel and a common security mechanism.

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The next illustration shows a sample WDS.
STA
STA
AP
STA
STA
AP
STA
Service Set ID
The service set ID (SSID) is used to identify an extended service set (ESS) or IBSS.
Specifically, it is a human-friendly means of identifying the ESS or IBSS. The SSID is
the name that users often see when they are presented with a list of available wireless
networks detected by their wireless device.
The SSID can be 0 to 32 bytes long.
Basic Service Set ID
It only makes sense that if we have a human-friendly way of identifying wireless
networks, we should also have a machine-friendly way of doing the same thing. This
is the job of the BSSID, which is used for identifying each BSS. It is 48 bits long and is
very similar to the MAC address used on Ethernet-based networks.
The exact value of the BSSID depends on the service set in use (Infrastructure or
Independent).
In the Infrastructure BSS, the BSSID is easily determined, because it is the MAC
address currently in use by the wireless STA that is acting as the AP. Recall that the
Infrastructure BSS always has an AP present. This MAC address is a universally
administrated type, and it is always bound to be unique. A sample BSSID for an
infrastructure BSS is 00:ab:34:56:78:9a.
In the ad hoc, or independent mode, BSS, the BSSID is a locally administered (non-
universally unique) type of MAC address. A locally administered MAC address is one
in which the value of universal or local (U/L) field bit is set to one (1). Specifically
this means that the second least significant bit of the most significant byte of the MAC
address has a value of one (1). The first byte is then followed by a 46-bit randomly
generated number. A sample BSSID for an ad hoc network would be 02:12:34:56:78:9a.

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Basic Service Area
The basic service area (BSA) defines the physical area or boundary spanned by any BSS.
It is used to describe the physical area containing the members of a BSS. This area may
also span other BSSs, which means that it may contain members of other BSSs.
Extended Service Set
The IEEE 802.11 standard defines an extended service set (ESS) as “a set of one or more
interconnected basic service sets (BSSs) and integrated local area networks (LANs)
that appears as a single BSS to the logical link control (LLC) layer at any station (STA)
associated with one of those BSSs.” The LLC is a data communication protocol sublayer
in the OSI reference model. Specifically, it is a sublayer of the Data Link layer. (More
about the OSI in the following section.)
An ESS is normally a union of BSSs, but the foundation for the ESS is laid as soon as a
BSS is born. This means that the mere existence of a BSS implies the existence of an ESS.
The following illustration shows a sample ESS; it also shows the relative positions
of some of the components of WLANs that have been discussed thus far.
Client STA
STA
BSS
Client STA
DS
AP
AP
Client STA
BSS
STA
WLAN Standard (IEEE 802.11)
As you know, the IEEE 802.11 is a family of standards that governs the operations and
functions of WLANs. But the standard does not define or manage absolutely every
aspect of WLAN operations—it specifically concerns itself only with the functions of
WLANs at the Physical (PHY) layer and Media Access Control sublayer of the OSI
reference model. We examine these functions next.
Figure 6-2 shows the entire OSI model.
PHY
The Physical layer is the first layer (Layer 1) in the OSI reference model. It defines the
relationship between a device and the physical communication medium.

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OSI Model
Application
Presentation
Session
Transport
Network
LLC sublayer
Data Link
MAC sublayer
Physical
Figure 6-2.  OSI reference model
For our purposes, a good example of the device is any IEEE 802.11 compliant
hardware, and the physical communication medium is the airspace.
The PHY layer for IEEE 802.11 specifies the wireless signaling techniques used for
transmitting and receiving information over the airwaves. Sample signaling techniques
are listed in Table 6-1.
The PHY layer provides service to the IEEE 802.11 MAC sublayer, which is
discussed next.
Note  Various countries’ regulatory bodies are dedicated to controlling and managing how the
PHY layer of wireless devices is implemented. Wireless network administrators and other end
users must therefore ensure that their wireless devices are properly configured and used so that
they do not violate local laws governing the transmission and reception of RF signals. By the same
token, manufacturers of wireless devices must also make sure that their devices are designed and
properly labeled for use within a given region without violating the local radio spectrum use laws.
See Chapter 1 for more information about radio spectrum use regulations.

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Signaling Technique
Explanation
Frequency-hopping spread
spectrum (FHSS)
This signaling (modulation) technique specifies use in
the 2.4 GHz industrial, scientific, and medical (ISM)
frequency band.
The specific frequency range is 2.402–2.480 GHz.
FHSS works by making the signals hop (or jump
from one to another) through the allowed frequency
channels in a predetermined sequence. For example, a
predetermined sequence can be as simple as saying that
every 5 seconds the system will hop to a new channel
within the ISM frequency ranges.
FHSS is one of the modulation techniques used in early
WLAN implementations and is rarely used today. It
supports data rates of 1–2 Mbit/s.
Direct-sequence spread
spectrum (DSSS)
This signaling (modulation) technique specifies use in
the 2.4 GHz ISM band.
The specific frequency range is 2.400–2.497 GHz.
Systems implementing this PHY can support 1 Mbit/s
and 2 Mbit/s data rates.
High rate direct sequence An extension or enhancement of the DSSS PHY. It also
spread spectrum (HR/DSSS) operates in the 2.4 GHz ISM frequency bands.
Systems implementing this PHY can provide data rates
of 1, 2, 5.5, and 11 Mbit/s.
Orthogonal frequency
division multiplexing
(OFDM)
Specifies use in the 5 GHz Unlicensed National
Information Infrastructure (UNII) frequency bands and
the 2.4 GHz ISM bands. Most of the recent IEEE 802.11
standards implement this PHY and its variants.
Compared to the other PHYs, OFDM generally
supports higher data rates. Systems implementing this
PHY can support 6, 9, 12, 18, 24, 36, 48, and 54 Mbit/s
data rates.
(Continued )
Table 6-1.  Signaling Techniques

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Signaling Technique
Extended rate
PHY (ERP)
Explanation
The ERP PHY specification is actually several PHY
specifications in one. It provides extensions to the
existing PHY specifications, such as DSSS and OFDM.
The extensions are intended to enhance backward-
compatibility and coexistence with existing PHYs. It
operates in the 2.4 GHz frequency band.
Some popular variations of ERP are:
ERP-DSSS  Provides support for systems that need to
implement the ERP PHY but also need to be backward-
compatible with DSSS PHY.
ERP-OFDM  Implements the OFDM PHY purely for
operation, in the 2.4 GHz band. Systems implementing
this PHY can support 6, 9, 12, 18, 24, 36, 48, and
54 Mbit/s data rates.
DSSS-OFDM  Provides a mixed mode (or hybrid)
operation for DSSS and OFDM systems. Older DSSS
systems can interpret parts of the communication (such
as the header) and the newer OFDM-based systems can
interpret the header and the actual data payload parts
of the communication.
Table 6-1.  Signaling Techniques (Continued )
MAC
To maintain some semblance of sanity in data communications (and human
communications), certain rules and guidelines must be established and followed.
This is especially important in wireless communications because of the nature of the
medium used for the communications—air or space. The rules and guidelines are
specified at different layers of the OSI model.
MAC is a sublayer of the OSI’s Data Link layer, or layer 2. The MAC sublayer
is basically responsible for providing addressing and medium access control
mechanisms that make it possible for several nodes to communicate in a network.
The MAC functions are used to control and manage access to the transmission
medium in a communications system.

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Controlling the access of stations plugged into a wired Ethernet LAN (IEEE 802.3)
is relatively simple because of the use of cables. All nodes plugged into the same
network can easily sense the presence or absence of an electric current in their cables.
The electric current here implies the data transmission. To coordinate access to the LAN
medium, LAN stations use Carrier Sense Multiple Access with Collision Detection
(CSMA/CD). The key word here is “detection.”
The rules that govern the IEEE 802.11 WLANs can not easily piggyback off this same
method for managing access to the shared medium used in wired LANs. And there are
several reasons behind this—one reason is the absence of physical wires.
The STAs in a wireless network cannot always be guaranteed to be within earshot
of each other so that they can hear (or detect) when the other STAs are transmitting.
This phenomena is known as the “hidden node” problem in RF communications.
Furthermore, the transmission may not even be meant or destined for the hidden node,
but it still needs to use the common transmission medium shared by all the nodes.
The second reason is because the radio in most wireless LAN hardware is capable
of operating in either a transmitting or receiving mode at one time—it can’t usually do
both at the same time. For the wireless hardware to be able to detect collisions (receive
mode) while it is sending data (transmit mode), it needs to include a radio that offers
such capabilities. And as has already been mentioned, this is not the case in commodity
wireless LAN hardware.
So instead of attempting to detect when the medium is available for use, 802.11-
based systems take a different tack by trying to avoid any type of collision in the first
place. This is Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA), and
the key word here is “avoidance.”
A popular method for implementing CSMA/CA in wireless LANs is known as
the Distributed Coordination Function (DCF). The following steps show how three
sample wireless STAs (STA-a, STA-b, and STA-c) might negotiate access to the wireless
medium. Note that this is only one of the several methods by which CSMA/CA can be
implemented.
1. STA-a needs to access the wireless medium, so it puts its radio in receiving
mode to see if any other STAs are currently transmitting anything.
2. If STA-a sees that the medium is in use by STA-b, it waits until STA-b is done
with its transmission. The amount of time that STA-a waits is determinate.
3. STA-a will attempt to transmit again by first checking to see if the medium is
available. If so, STA-a will send out a special MAC frame called a Request To
Send (RTS) frame. Also called a control frame, this is one of several MAC frame
types (as discussed in the next section).
4. STA-c will see the special frame sent from STA-a and in turn send a Clear To
Send (CTS) frame.
5. STA-a will send its message to STA-c.

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6. For the communication to be considered successful, STA-c needs to send
an acknowledgement confirming that it indeed received the message sent
by STA-a. This message is carried in another control frame type called an
Acknowledgment (ACK) frame. This is also known as positive acknowledgement.
7. If, for whatever reason, STA-a does not receive an ACK message from STA-c, it
resends the message.
MAC Frame Types
Depending on their function, IEEE 802.11 MAC frame types can be grouped into three
categories: control frames, management frames, and data frames.
Control Frames  These most basic frame types are very important for all WLAN
communications and are used to support the delivery of the other (management and
data) MAC frame types. All the wireless STAs must be able to see the control frames—in
other words, the information in the control frames is not secret or classified in any way.
Control frames are used, for example, when a wireless STA needs to negotiate
and gain access to the WLAN using CSMA/CA. Other types of control frames are the
Request to Send (RTS), Clear to Send (CTS), and Acknowledgment (ACK) frames.
■■ RTS  Provides some collision avoidance mechanisms for WLANs—a way to
check whether the communication medium is in use by other STAs
■■ CTS  Sent by STAs in response to the RTS frame
■■ ACK  Sent by the receiving STA to confirm successful reception of the frame
in question
Management Frames  These frame types are used for management purposes on the
WLAN, where they play a very important role. Management frames are used by
wireless STAs whenever an STA officially wants to participate or discontinue its
participation in the network and for other miscellaneous housekeeping purposes. Here
are some sample management frame types:
■■ Beacon frame  A very important management MAC frame type, it performs
various functions, such as time synchronization among the STAs; it also stores
the value of the SSID, specifies the PHY being used, and specifies the data rates
supported on the WLAN, among other things.
■■ Association Request frame  These frames are sent by the STA to request
association with the AP.
■■ Association Response frame  These frames contains the AP’s response to the
STA regarding the STA’s association request. It is either a yea or nay.
■■ Reassociation Request frame  These frames are used by STAs whenever they
need to be reassociated with an AP.
■■ Reassociation Response frame  These frames are sent by the AP in response
to the STAs request to reassociate with the AP.

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■■ Authentication frame  These frames are used whenever a STA needs to
participate in or join a BSS. Mere association is not nearly enough—the
STA needs to be authenticated to make full use of the BSS. The STA uses
authentication frame types to confirm its identity.
■■ Deauthentication frame  Authenticated STAs use these frame types to signal
their intention to terminate the authenticated (secure) communications.
■■ Disassociation frame  This frame is sent by a STA that is associated with an
AP to inform the AP that it wants to discontinue the association. Note that this
is not a request, and as such a response or acknowledgment or confirmation is
not required from the AP.
■■ Probe Request frame  STAs send probe request frames whenever they need
to discover information about other STAs. Such information might include the
capabilities of the other STA or information about the supported data rates.
■■ Probe Response frame  This frame carries the response to probe requests.
Data Frames  These frame types are responsible for transporting the actual data
payload to and from the communication end points.
Complete MAC Frame
The following illustration shows a typical 802.11 MAC frame format. Table 6-2 explains
some parts of the MAC frame that might be interesting from the perspective of a wireless
network administrator.
MAC Header Frame
Header
Data payload
CRC-32
Frame Duration & Address Address Address Seq Address Qos Frame
control
ID
1
2
3
control
4
control body
FCS
Protocol
version
Type
Sub-
type
To DS
From
DS
More
frag
Retry
Power
management
More
data
Protected
frame
Order

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Field
Description
Frame Control
Address 1
Address 2
Address 3
Address 4
Sequence
Control
Frame Body
Duration/ID
Frame Check
Sequence (FCS)
Power
Management
Holds important information. Divided into several fields. Sample
information stored with the frame control field is related to protocol
version in use, frame type (control, management, or data), fragmentation
information, power management, etc.
Can be any of the following types:
Source Address (SA)  A 48-bit MAC address. Serves the same purpose as
the layer 2 source address used on Ethernet networks. It is the address of
the STA that created the original frame to be transmitted.
Destination Address (DA)  A 48-bit MAC address. Serves the same
purpose as the layer 2 destination address used on Ethernet networks. It is
the address of the final recipient of the IEEE 802.11 frame.
Receiver Address (RA or Rx STA)  May or may not be the same as the
final destination address (DA). May be the address of the next hop radio
device on the WLAN that will forward the packet to its final destination.
In an infrastructure BSS that uses an AP for all communication, RA is often
the same as the BSSID—such as when the SA is relaying frames to AP for
transmission.
Transmitter Address (TA or Tx STA)  A 48-bit MAC address. May or may
not be the address of the STA that generated the original frame. TA may
be an intermediate STA that transmits the frame. In an infrastructure BSS
that uses an AP for all communication, TA may also correspond with the
BSSID—such as when the AP is relaying frames back to the SA.
Contains the fragment (of the specific fragment in question) and sequence
numbers (of each frame).
Contains the actual data to be sent. If no data payload is to be sent, the size
of this field will be 0, which is the case when the frame type is a control
frame, for example.
Used by wireless LAN devices to reserve or specify the time period for
which RF medium will be in use.
Used for checking or verifying that the frame in question did not get
corrupted during transmission, using cyclic redundancy check (CRC).
Used to indicate the power management mode of a STA. Shows the mode
of the STA after a successful completion of the frame exchange sequence.
A value of 1 indicates that the STA will be in a power-saving mode.
And a value of 0 means that the STA will be in active mode. For frames
transmitted by APs, this field is always 0.
Table 6-2.  Fields of an IEEE 802.11 MAC Frame

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Field
Description
Protected
Frame
Used to indicate when the frame body field contains information that has
been processed by a cryptographic algorithm. A value of 1 means that
frame body field is encrypted. A value of 1 is possible only within data
frame types and some management frame types. A value of 0 is used for all
other frame types.
More Data
Used as an indicator that more data is on the way. Tells a STA in power-
saving mode that more data is buffered and on its way.
More Fragments Used to indicate when more data fragments are to follow.
Retry
Receiving wireless STAs use this field to prevent processing of duplicate
frames. A value of 1 in a management or data frame means that the frame
is a retransmission of an earlier frame. The value is set to 0 for all other
frame types.
Protocol
Version
This field is 2 bits in length. As at the time of this writing, the protocol
version number for the IEEE 802.11 standard is 0. All other possible values
for this field are reserved for major changes in the current standard. The
revision level will be incremented when a fundamental incompatibility
exists between a new revision and a prior edition of the standard.
Type and
Subtype
Identifies the specific function of the frame.
To DS and
From DS
To Distribution System and From Distribution System.
The meaning of these fields varies depending on the combined values
in the fields. The possible values are 1 and 0, which can be combined to
mean the following:
To DS = 0 and From DS = 0
Implies that the frame has been sent from one STA to another STA within
the same IBSS (as in ad hoc) networks. Indicates a frame sent from a non-
AP STA to another non-AP STA within the same BSS.
To DS = 1 and From DS = 0
Implies that the frame is destined for the DS or a frame being sent by a STA
associated with an AP.
To DS = 0 and From DS = 1
When the two fields are set with these values, it means that the frame in
question is exiting the DS.
To DS = 1 and From DS = 1
The frame uses the four-address format. This combination is possible but is
currently not defined in the IEEE 802.11 standard.
Table 6-2.  Fields of an IEEE 802.11 MAC Frame

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Summary
This chapter provided an inside peek into the fabric of IEEE 802.11-based networks, which
can help you to understand and troubleshoot odd or complex wireless connectivity issues
later on. You learned that the IEEE 802.11 family of standards guides WLAN technologies.
Some concepts and terminologies are used in everyday WLAN discussions, and
you need to know these concepts and terms to understand the IEEE 802.11 standard.
The main components of the IEEE 802.11 standard are the Physical layer and the
MAC sublayer of the OSI reference model. In the Physical layer of the WLAN standard
are some specific PHY implementations, such as DSSS, FHSS, OFDM, and ERP.
In the MAC sublayer, you learned about the functions and different parts of a
typical MAC frame.
This chapter is by no means a complete dissection of the WLAN standard as defined in
IEEE 802.11. The inner workings of the current standard itself are included in a document
that is almost 1300 pages long! This may seem daunting, but interested readers should
rest assured that the IEEE 802.11 standard contains a lot of repetition of the same basic
concepts applied to different facets of the standard.
Nevertheless, the information provided in this chapter should serve as a springboard
for you as you dive into the IEEE 802.11 standard proper. Some of the subsequent
chapters in this book cover certain aspects of the IEEE 802.11 standard in varying details.

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Key Skills and Concepts
■■ Learn about wireless wide area networking technologies.
■■ Learn about wireless metropolitan area networking technologies.
■■ Learn about wireless personal area networking technologies.
Very few rules and standards apply to wireless wide area networks (WWANs),
wireless metropolitan area networks (WMANs), and wireless personal
area networks (WPANS), and we have very little control over our data or
communications. This chapter offers information about these networks, including any
applicable standards, incarnations, components and architecture, special features, and
special interest groups (SIGs). Note that the information in this chapter is by no means
a complete or thorough coverage of these technologies, but it highlights the features
that you, as a wireless network administrator, might find especially interesting.
Wireless Wide Area Networks
A WAN can span a large geographical area—a country, multiple countries, and even
continents. The Internet is a classic example of a WAN. A Wireless Wide Area Network
(WWAN) is a class of WAN technologies that uses mostly cellular and satellite
infrastructures to enable interconnectivity over a WAN via several services, such as
Global System for Mobile (GSM) communication and several incarnations of GSM, the
Universal Mobile Telecommunications System (UMTS), and Long Term Evolution (LTE).
Note  A wireless network administrator may not have much control over the type of hardware
and other implementation details of WWANs in use at his or her site, because these things are often
determined by third-party service providers. However, the information about WWAN is included in
this chapter because you’ll find it useful to understand the technologies powering your networks.
This knowledge can, for example, help when you’re selecting or negotiating with service providers
that will implement the actual technologies. It can also help in integrating these WWAN technologies
with the existing network infrastructure that you control.
GSM Overview
GSM is a widely used digital cellular voice and data service that was initially conceived
as standard that could be readily adopted by different countries and existing standards.
And it has met and surpassed this initial requirement, because GSM is now adopted as
a base standard in more than 80 percent of the world’s mobile phone market.
GSM is considered a second generation (2G) cellular technology. The ability of
wireless client devices to be truly mobile is a distinguishing feature of the 2G cellular
technologies.

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True mobility was made possible by the use of cells in mobile network designs.
A cell is simply an imaginary boundary within which wireless radio frequency (RF)
coverage is managed and provided by a base station. The grouping of various and
consecutive cells is where the name “cellular” comes from. Various cells working
in conjunction to provide expanded and seamless RF coverage to a wireless client
provides mobility for the client.
Various GSM network operators own and manage their own cells, and these
network operators often use sharing (also known as roaming) agreements that allow
users to use their mobile devices anywhere GSM coverage is available—all at a cost, of
course.
Figure 7-1 shows the relationship of the cells in cellular network and a wireless
client device. Part A of the figure shows how mobility can be restricted to areas around
the single cell tower. Part B shows how mobility can be enhanced when more cells are
added to the scenario and mobile users can roam between cells.
Part A
Part B
Figure 7-1.  Relationship of cells in a cellular network and wireless client device

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Second-generation GSM networks operate in the 900 MHz and 1.8 GHz frequency
bands in Africa, Australia, Europe, Middle East, and Asia (excluding Japan and
South Korea), and parts of South America. They operate in the 850 MHz and 1.9 GHz
frequency bands in North America, Latin America, and parts of South America. A more
complete map of the GSM frequency bands in use in every country can be found at
www.worldtimezone.com/gsm.html.
GSM Components and Architecture
GSM networks comprise several components: a mobile station (MS), a base station system
(BSS), and a network switching system (NSS).
Mobile Station  The MS is the one part of the GSM network over which the user has some
control (to the extent that the user is allowed to choose the color and sometimes ringtone
of the wireless device). This is the part that can sometimes cost a lot of money, too. It
includes any wireless client device that we intend to connect to the operator-controlled
GSM network. Good examples of a MS are cell phones or a WWLAN adapter card
connected to a laptop. The MS talks to the BSS (discussed next).
Every MS is uniquely identified by a International Mobile Equipment Identity
(IMEI) number that is hard-coded into the GSM client device and therefore not easily
transferable between devices. Among other details, the IMEI number describes the
organization that registered and allocated the unique IMEI number, the model, and the
vendor-assigned serial number of the GSM device.
The first time a user subscribes to the services of a GSM network operator, he or she
is issued a Subscriber Identity Module (SIM) card. The SIM card is a type of smart card
that stores information designed to identify a user or account uniquely on any GSM
network. The SIM card is tied to the user but is portable between devices. The SIM card
stores the International Mobile Subscriber Identity (IMSI), the current subscription
information, user authentication data, and a simple contact database for the user (an
address book). The IMSI is unique world-wide.
Base Station System  The BSS component of a GSM network is an amalgamation of
components owned and managed by the network operator. It usually comprises
the base station controller (BSC) and the base transceiver stations (BTS)—the radio
transmitters, receivers, and antennas that serve each cell.
The BSC is the brains behind the BTS. It stores the configuration data used for
managing the BTS. For example, it controls the RF power levels in the BTS, which in
turn connects the cell to the NSS, from which it gets its own instructions.
The MS connects to the BSS which in turn connects to the Network Switching
System, discussed next.
Network Switching System  The NSS is a central component of any GSM infrastructure.
It comprises several parts that perform different complicated functions, such as call
processing, subscriber-related functions, and interfacing the mobile phone network
with the traditional Public Switched Telephone Network (PSTN).

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GSM SIGs
The Third Generation Partnership Project (3GPP), one of the major GSM SIGs, is
committed to the maintenance and development of GSM’s technical specifications
(www.3gpp.org). It does this by helping to unite various telecommunications standards
bodies all over the world.
Another GSM SIG, the GSM Association (GSMA) represents the interests of the
mobile communications industry all over the world (www.gsmworld.com). Its focus is
to drive the growth of the mobile communications industry by helping to develop and
create new opportunities for its members (manufacturers and suppliers of GSM-based
technologies). Its objective is clearly different from that of the 3GPP, which is more
concerned with standards issues.
GSM Incarnations
The original GSM standard has undergone many evolutions and revisions—too many
to mention them all here. One standard, General Packet Radio Service (GPRS), is of
particular interest to us as wireless network administrators. It was designed to handle
data and other multimedia applications, unlike the 2G technologies, whose focus was
mainly voice applications.
GPRS  GPRS is a standard used for communicating over cellular networks. It is often
referred to as a two-and-a-half–generation (2.5G) cellular technology. GPRS is based on
packet-switching, which offers several advantages from the perspective of a wireless
mobile user interested in wireless data communications. One such advantage is cost—
packet-switched services are generally cheaper than their circuit-switched counterparts,
and billing is often based on the amount of actual data transferred. Packet-switched
networks allow the communication medium to be shared among different users,
so no expensive circuits need to be dedicated to the user. This sharing can also be
a disadvantage, however, because a fixed bandwidth is not always guaranteed or
available to individual users.
From the perspective of the wireless network administrator, GPRS-based devices
can support the following features:
■■ Internet Protocol (IP) versions 4 and 6
■■ Wireless Application Protocol (WAP)
■■ Data transfer rates of 56–114 kbit/ps
GPRS can be used for data communications in a wide variety of devices, such as
mobile phones, GPRS expansion cards for laptops or personal computers, and remote
terminals such as point-of-sale systems.
When used for data communications, GPRS-based devices make extensive use of the
notion of an Access Point Name (APN), a simple and distinct name that is meaningful
only within the cellular service provider’s network. The APN is distinct from access points
(APs) used for purely WLAN communications, but, generally speaking, they both help to
provide wireless clients access to resources available on a network.

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The APN used in GPRS services specifies the external network or services that a
wireless mobile device can access. These are usually one of two types: WAP APNs or
Internet APNs.
The WAP APN provides access to the mobile provider’s WAP content, which is often
filtered and reformatted to meet WAP specifications. A sample WAP APN for a cellular
service provider named Wireless WANS ‘R’ US 1234, Inc., could be wap.wwrs1234.com.
The Internet APN provides the mobile device access to the standard Internet-based
services such as e-mail and web browsing.
A sample Internet APN for a cellular service provider named Wireless WANS ‘R’
US 1234, Inc., could be internet.wwrs1234.com.
UMTS Overview
The Universal Mobile Telecommunications System (UMTS) is a third-generation (3G)
cellular standard that has several implementations that go by different monikers or
brands. Example UMTS implementations are Freedom of Mobile Multimedia Access
(FOMA) and Wideband Code Division Multiple Access (W-CDMA).
The BTS component of 2G GSM networks is replaced by a new component called
Node B in 3G UMTS networks. The functionality provided by the BSC in 2G GSM
networks is provided by a component called the Radio Network Controller (RNC) in
UMTS.
UMTS SIG
The UMTS Forum (www.umts-forum.org) can be considered a UMTS SIG with very
clear objectives. The Forum’s objective is to help all UMTS stakeholders understand
and profit from the opportunities of 3G/UMTS networks.
UMTS Incarnations
The next sections discuss some revisions and enhancements to the original UMTS
standards. Some of these revisions are the High Speed Packet Access (HSPA) family
of technologies, such as High Speed Downlink Packet Access (HSDPA), High Speed
Uplink Packet Access (HSUPA), and HSPA Evolved (eHSPA)—aka HSPA+. The
revisions are referred to as UMTS releases.
HSPA Overview  HSPA refers to a family of WWAN mobile technologies that provides
mobile broadband access for GSM-based devices. HSPA is considered a post-3G
cellular technology. It was specifically designed to offer an easy upgrade path for
cellular network operators who want to deploy the post 3G technologies. HSPA-based
networks operate in the 850, 1900, and 2100 MHz frequency bands.
High Speed Downlink Packet Access  HSDPA is a 3G cellular technology based on the
UMTS standard. It is described in the UMTS standard Release 5. Among its other
features, HSDPA offers improvements in the downlink speeds of its predecessor
(HSPA), with downlink speeds of 14 Mbps.

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High Speed Uplink Packet Access  HSUPA is a 3G cellular technology described in the
UMTS standard Release 6. It is referred to simply as Enhanced Uplink (EUL) in some
quarters.
Among its other features, HSUPA offers improvements in the uplink speeds of its
predecessor (HSDPA), with uplink speeds of 5.7 Mbps.
HSUPA also supports WLAN integration.
The coverage offered by WLANs is traditionally limited and best suited for indoor
use, but the coverage offered by a UMTS network can span several miles and is best
suited for outdoor use. The strengths and weaknesses of these two technologies can be
used to complement one another.
This particular feature makes it possible for mobile stations (such as cell phones)
to use either the cellular provider’s managed WWAN or the user-managed WLAN to
make voice calls or for data communications. So, for example, when a user is within the
reach of a WLAN or Wi-Fi signal, all voice and data communications can occur via a
traditional wireless access point (WAP) or residential gateway router. The possibilities
and uses of this feature are many (and, of course, can cause headaches for the wireless
network administrator).
HSPA+ Evolved  HSPA+ (pronounced HSPA plus), often referred to as HSPA Evolved
(eHSPA), is a 3G cellular technology that is described in the UMTS standard Release 7.
Among the many enhancements it offers, HSPA+ is purported to be capable of
theoretical downlink speeds of 42 Mbps and uplink speeds of more than 11.5 Mbps.
The Multiple Input/Multiple Output (MIMO) antenna technology is used to achieve
the enhancements in HSPA+.
LTE Overview
LTE is GSM on steroids. The authors and backers of LTE describe it as an evolution of
the 3G/HSPA cellular technologies. LTE is designed to be backward-compatible with
GSM and HSPA technologies. “Improved spectral efficiency” is one of the strong points
touted about LTE, which simply means that the technology can make more efficient use
of the available radio spectrum.
LTE Special Features
LTE is purported to be capable of theoretical downlink speeds of 172 Mbps and uplink
speeds of more than 50 Mbps. It will make it possible to deliver rich multimedia and
bandwidth-intensive applications over long distances wirelessly.
LTE is a purely IP-based technology.
LTE SIGs
Almost everybody in the wireless community has interests in the success of LTE—
from the network operators (who can make more money with less resources), to the

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equipment manufacturers (who can charge more for cool new hardware to support the
technology), to the consumer (who pays more for the cool new hardware and for access
to the better network).
LTE is a highly anticipated technology that is supposed to be a win-win situation
for most stakeholders.
Wireless Metropolitan Area Networks
A MAN can span a moderately large geographical area. The scope of the area covered
by a MAN is often within a city but almost certainly restricted to within a country.
A WMAN refers to wireless technologies that facilitate interconnectivity wirelessly
in a metropolitan area. WMANs can be considered mid-range networks. They normally
do not use the cellular network infrastructure, but instead make use of some vendor-
specific technology.
In some cases, the wireless network administrator may not have much control over
the type of hardware and other implementation details of WMANs in use at his or
her site, because these aspects are often in the hands of third-party service providers.
However the information is included here because it is useful for you to understand
the technologies powering those networks. This knowledge can help, for example,
when you’re selecting or negotiating with service providers that will implement the
actual technologies. It can also help you in integrating these WMAN technologies with
an existing network infrastructure.
In the next section we’ll look at one specific technology called WiMAX that is used
in building WWAN networks.
Note  WMAN can also be built by wirelessly connecting two or more WLANs using IEEE 802.11
standard-based equipment and protocols.
WiMAX Overview
Worldwide Interoperability for Microwave Access (WiMAX) is used in building WMAN
networks. WiMAX can serve as a capable “last mile” technology, which means that it can
be used to bypass the traditional cable or wired infrastructure to provide connectivity
between the communications provider and the customer.
WiMAX operates in the 2–66 GHz frequency range.
WiMAX Standards
WiMAX is governed by the details specified in the IEEE 802.16 standards, where it’s
called WirelessMAN. Of the several revisions and versions of the standard, two are
especially interesting to us here: IEEE 802.16d and IEEE 802.16e.

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WiMAX Incarnations
Two incarnations of the standard are important to wireless network administrators:
Fixed WiMAX and Mobile WiMAX.
■■ Fixed WiMAX  This first mainstream version of WiMAX was widely adopted.
It is especially suited for point-to-multipoint (one-many) applications. Its inner
workings are specified in IEEE 802.16d.
Fixed WiMAX is purported to support wireless coverage of up to 30 miles
(50 km).
■■ Mobile WiMAX  The details of the inner workings of Mobile WiMAX are
governed by the IEEE 802.16e standard. It was developed to support mobile
wireless clients—in other words, it was designed with the idea that users of
the network will not always be in a fixed location and may be in motion while
accessing the network.
Mobile WiMAX is purported to support wireless coverage of up to 10 miles
(15 km). Smart antenna technology, such as MIMO, is used in Mobile WiMAX
to improve gain and provide better throughputs.
Note  Mobile WiMAX and the Long Term Evolution (LTE) standard provide similar functionality
and are also technically similar. In fact, the two are considered competing standards, despite the
fact that WiMAX is used mostly for WMAN applications and LTE is used in WWAN applications.
Both are considered fourth-generation (4G) wireless network technologies.
WiMAX SIGs
Several WiMAX special interest groups exist, including the following:
■■ The WiMAX Forum  This group describes itself as an industry-led, non-
profit organization dedicated to certifying and promoting compatibility and
interoperability of products based on the IEEE 802.16 standard. The relationship
of the WiMAX Forum to WiMAX is similar to the relationship of the Wi-Fi
Alliance to WLAN technologies. The WiMAX Forum’s web site is at www
.wimaxforum.org/.
■■ Intel Corporation  Intel is a big proponent of WiMAX technology. This is
understandable because they are possibly the biggest manufacturer of the
hardware (chipsets) that implements WiMAX in the world. You can learn more
about Intel’s interest in WiMAX at www.intel.com/technology/wimax.
Wireless Personal Area Networks
A WPAN is used for facilitating communication between devices in a very small
area. The “personal” aspect of this wireless network type came about because the

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devices in question are often used in the context of a personal space. And as with other
communication types discussed thus far, WPAN’s objective is to receive and/or send data.
WPAN can be considered a short-range network because the range and reach of
this wireless network type is typically quite limited when compared with that offered
by WLANs, WMANs, and WWANs. A WPAN requires little external infrastructure to
operate; most WPANs are self-contained.
The IEEE 802.15 standards describe specifications for the inner workings of WPANs.
Several technologies exist for enabling WPANs, such as Bluetooth, ZigBee, Z-Wave,
Infrared Data Association (IrDA), and Ultra-Wideband (UWB), to mention a few. The
following sections discuss Bluetooth and ZigBee.
Bluetooth Overview
Bluetooth technology replaces the cables traditionally used for connecting numerous
electronic devices.
Bluetooth uses the frequency-hopping spread spectrum (FHSS) modulation technique.
Its devices operate in the 2.4–2.4835 GHz unlicensed frequency range.
Bluetooth Standards
The IEEE 802.15.1-2002 and IEEE 802.15.1-2005 standards are good examples of the
few Bluetooth standards that emerged from a neutral standards body. Most of the past
and future work done regarding the development of Bluetooth is accomplished by the
Bluetooth SIG.
Bluetooth Components and Architecture
Bluetooth devices consist primarily of the same components that make up most wireless
RF devices: transmitter and receiver components (the transceiver) and the baseband.
Protocols  The Bluetooth standard defines a group of protocols that are used to manage
communications between the devices. Most commonly used Bluetooth protocols are
listed in Table 7-1.
Profiles  Bluetooth devices make use of profiles to determine the services and protocols
that are supported by the device. This is a useful but somewhat confusing feature of
the technology. It is useful because it makes it easy for hardware manufacturers and
Bluetooth software developers to create Bluetooth devices and applications that are
very specific in scope. In other words, it helps to keep things simple and possibly bring
down the costs of Bluetooth devices because they do not need to support a plethora of
features.
The confusion can result on the user side because the unknowing user may assume
that all Bluetooth-capable devices can be used for any type of communication with
any other Bluetooth device. This is incorrect, however, because to communicate, two
Bluetooth devices must be able to speak the same profile.
Some common Bluetooth profiles are listed in Table 7-2.

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Bluetooth Protocol
Description
Object Exchange (OBEX)
A simple file transfer protocol that defines data objects.
Bluetooth devices use this communication protocol to
exchange those objects.
Bluetooth Network
Encapsulation Protocol
(BNEP)
Used for transporting and encapsulating Ethernet
packets. It can therefore be used for transporting
IPv4 and IPv6 protocols since they can in turn be
encapsulated within Ethernet packets.
RFCOMM
Used for emulating serial type connections by
emulating the serial cable line settings and the status
of an RS-232 serial port.
Link Manager Protocol (LMP) Used for setting up and controlling the logical
transports, logical links, and physical links. Controls
the communication links between devices.
Logical Link Control and
Adaptation Protocol (L2CAP)
Bluetooth protocols that operate at the higher layers
rely on L2CAP to provide an interface (logical channel)
for communicating with the rest of the Bluetooth
protocol stack.
Service Discovery Protocol
(SDP)
Used to discover (by searching or browsing) and learn
about the characteristics of the services offered by
other Bluetooth devices.
Telephony Control Protocol Manages call control for voice and data calls between
(TCP)
Bluetooth devices.
Audio/Video Control
Used for transporting the messages used for
Transport Protocol (AVCTP) controlling Audio/Video (A/V) devices.
Audio/Video Distribution Defines procedures for negotiating, establishing, and
Transport Protocol (AVDTP) transmitting Audio/Video (A/V) streams.
Table 7-1.  Bluetooth Protocols
Network  Two or more Bluetooth devices communicate with one another using a
piconet, a type of Bluetooth network that comprises one master and one or more slaves.
The master is responsible for regulating all access to the Bluetooth RF channel. The
bandwidth of the RF channel is shared among the participating Bluetooth devices in
the piconet. Each piconet operates in its own frequency-hopping radio channel.
A piconet is exclusive, in that a maximum of only seven active slaves (and one
master) are allowed to participate in the network at a time. However, other slaves are

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Bluetooth Profile
Generic Object Profile (GOEP)
Dial-Up Network Profile (DUN)
File Transfer Profile (FTP)
PAN profile
Service Discovery Application
Profile (SDAP)
Human Interface Device
Profile (HID)
Description
Implements the OBEX protocol; used for file
exchange—to transfer objects (files) from one
Bluetooth device to another.
Used to access the Internet and other dial-
up services over Bluetooth—for example,
by connecting wirelessly over Bluetooth to
a mobile phone, which in turn provides the
connection to the Internet.
Used for browsing, manipulating, and
transferring objects on file systems. Provides
similar functionality to TCP/IP FTP.
The implementation of the BNEP.
Specifies how an application should use the
SDP to discover services on another device.
Used for connecting various Bluetooth-based
input devices—keyboards, mice, scanners,
joysticks, etc.
Table 7-2.  Common Bluetooth Profiles
allowed to wait outside the piconet until any of the seven slaves leaves the network.
These waiting slaves, in a parked state, can join the piconet after a vacancy has been
created. Up to 255 devices can exist in an inactive, or parked, state, and the master
device can bring these into active state at any time. Active member slaves are referred
to as being in an active state.
When two or more established piconets are in proximity of each other, they form a
scatternet, which forms as a result of the individual piconets having overlapping radio
frequency coverage areas. The slaves in one piconet can participate in another piconet
in the role of either a master or a slave.
Figure 7-2 shows some Bluetooth network topologies. It shows two separate
piconets (Piconet-A and Piconet-B), and it also shows how the two piconets can
combine to form a scatternet.
Bluetooth Incarnations
Bluetooth technology has grown and developed a lot over the years since its inception,
and, as a result, a few versions are out there (as of this writing): Bluetooth 1.2, 2.0, 2.1,
and 3.0.

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Piconet - A
Piconet - B
Scatternet
Master
Slave
Parked
Figure 7-2.  Bluetooth network topologies
Bluetooth SIGs and Manufacturers
A prominent Bluetooth SIG is the aptly named Bluetooth SIG (www.bluetooth.org), a
non-profit trade association. Among other things, the group is tasked with publishing
Bluetooth specifications, qualifying Bluetooth devices, and promoting the Bluetooth
trademark.
Several big-name Bluetooth hardware and software vendors abound and include
Ericsson, Intel, Toshiba, Lenovo, Microsoft, Motorola, and Nokia, to name a few.
ZigBee Overview
ZigBee is especially suited for use in embedded applications that require low data rates
and low power consumption. ZigBee is targeted for use in wireless monitoring and
control systems and automation type applications. Its low cost, low power, and open
standards–based attributes are some of its key differentiating points.

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ZigBee uses the direct-sequence spread spectrum (DSSS) modulation technique.
It operates in different frequency bands in various parts of the world. For example,
in Europe, it works in the 868–868.8 MHz range; in North America, it works in the
902–928 MHz range; and worldwide, it works in the 2400–2483.5 MHz range.
ZigBee is based on the specifications described in the IEEE 802.15.4 standards.
ZigBee Components and Architecture
From a wireless network administrator’s point of view, the components of a ZigBee
network are relatively few and simple.
The players in a ZigBee network can be grouped broadly into two components: the
physical components and the logical components. We start with the logical components
in Table 7-3. The physical components are shown in Table 7-4.
ZigBee WPANs use a mesh network type of architecture, which is described as a
“self-healing” network. This basically means that nodes (ZigBee devices) are pretty
smart and knowledgeable about their surroundings and know how to work around
faults and other simple kinks in the communication links between its members. ZigBee
networks can support up to 64,000 nodes.
A sample wireless network made up of ZigBee devices is shown in Figure 7-3.
ZigBee Incarnations
As of this writing, few incarnations of the ZigBee suite exist, but two notable ones are the
■■ ZigBee, the original standard, and
■■ ZigBee Pro, with optimizations to accommodate more nodes in a ZigBee network.
ZigBee Special Features
ZigBee hardware generally cost less than other competing technologies that perform
similar functions, such as Bluetooth. Despite the lower cost, devices using ZigBee have not
yet achieved the market penetration and acceptance of the more expensive competition.
Logical Roles
ZigBee coordinator
ZigBee router
ZigBee end device
Characteristics
Initializes a network
Manages other network nodes
Stores network node information
Routes messages between paired nodes
Acts as a leaf node in the network
Table 7-3.  Logical Components of a ZigBee Network

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Physical Component Possible Logical Role Characteristics
Reduced Function ZigBee end device
Device (RFD)
Used mostly for sending or receiving
data; searches for available network;
requests data from the network
coordinator
Cannot become a ZigBee coordinator
Does not communicate directly with
other RFDs
Minimum hardware resources
(e.g. memory)
Full Function
Device (FFD)
Often battery powered
ZigBee end device Can function as a coordinator, as a
ZigBee coordinator router, or as another RFD
ZigBee router
Can be battery powered or powered
directly from the mains
Table 7-4.  Physical Components of a ZigBee Network
Figure 7-3.  A sample ZigBee network
ZigBee coordinator
ZigBee router
ZigBee router

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ZigBee SIGs and Manufacturers
A prominent ZigBee SIG is the ZigBee Alliance, “an association of companies working
together to enable reliable, cost-effective, low-power, wirelessly networked, monitoring
and control products based on an open global standard,” according to its web site
at www.zigbee.org. Sample manufacturers that make ZigBee-based devices include
Emerson, Freescale, Ember, and Philips.
Summary
Wireless Wide Area Networks (WWANs) include some specific WWAN implementations—
specifically, GSM, GPRS, UMTS, and LTE.
Wireless Metropolitan Area Networks (WMANs) include WiMAX networks.
Wireless Personal Area Networks (WPANs) use Bluetooth and ZigBee
implementations.

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Part IV
Protocols, Services,
and Security in Wireless
Networks

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and Protocols: TCP/IP
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Key Skills and Concepts
■■ Learn about the Transmission Control Protocol (TCP).
■■ Learn about the User Datagram Protocol (UDP).
■■ Learn about the Internet Protocol (IP) and IP versions 4 and 6.
■■ Understand how hosts are addressed on IP networks.
At this point, you should know about various aspects of wireless networks,
including the standards governing the operations of wireless networks and
the various client-side and infrastructure-side hardware that implement the
specifications described in the standards.
In this part of the book, we’ll shift our focus slightly and consider some real-
world aspects of managing a wireless network. Specifically, you’ll learn about some
of the protocols and services that work invisibly in the background to make wireless
networks useful to the end user.
These services and protocols are essential to the proper functioning of the wireless
network. They are also normally transparent to the end user—at least until one of the
services becomes unavailable.
Even though the main aspects of the wireless network (Physical layer and Media
Access Control sublayer) may be configured and working properly, incorrectly configured
or nonfunctioning upper-layer components can make a wireless network unusable.
For example, the Transmission Control Protocol and Internet Protocol (TCP/IP) suite
discussed next is used extensively by the nodes in a wireless network for addressing each
other, locating each other, locating other network resources, transferring packets back, and
so on.
TCP/IP and UDP
Transmission Control Protocol and Internet Protocol (TCP/IP) refers to an entire suite
of protocols used for network communications. Even though the TCP/IP suite consists
of several other protocols, the entire suite gets its name from two very important
protocols in the suite—TCP and IP.
TCP and IP are both upper layer protocols in the OSI conceptual model. Specifically,
IP operates at layer 3 and TCP operates at layer 4. The two protocols complement one
another and often work hand-in-hand. For this reason, they are often regarded as a
single entity. The following sections, however, cover IP (version 4) and TCP individually.
Internet Protocol
IP operates at layer 3, the Network layer, of the OSI model. IP communicates directly
with connected nodes in a network and connects with nodes that are not directly
connected (such as nodes on other subnets, the Internet, and so on). This means that an
IP packet can make its way to any other host, so long as a path exists to the destination.

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Headers
Network protocols use a header to describe the information needed to move data
from one host to the next. Packet headers, as they are typically called, consist of
information that tells the protocol how to handle the packet.
Packet headers tend to be small in size; this leaves room in the packet for the
actual (useful) data payload.
As each layer processes the packet, appropriate headers are removed. For
example, in the case of a TCP/IP packet over a IEEE 802.11 wireless network, the
driver will strip off the 802.11 Media Access Control (MAC) headers, IP will strip
the IP headers, and TCP will strip the TCP headers. This will eventually leave just
the data that needs to be delivered to the appropriate application.
IP helps move a packet from one host to another. Once a packet arrives at the host,
no information appears in the IP header to indicate to which application the data
should be delivered. IP does not provide any more features than those of a simple
transport protocol because it was meant to be a foundation for other protocols. Of
the protocols that use IP, not all of them need reliability, and the order of arrival of
the packets is not important. Thus, it is the responsibility of higher level protocols to
provide features beyond what IP provides.
IP Version 4
IPv4, as of the time of this writing, is the most prevalent version of IP in use around
the world. Figure 8-1 shows the components of the header of an IP packet. We’ll walk
through a description of each of the fields of an IP packet header.
4-bit IP
Version
4-bit Header 8-bit Differentiated
Length
Services (DiffServ)
16-bit Identification
16-bit Total Length (in bytes)
3-bit
Flags
13-bit Fragment Offset
8-bit Time to Live (TTL)
8-bit Protocol
16-bit Header Checksum
32-bit Source IP Address
32-bit Destination IP Address
Options (if any)
Data (if any)
Figure 8-1.  IP header

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Version Field  The first value in the IP header is the version number and it shows the
version of IP in use.
Length Field  The next value is the length of the IP header. The value is important to know,
because optional parameters may be appended to the end of the base header. The header
length tells us how many, if any, options are included. To get the byte count of the total IP
header length, multiply the length number by 4. Typical IP headers will have the header
length value set to 5, indicating that 20 bytes of data are included in the complete header.
Differentiated Services (DiffServ) Field  DiffServ is used for classifying, managing, and
providing quality of service guarantees to network packets. It basically instructs IP
stacks as to the kind of treatment to be given to a packet. (See RFC 2474, www.faqs.org/
rfcs/rfc2474.html, for more details.) The use of DiffServ bits is sometimes referred to as
“packet coloring,” and the bits are used by networking devices for the purpose of rate
shaping and prioritization.
Total Length Field  This value tells you the total length of the complete packet, including
the IP and TCP headers, but not including the Ethernet headers. This value is represented
in bytes. An IP packet cannot be longer than 65,535 bytes.
Identification Number Field  This field is supposed to be a unique number used by a host
to identify a particular packet.
Flags Field  The flags in the IP packet tell you whether the packet is fragmented.
Fragmentation occurs when an IP packet is larger than the smallest maximum
transmission unit (MTU) between two hosts. MTU defines the largest packet that can be
sent over a particular network. For example, Ethernet’s MTU is 1500 bytes. Thus, if we
have a 4000-byte (3980-byte data + 20-byte IP header) IP packet that needs to be sent
over Ethernet, the packet will be fragmented into three smaller packets. The first packet
might be 1500 bytes (1480-byte data + 20-byte IP header), the second packet might also
be 1500 bytes (1480-byte data + 20-byte IP header), and the last packet will be 1040 bytes
(1020-byte data + 20-byte IP header).
Fragmentation Offset Field  The fragment offset value indicates which part of the
complete packet you are receiving. Continuing with the 4000-byte IP packet example,
the first fragment will include bytes 0–1479 of data and will have an offset value of 0.
The second fragment will include bytes 1480–2959 of data and will have an offset value
of 185 (or 1480/8). And the third and final fragment will include fragments 2960–3999
of data and will have an offset value of 370 (or 2960/8). The receiving IP stack will
reassemble these three packets into one large packet before passing it up the stack.
TTL Field  The time-to-live (TTL) field is a number between 0 and 255 that signifies
how much time a packet is allowed to have on the network before being dropped. The
idea behind this is that, in the event of a routing error where the packet is stuck in a
“routing loop,” the TTL would cause the packet to time out and be dropped eventually,
thus keeping the network from becoming completely congested with looping packets.

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ICMP
ICMP was designed as a means for networked hosts to communicate with
one another about the state of the network. Since the data is used only by the
underlying operating system and not by users, ICMP does not support the notion
of port numbers, it does not require reliable delivery, and it doesn’t guarantee the
order of packets.
Every ICMP packet contains a type field that tells the recipient the nature of the
message. The most popular type is Echo-Request, which is used by the infamous
ping program. When a host receives the ICMP Echo-Request message, it responds
with an ICMP Echo-Reply message. This allows the sender to confirm that the
other host is up, and since we can see how long it takes the message to be sent and
replied to, we get an idea of the latency of the network between the two hosts.
As each router processes the packet, the TTL value is decreased by 1. When the TTL
reaches 0, the router on which this happens sends a message via Internet Control
Message Protocol (ICMP), informing the sender of this (see the “ICMP” sidebar).
Protocol Field  This field tells you to which higher level protocol this packet should be
delivered. Typically, this has a value for TCP, UDP, or ICMP.
Header Checksum  The last small value in this IP header is the checksum. This field
holds the sum of every byte in the IP header, including any options. When a host builds
an IP packet to send, it computes the IP checksum and places it into this field. The
receiver can then do the same math and compare values. If the values don’t match, the
receiver knows that the packet was corrupted during transmission. (For example, a
lightning strike creating an electrical disturbance might create packet corruption.)
Source and Destination IP Address Fields  Finally, the numbers that matter the most in an
IP header are the source and destination IP addresses. These values are stored as 32-bit
integers instead of the more human-readable dotted-decimal notation. For example,
instead of 192.168.1.1, the value would be hexadecimal c0a80101 or decimal 3232235777.
Transmission Control Protocol
TCP operates at the transport layer (layer 4) of the OSI model. TCP provides a reliable
transport for one communication session—that is, a single connection from a client
program to a server program.
In addition to sessions, TCP also handles the ordering and retransmission of
packets. If a series of packets arrive out of order, the stack will put them back into
order before passing them up to the application. If a packet arrives with any kind
of problem or goes missing altogether, TCP will automatically request the sender to
retransmit. Finally, TCP connections are also bidirectional. This means that the client
and server can send and receive data on the same connection.

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16-bit Source Port Number
16-bit Destination Port Number
32-bit Sequence Number
32-bit Acknowledgment Number
4-bit Header 6-bit
Length
Reserved
UAP R S F
RCS SY I
GKH T NN
16-bit Window Size
16-bit TCP Checksum
16-bit Urgent Pointer
Options (if any)
Data (if any)
Figure 8-2.  TCP header
The TCP header is similar to the IP header in that it packs quite a bit of information
into a little bit of space. You can use Figure 8-2 as a reference as you read about the
various fields of a TCP packet header.
Source and Destination Port Fields  Ports are numerical identifiers used in TCP/IP-based
network communications for allowing multiple process-to-process communications
to occur simultaneously within a host. Port numbers are therefore used to identify
processes or services running within a host. In TCP/IP, port numbers are integers
between 0 and 65,535.
The first two pieces of information in a TCP header are the source and destination
port numbers. Because these are only 16-bit values, their range is 0 to 65535. Typically,
the source port is a value greater than 1024, since ports 1–1023 are reserved for system
use on most operating systems (including Linux, Solaris, and the many variants of MS
Windows). On the other hand, the destination port is typically low; most of the popular
services reside there, although this is not a requirement.
Sequence and Acknowledgment Fields  The next two numbers in the TCP header are the
sequence and acknowledgment numbers. These values are used by TCP to ensure that the
order of packets is correct and to let the sender know which packets have been properly
received. In day-to-day administrative tasks, you shouldn’t have to deal with them.
Whenever the packet has the acknowledgment flag set, it can be used by the receiver
to confirm how much data has been received from the sender (see “Miscellaneous Flags
Field”).
Header Length  Similar to IP’s header length, TCP’s header length tells us the header’s
length, including any TCP options. Whatever value appears in this field is multiplied
by 4 to get the byte value.

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Miscellaneous Flags Field  This field is a bit tricky. TCP uses a series of flags to indicate
whether the packet is supposed to initiate a connection, contain data, or terminate a
connection. The flags (in the order in which they appear) are Urgent (URG), Acknowledge
(ACK), Push (PSH), Reset (RST), Synchronize (SYN), and Finish (FIN). Their meanings are
as follows:
■■ URG  Implies that urgent data is in the packet and should receive priority
processing.
■■ ACK  Acknowledgment of successfully received data.
■■ PSH  Request to process any received data immediately.
■■ RST  Immediately terminates the connection.
■■ SYN  Request to start a new connection.
These flags are typically used in combination with one another. For example, it is
common to see PSH and ACK together. Using this combination, the sender essentially
tells the receiver two things:
■■ Data in this packet needs to be processed.
■■ Acknowledges that the data packet was received successfully.
Window Size Field  This is the next field in a TCP header. TCP uses a technique called sliding
window, which allows each side of a connection to tell the other how much buffer space it
has available for dealing with connections. When a new packet arrives on a connection, the
available window size decreases by the size of the packet until the operating system has a
chance to move the data from TCP’s input buffer to the receiving application’s buffer space.
Window sizes are computed on a connection-by-connection basis.
TCP Checksum Field  The TCP checksum is similar to the IP checksum in that its
purpose is to give the receiver a way of verifying that the data received isn’t corrupted.
Unlike the IP checksum, the TCP checksum actually takes into account both the TCP
header as well as the data being sent.
Urgent Pointer Field  The last piece of the TCP header, the urgent pointer, points to the
offset of the octet following important data. This value is observed when the URG flag
is set and tells the receiving TCP stack that some important data is present. The TCP
stack is supposed to relay this information to the application so that it knows it should
treat that data with special importance.
In reality, you’ll be hard pressed to see a packet that uses the URG bit. Most
applications have no way of knowing whether data sent to them is urgent or not, and
most applications don’t really care.
TCP in Action
As alluded to earlier, TCP supports the concept of a connection. Each connection must
go through a sequence to get established; once both sides are done sending data, they
must go through another sequence to close the connection.

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The complete process of opening a TCP connection, sending data, and tearing down
the connection is reviewed here.
Note that the information provided here has been highly simplified, and,
unfortunately, because of the complex nature of TCP, it is impossible to cover every
possible scenario that a TCP connection can take. However, this information should
be enough to help you determine when things are going wrong at the network level.
Opening a Connection  TCP goes through a three-way handshake for every connection that
it opens to allow both sides to send each other their state information and give each
other a chance to acknowledge the receipt of that data.
1. The first packet is sent by the host that wants to open the connection with a
server. Let’s call this host the client. The client sends a TCP packet over IP and
sets the TCP flag to SYN. The sequence number is the initial sequence number
that the client will use for all the data it will send to the other host (the server).
2. The second packet is sent from the server to the client. This packet has two TCP
flags set: SYN and ACK. The ACK tells the client that it has received the first
(SYN) packet. This is double-checked by placing the client’s sequence number
in the acknowledgment field. The SYN tells the client with which sequence
number the server will be sending its responses.
3. The third packet goes from the client to the server. It has only the ACK bit set
in the TCP flags for the purpose of acknowledging to the server that it received
its SYN. This ACK packet has the client’s sequence number in the sequence
number field and the server’s sequence number in the acknowledgment field.
This should be enough to establish a connection.
So why all the hassle to start a connection? Why can’t the client just send a single
packet over to the server stating, “I want to start talking—okay?” and have the server
send back an “okay”? The reason is that without all three packets going back and forth,
neither side is sure that the other side received the first SYN packet—and that packet is
crucial to TCP’s ability to provide a reliable and correctly ordered transport.
Transferring Data  With a fully established connection in place, both sides are able to
send data. The data is automatically processed and made available to the actual upper
layer applications that need it.
The process of the server sending some data and then getting an acknowledgment
from the client can continue as long as data needs to be sent.
Closing the Connection  TCP connections have the option of ending ungracefully. That is
to say, one side can tell the other “stop now!” Ungraceful shutdowns are accomplished
with the RST (reset) flag, which the receiver does not acknowledge upon receipt. This
is to keep both hosts from getting into a “RST war,” where one side resets and the other
side responds with a reset, thus causing a never-ending ping-pong effect.
As the first step of shutting down a connection, the side that is ready to close the
connection sends a packet with the FIN bit set, indicating that it is finished. Once a host

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has sent a FIN packet for a particular connection, it is not allowed to send anything
other than acknowledgments. This also means that even though it may be finished, the
other side may still send it data. It is not until both sides send a FIN that both sides are
finished. And like the SYN packet, the FIN packet must receive an acknowledgment.
And that’s all there is to a graceful connection shutdown.
User Datagram Protocol
Like TCP, UDP is a popular transport layer protocol. Unlike TCP, however, it does not
provide reliability. In other words, UDP won’t detect lost or duplicate packets the way
TCP does. UDP does, however, have its own strengths. It is a good choice for two types
of traffic: short request/response transactions that fit in one packet (such as DNS) and
streams of data that are better off skipping lost data and moving on (such as streaming
audio and video). In the first case, UDP is better because a short request/response
usually doesn’t merit the overhead that TCP requires to guarantee reliability. The
application is usually better off adding additional logic to retransmit on its own in the
event of lost packets.
For example, when dealing with streaming data, TCP’s reliability mechanisms
may have undesirable effects, because it may be preferable for some lost packets to
be simply skipped instead of being retransmitted. This is because human listeners/
viewers are much better at handling (and much less annoyed by) short drops in audio
than they are in delays.
In comparison to the header of a TCP packet, a UDP packet header is much simpler.
Figure 8-3 shows a sample UDP header.
■■ Source and Destination ports  The first fields in the UDP header are
conceptually the same as the TCP port numbers.
■■ Length Field  The length of the packet is specified; the field is16-bits long and
specifies the length in bytes of the entire datagram, which consists of both the
packet header and the actual data payload.
■■ UDP checksum  This field is used by UDP to validate that the data has
arrived to its destination without corruption.
16-bit Source Port Number
16-bit Destination Port Number
16-bit UDP Length
16-bit UDP Checksum
Data (if any)
Figure 8-3.  UDP packet header

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IP-Based Networks
Now that you have some of the fundamentals of TCP/IP under your belt, let’s take a
look at how it helps us glue networks together. This section covers hosts and networks,
netmasks, static routing, and some basics in dynamic routing.
Hosts and Networks
The Internet is, of course, a large group of interconnected networks; each of these
component networks has agreed to connect with some other network, and each is
assigned a network address.
Traditionally, in a 32-bit IP address, the network component typically takes up 8,
16, or 24 bits to encode a class A, B, or C network, respectively. Since the remainder of
the bits in the IP address are used to enumerate the host within the network, the fewer
bits that are used to describe the network, the more bits are available to enumerate the
hosts. For example, class A networks have 24 bits left for the host component, which
means there can be upward of 16,777,214 hosts within that network. (Classes B and C
have 65,534 and 254 nodes, respectively.)
Note  Class D and class E ranges also exist. Class D is used for multicast, and class E is
reserved for experimental use.
To organize the various classes of networks, it was decided early in IP’s life that
the first few bits would determine to which class the address belonged. For the sake of
readability, the first octet of the IP address specifies the class.
Note  An octet is 8 bits, which in the typical dotted-decimal notation of IP means the number
before a dot. For example, in the IP address 192.168.1.42, the first octet is 192, the second octet is
168, and so on.
The class ranges are shown in Table 8-1.
Some special addresses are reserved for special uses. The first special address is one
you are likely to be familiar with: 127.0.0.1. This is also known as the loopback address.
It is set up on every host using IP so that it can refer to itself. It seems a bit odd to do it
Class
A
B
C
First Octet Range
0–127
128–191
192–223
Table 8-1.  IPv4 Address Classification
Examples
1.1.1.1 and 10.0.7.9
128.9.8.10 and 168.0.0.78
192.169.0.9 and 223.1.2.25

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this way, but just because a system is capable of speaking IP doesn’t mean it has an IP
address allocated to it! On the other hand, the 127.0.0.1 address is virtually guaranteed.
(If it isn’t there, you know that something has probably gone wrong.)
Three other ranges are notable: Every IP in the 10.0.0.0 network, the 172.16–172.31
networks, and the 192.168 network is considered a private IP. These ranges are not
allowed to be allocated to anyone on the Internet, and, therefore, you may use them on
your internal networks.
Note  Internal networks are networks that are behind a sort of firewall—not really directly
exposed to the Internet—or that are connected to the Internet through some sort of device that is
itself connected to the public Internet. Many wireless access points (WAPs) or wireless residential
gateways are able to act as such a device.
Subnetting
Imagine a wireless network with a few thousand hosts on it, which is not unreasonable
in a medium-sized company. Trying to tie them all together into a single large network
would probably make you pull your hair out, bang your head on the wall, or possibly
both. And that’s just the figurative stuff.
The reasons for not keeping a network as a single large entity range from technical
issues to political ones. On the technical front, there are limitations to every technology
on how large a network can get before it becomes too large. Ethernet, for instance, cannot
have more than 1024 hosts on a single collision domain. Realistically, having more than
a dozen on an even mildly busy network will cause serious performance issues. Even
migrating hosts to switches doesn’t solve the entire problem, since switches, too, have
limitations on how many hosts they can deal with.
Of course, you’re likely to run into management issues before you hit limitations of
switches; managing a single large network is difficult. Furthermore, as an organization
grows, individual departments will begin compartmentalizing. Human Resources is
usually the first candidate to need a secure network of its own so that nosy engineers
don’t peek into things they shouldn’t. To support a need like that, you need to create
subnetworks, a task more commonly referred to as subnetting.
Assuming our corporate network is 10.0.0.0, we could subnet it by setting up
smaller class C networks within it, such as 10.1.1.0, 10.1.2.0, 10.1.3.0, and so on. These
smaller networks would have 24-bit network components and 8-bit host components.
Since the first 8 bits would be used to identify our corporate network, we could use
the remaining 16 bits of the network component to specify the subnet, giving us 65,534
possible subnetworks. Of course, you don’t have to use all of them!
Netmasks
The purpose of a netmask, often called a subnet mask, is to tell the IP stack which part of
the IP address is the network and which part is the host. The netmask allows the stack
to determine whether a destination IP address is on the LAN or if it needs to be sent to
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The best way to start looking at netmasks is to look at IP addresses and netmasks in
their binary representations. Let’s look at the 192.168.1.42 address with the netmask of
255.255.255.0:
Dotted Decimal
192.168.1.42
255.255.255.0
Binary
11000000 10101000 00000001 00101010
11111111 11111111 11111111 00000000
In this example, we want to find out what part of the IP address 192.168.1.42 is
network and what part is host. Now, according to the definition of netmask, those 0 bits
are part of the host. Given this definition, we see that the first three octets make up the
network address and the last octet makes up the host.
In discussing network addresses with other people, you’ll find it handy to be able
to state the network address without explicitly providing the original IP address and
netmask. Thankfully, this network address is computable, given the IP address and
netmask, using a bitwise AND operation.
The way the bitwise AND operation works can be best explained by observing
the behavior of two bits being ANDed together. If both bits are 1, then the result of
the AND is also 1. If either bit (or both bits) is 0, the result is 0. You can see this more
clearly in Table 8-2.
So computing the bitwise AND operation on 192.168.1.42 and 255.255.255.0 yields
the bit pattern 11000000 10101000 00000001 00000000. Notice that the first three octets
remained identical and the last octet became all zeros. In dotted-decimal notation, this
reads 192.168.1.0.
Note  We need to give up one IP to the network address and one IP to the broadcast address. In
this example, the network address is 192.168.1.0, and the broadcast address is 192.168.1.255.
Let’s walk through another example. This time, we want to find the address range
available to us for the network address 192.168.1.176 with a netmask of 255.255.255.240.
(This type of netmask is commonly given by Internet service providers [ISPs] to
business digital subscriber line [DSL] and T1 customers.)
Bit 1
Bit 2
0
0
0
1
1
0
1
1
Table 8-2.  ANDing Bits
Result of Bitwise AND
0
0
0
1

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A quick breakdown of the last octet in the netmask shows us that the bit pattern for
240 is 11110000. This means that the first three octets of the network address plus 4 bits into
the fourth octet are held constant (255.255.255.240 in binary is 11111111 11111111 11111111
11110000). Since the last 4 bits are variable, we know we have 16 possible addresses (24 = 16).
Thus, our range goes from 192.168.1.176 to 192.168.1.192 (192 − 176 = 16).
Because it is so tedious to type out complete netmasks, most people use the
abbreviated format, in which the network address is followed by a slash and the
number of bits in the netmask. So the network address 192.168.1.0 with a netmask
of 255.255.255.0 would be abbreviated as 192.168.1.0/24.
IPv6
IPv6 is the moniker for version 6 of the Internet Protocol. It is also referred to as
IPng—Internet Protocol, the Next Generation. IPv6 offers many new features and
improvements over its predecessor IPv4, including the following:
■■ A larger address space
■■ Built-in security capabilities, with network-layer encryption and authentication
■■ A simplified header structure
■■ Improved routing capabilities
■■ Built-in auto-configuration capabilities
IPv6 Address Format
IPv6 is able to offer an increased address space because it is 128-bits long (compared to
the 32 bits for IPv4). Because an IPv6 address is 128-bits long (or 16 bytes), about 3.4 ×
10^38 possible addresses are available (compared to the roughly 4 billion available
for IPv4).
A human being able to represent or memorize (without error) a string of digits that
is 128-bits long on paper is no easy feat. Therefore, several abbreviation techniques
are used to make it easier to represent or shorten an IPv6 address to make it more
human-friendly. The 128 bits of an IPv6 address can be shortened by representing the
digits in hexadecimal format. This effectively reduces the total length to 32 digits in
hexadecimal. IPv6 addresses are written in groups of four hexadecimal numbers. The
eight groups are separated by colons (:). Here’s a sample IPv6 address:
0012:0001:0000:0000:2345:0000:0000:6789
The leading zeros of a section of an IPv6 address can be omitted—for example, the
sample address can be shortened to this:
12:1:0000:0000:2345:0000:0000:6789

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The rule also permits the preceding address to be rewritten like this:
12:1:0:0:2345:0:0:6789
One or more consecutive four-digit groups of zeros in an IPv6 address can be
shortened and represented by double colon symbols (::), as long as this is done only
once in the entire address. Therefore, using this rule, our sample address can be
abbreviated like so:
12:1::2345:0:0:6789
Using the proviso in the preceding rule would make the following address invalid,
because more than one set of double colons is in use:
12:1::2345::6789
IPv6 Address Types
Several types of IPv6 addresses can be used, and each address type has additional
special address types, or scopes, that are used for different purposes. Three particularly
special IPv6 address classifications are unicast, anycast, and multicast addresses. These
are discussed next.
Unicast Addresses
A unicast address in IPv6 refers to a single network interface. Any packet sent to
a unicast address is meant for a specific interface on a host. Examples of unicast
addresses are link-local (for example, ::/128 - unspecified address, ::1/128 - loopback
address, fe80::/10 - autoconfiguration addresses), global unicast, site-local, and other
special addresses.
Anycast Addresses
An anycast address is assigned to multiple interfaces (possibly belonging to different
hosts). Any packet sent to an anycast address will be delivered to the closest interface
that shares the anycast type address—“closest” is interpreted according to the routing
protocol’s idea of distance, or it’s simply the most easily accessible host. Hosts in a
group sharing an anycast address have the same address prefix.
Multicast Addresses
An IPv6 multicast-type address is similar in functionality to an IPv4-type multicast
address. A packet sent to a multicast address will be delivered to all the hosts (interfaces)
that have the multicast address. The hosts (or interfaces) that make up a multicast group
do not necessarily need to share the same prefix and also do not need to be connected to
the same physical network.

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IPv6 Backward-Compatibility
The designers of IPv6 built in backward-compatibility functionality into the version to
accommodate the various hosts or sites that are not fully IPv6-compliant or ready. The
support for legacy IPv4 hosts and sites is handled in several ways: compatible addresses
(IPv4-compatible IPv6 address), mapped address (IPv4-mapped IPv6 address), and
tunneling.
Mapped Addresses  Mapped addresses are special unicast-type addresses used by IPv6
hosts. They are used when an IPv6 host needs to send packets to an IPv4 host via a
mostly IPv6 infrastructure. The format for a mapped IPv6 address is as follows: the first
80 bits are all 0’s, followed by 16 bits of 1’s, and ending with 32 bits of the IPv4 address.
Compatible Addresses  The compatible type of IPv6 address is used to support IPv4-
only hosts or infrastructures—that is, those that do not support IPv6 in any way. It can
be used when an IPv6 host wants to communicate with another IPv6 host via an IPv4
infrastructure. The first 96 bits of a compatible IPv6 address is made up of all 0’s and
ends with 32 bits of the IPv4 address.
Tunneling  This method is used by IPv6 hosts that need to transmit information over a
legacy IPv4 infrastructure using configured tunnels. This is achieved by encapsulating
an IPv6 packet in a traditional IPv4 packet and sending it via the IPv4 network.
Summary
The TCP/IP protocol is a very important part of today’s wireless and wired networks
and this is why an entire chapter has been devoted to it. This chapter covered the
fundamentals of TCP/IP, including IP, TCP, UDP, IP addressing, subnetting, netmasks,
and IP versions 4 and 6. We also examined the fields of some of the headers of the
protocols that we discussed.

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Standard Wireless Network
Infrastructure Services and
Protocols: DNS, DHCP
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Wireless Network Administration: A Beginner’s Guide
Key Skills and Concepts
■■ Learn about key infrastructure services that support wireless networks.
■■ Understand the Domain Name System (DNS).
■■ Understand the Dynamic Host Configuration Protocol (DHCP).
Chapter 8 laid the foundation for this chapter’s discussion of the standard services
that exist higher up in the Open System Interconnection (OSI) conceptual model.
Specifically, these protocols are implemented above the Network and Transport
layers, and they rely heavily on the functionality provided by the lower layer protocols.
In other words, the protocols discussed in this chapter are encapsulated by the lower
layer protocols.
This chapter provides a cursory description of the protocols but does not go into any
configuration details of the protocols themselves. The wireless network administrator
is often responsible for managing and configuring these back-end services and needs
to understand the roles and interrelationships of these services in the overall network
infrastructure.
Domain Name System
The Domain Name System (DNS) provides a means of mapping numerical IP addresses
(discussed in Chapter 8) into people-friendly and easy-to-remember names. This
translation isn’t mandatory, but it does make the network much more useful and easier
to work with for humans.
This section offers some background material that will help you understand the
inner workings of DNS.
Domain and Host Naming Conventions
Until now, you’ve most likely referenced sites by their fully qualified domain name
(FQDN), like this one: www.ieee802.org. Each string of characters between the dots in
this FQDN is significant.
Starting from the right end and moving to the left, we have the top-level domain
component, the second-level domain component, and the third-level domain component.
Third-level domain
serverA .
example .
Top-level domain
org .
Second-level domain
Root domain
Figure 9-1.  FQDN for serverA.example.org

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This is illustrated in Figure 9-1 in the FQDN for a system (serverA.example.org) and is a
classic example of a FQDN. Its breakdown is discussed in detail in the following section.
The Root Domain
The DNS structure is similar to that of an inverted tree—the root of the tree is at the top
and its leaves and branches are at the bottom (see Figure 9-2).
At the top of the inverted domain tree is the highest level of the DNS structure,
aptly called the root domain and represented by the simple dot (.).
This is the dot that’s supposed to occur after every FQDN, but it is silently assumed
to be present even though it is not explicitly written. Thus, for example, the proper
FQDN for www. ieee802.org is really www.ieee802.org. (notice the root period/dot at
the end). And the FQDN for the popular web portal for Yahoo! is actually www.yahoo
.com. (likewise).
Coincidentally (or not), this portion of the domain name space is managed by a
bunch of special servers known as the root name servers. At the time of this writing,
a total of 13 root name servers were being managed by 13 providers. (And each
provider may have multiple servers distributed across the globe for various reasons,
such as security and load balancing.) Also at the time of this writing, 9 of the 13 root
name servers fully support IPv6 type record sets. The root name servers are named
alphabetically, with names like a.root-server.net, b.root-server.net, … m.root-server.net.
The role of the root name servers will be discussed in a bit.
The Top-Level Domain Names
The top-level domains (TLDs) can be regarded as the first branches that we would meet on
the way down from the top of our inverted tree structure. You could say that the top-level
domains provide the categorical organization of the DNS namespace. What this means
in plain English is that the various branches of domain namespace have been divided
into clear categories to fit different uses (examples of such uses could be geographical,
functional, and so on). At the time of this writing, more than 281 TLDs existed.
Root o.f DNS
Top-level
domains:
com
org
net edu
int mil gov Country codes
Individual
sites:
redhat
slashdot hyperreal ucr
caldera
planetoid
sjsu nato
lanl lbl
army af
navy
Figure 9-2.  The DNS tree, two layers deep

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These TLDs can be broken down further into the generic TLDs (such as .org,
.com, .net, .mil, .gov, .edu, .int, .biz), country-code TLDs (such as .us, .uk, .ng, and .ca,
corresponding to the country codes for the United States, the United Kingdom, Nigeria,
and Canada), and other special TLDs (such as the .arpa domain).
The TLD in our sample FQDN (serverA.example.org.) is .org.
The Second-Level Domain Names
The names at this level of the DNS make up the actual organizational boundary of the
namespace. Companies, Internet service providers (ISPs), educational communities,
non-profit groups, and individuals typically acquire unique names within this level.
Here are a few examples: ieee802.org, labmanual.org, kernel.org, and caffenix.com.
The second-level domain in our sample FQDN (serverA.example.org.) is example.
The Third-Level Domain Names
At this level of the domain namespace, individuals and organizations that have been
assigned second-level domain names can pretty much decide what to do with the
third-level names. The convention, though, is to use the third-level names to reflect
host names or other functional uses. It is also common for organizations to begin the
subdomain definitions from here. An example of functional assignment of a third-level
domain name will be the “www” in the FQDN www.yahoo.com. The “www” here can
be the actual host name of the machine under the umbrella of the yahoo.com domain,
or it can be an alias to a real host name.
The third-level domain name in our sample FQDN (serverA.example.org.) is serverA.
Here it simply reflects the actual host name of our system.
By keeping DNS structured in this manner, the task of keeping track of all the hosts
connected to the Internet is delegated to each site taking care of its own information.
The central repository listing of all the primary name servers, which is called the
root server, is the only list of existing top-level domains. Obviously, a list of such a
critical nature is very important, and as such it is mirrored across multiple servers and
multiple geographic regions. For example, an earthquake in Japan may destroy the root
server for Asia, but all the other root servers around the world can take up the slack
until it comes back online. The only difference noticeable to users might be a slightly
higher latency in resolving domain names.
Subdomains
While browsing the World Wide Web, you’ve probably come across names such as
www.support.example.org. Such names might make you wonder which part of the whole
name constitutes the host name component and which part makes up the domain name
component.
Welcome to the wild and mysterious world of subdomains. A subdomain exhibits
all the properties of a domain, except that it has delegated a subsection of the domain
instead of all the hosts at a site. Using the example.org site, the subdomain for the
support and help desk department of Example, Inc., would be support.example.org.

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When the primary name server for the example.org domain receives a request for a
host name whose FQDN ends in support.example.org, the primary forwards the request
down to the primary name server for support.example.org. Only the primary name
server for support.example.org knows all the hosts existing beneath it—hosts such as a
system named www with the FQDN of www.support.example.org.
Figure 9-3 shows the relationship from the root domain to example.org and then to
support.example.org. The “www” is, of course, the host name.
To make this clearer, let’s follow the path of a DNS request:
1. A client wants to visit a web site called www.support.example.org.
2. The query starts with the top-level domain, org., and within org. is example.org.
3. Let’s say one of the authoritative DNS servers for the example.org domain is
named ns1.example.org.
4. Since the host ns1 is authoritative for the example.org domain, we have to
query it for all hosts (and subdomains) under it.
5. So we query it for information about the host we are interested in: www.support
.example.org.
6. Now ns1.example.org’s DNS configuration is such that for anything ending
with support.example.org, the server must contact another authoritative server
called dns2.example.org.
7. The request for www.support.example.org is then passed on to dns2.example.org,
which returns the IP address for www.support.example.org—say, 192.168.1.10.
. (root domain)
org (top-level domain)
example (organization’s second-level domain)
serverA (host) support (subdomain for support department of example.org)
other hosts www (hostname for system under support subdomain)
Figure 9-3.  Structure of subdomains

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Note  Whenever a site name appears to reflect the presence of subdomains, it doesn’t always
imply that a subdomain is in use. Some DNS implementations allow the use of periods in the
host name. Thus, from time to time, you will see periods used in host names. Whether or not a
subdomain exists is handled by the configuration of the DNS server for the site. For example, www
.bogus.example.org does not automatically imply that bogus.example.org is a subdomain. Rather, it
may also mean that www.bogus is the host name for a system in the example.org domain.
Zones
The concept of DNS zones is sometimes misunderstood, and to try to clarify things here:
a DNS zone is not the same thing as a DNS domain. The difference is subtle, but important.
Domains are designated along organizational boundaries. A single organization can
be separated into smaller administrative subdomains. Each subdomain gets its own
zone. All of the zones collectively form the entire domain.
For example, .example.org is a domain. Within it are the subdomains .engr.example
.org, .marketing.example.org, .sales.example.org, and .admin.example.org. Each of the
four subdomains has its own zone. And .example.org has some hosts within it that
do not fall under any of the subdomains; thus it has a zone of its own. As a result, the
example.org domain is actually composed of five zones in total.
In the simplest model, where a single domain has no subdomains, the definition of
zone and domain are the same in terms of information regarding hosts, configurations,
and so on.
The in-addr.arpa Domain
DNS allows resolution to work in both directions. Forward resolution converts names
into IP addresses, and reverse resolution converts IP addresses back into host names.
The process of reverse resolution relies on the in-addr.arpa domain, where arpa is an
acronym for Address Routing and Parameters Area.
As explained in the preceding section, domain names are resolved by looking at each
component from right to left, with the suffixing period indicating the root of the DNS tree.
Following this logic, IP addresses must have a top-level domain as well. This domain is
called the in-addr.arpa for IPv4 type addresses. In IPv6, the domain is called ip6.arpa.
Unlike FQDNs, IP addresses are resolved from left to right once they’re under the in-
addr.arpa domain. Each octet further narrows down the possible host names. Figure 9-4
shows a visual example of reverse resolution of the IP address 138.23.169.15.
Types of DNS Servers
DNS servers come in three flavors: primary, secondary, and caching. Another special
class of name servers consists of the so-called “root name servers.” Other DNS servers
require the service provided by the root name servers every once in a while.
Primary Servers
Primary name servers are considered authoritative for a particular domain. An authoritative
server is the server on which the domain’s configuration files reside. Updates to the

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in-addr
arpa
0
1
2
138
255
23
0
1
255
0
1
2
169
255
15
0
1
2
255
15.169.23.138.in-addr.arpa
Figure 9-4.  Reverse DNS resolution of 138.23.169.15
domain’s DNS tables occur on this server. A primary name server for a domain is simply
a DNS server that knows about all hosts and subdomains existing under its domain.
Secondary Servers
Secondary name servers work as backups and as load distributors for the primary
name servers. Primary servers know of the existence of secondaries and send them
periodic updates to the name tables. When a site queries a secondary name server, the
secondary responds with authority. However, because it’s possible for a secondary
to be queried before its primary can alert it to the latest changes, some people refer
to secondaries as “not quite authoritative.” Realistically speaking, you can generally

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Root Name Servers
The root name servers are the very first port of call for the topmost parts of the
domain namespace. These servers publish a file called the “root zone file” to other
DNS servers and clients on the Internet. The root zone file describes where the
authoritative servers for the DNS top-level domains (.com, .org, .ca, .ng, .hk, .uk,
and so on) are located.
A root name server is just an instance of a primary name server—it delegates
every request it gets to another name server. Most DNS server implementations can
be configured to act like a personal root server—nothing terribly special about it.
trust secondaries to have correct information. (Besides, unless you know which is
which, you cannot tell the difference between a query response from a primary and one
received from a secondary.)
Caching Servers
Caching servers contain no configuration files for any particular domain. Instead, when
a client host requests a caching server to resolve a name, that server will check its own
local cache first. If it cannot find a match, it will find the primary server and ask it.
This response is then cached. Most current DNS server implementations are capable of
caching.
Note  A DNS server can be configured to act with a specific level of authority for a particular
domain. For example, a server can be primary for example.org but be secondary for domain.com.
All DNS servers act as caching servers, even if they are also primary or secondary for any other
domains.
Practically speaking, caching servers work quite well because of the temporal
nature of DNS requests. Their effectiveness is based on the premise that, if you’ve
asked for the IP address to example.org in the past, you are likely to do so again in
the near future. Clients can tell the difference between a caching server and a primary
or secondary server, because when a caching server answers a request, it answers it
“nonauthoritatively.”
Note  The DNS server implementation in a majority of wireless infrastructure devices are often
running in caching-only DNS server mode. This means that they need to be configured with the
address of some other DNS server that is authoritative for the namespace in which the wireless
network participates. Infrastructures devices such as access points and wireless gateways therefore
forward name-resolution requests to some other regular DNS server on the network. See Figure 9-5
for an illustration of a sample wireless network with an AP configured as a caching DNS server.

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Wireless
DNS client
DNS
queries
&
responses
Access point
acting as
caching DNS
server
Forwarded
DNS requests
&
responses
Primary DNS server
Figure 9-5.  Access point acting as a caching DNS server
DNS Record Types
Name server database files store specific information that pertains to each zone that the
server hosts. These database files consist mostly of record types—therefore, you need to
understand the meaning and use of the common DNS record types: SOA, NS, A, PTR,
CNAME, MX, TXT, and RP.
Note  Our excursion into DNS record types assumes that the data is stored in plain-text
configuration files. This is the traditional format for storing DNS records on most UNIX and UNIX-
like platforms. It is possible for DNS records to be stored in other formats, such as SQL database
or proprietary formats. The idea is all the same, however, and the facts about plain-text files are the
same in other platforms. The bottom line is that, regardless of the format and platform on which the
records are stored, a DNS record is a DNS record and will probably always be a DNS record.
SOA: Start of Authority
The SOA record starts the description of a site’s DNS entries. The format of this entry is
as follows (line numbers are added to the list to aid readability):
1 domain.name. IN SOA ns.domain.name. hostmaster.domain.name. (
2 1999080801; serial number
3 10800; refresh rate in seconds (3 hours)
4 1800; retry in seconds (30 minutes)
5 1209600; expire in seconds (2 weeks)
6 604800; minimum in seconds (1 week)
7)

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Line 1  Line 1 contains some important details: domain.name. is of course to
be replaced with your domain name or the zone name. Notice that last period at
the end of domain.name. It’s supposed to be there—indeed, some DNS server
implementations are extremely picky about it. The ending period is necessary for the
server to differentiate relative host names from FQDNs; for example, consider the
difference between serverA and serverA.example.org.
IN tells the name server that this is an Internet record. There are other types of
records, but it’s been years since anyone has had a need for them. You can safely ignore
them.
SOA tells the name server this is the Start of Authority record.
The ns.domain.name. is the FQDN for the name server for this domain (that
would be the server where this file will finally reside). Again, watch out and don’t miss
that trailing period.
The hostmaster.domain.name. is the e-mail address for the domain
administrator. Notice the lack of an @ in this address. The @ symbol is replaced by a
period. Thus, the e-mail address referred to in this example is hostmaster@domain.
name. The trailing period is used here, too.
The remainder of the record starts after the opening parenthesis on line 1.
Line 2  Line 2 is the serial number. It is used to tell the name server when the file
has been updated. Watch out—forgetting to increment this number when you make
a change is a mistake frequently made in the process of managing DNS records.
(Forgetting to put a period in the right place is another common error.)
Note  To maintain serial numbers in a sensible way, use the date formatted in the following order:
YYYYMMDDxx. The tail-end xx represents an additional two-digit number starting with 00, so if
you make multiple updates in a day, you can still tell which is which.
Line 3  Line 3 in the list of values is the refresh rate in seconds. This value tells the
secondary DNS servers how often they should query the primary server to see if the
records have been updated.
Line 4  Line 4 is the retry rate in seconds. If the secondary server tries but cannot
contact the primary DNS server to check for updates, the secondary server tries again
after the specified number of seconds.
Line 5  Line 5 specifies the expire directive. It is intended for secondary servers that
have cached the zone data. It tells these servers that if they cannot contact the primary
server for an update, they should discard the value after the specified number of
seconds. One to two weeks is a good value for this interval.
Line 6  The final value (the minimum) tells caching servers how long they should wait
before expiring an entry if they cannot contact the primary DNS server. Five to seven
days is a good guideline for this entry.

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NS: Name Server
The NS record is used for specifying which name servers maintain records for this
zone. If any secondary name servers exist to which you intend to transfer zones, they
need to be specified here. The format of this record is as follows:
IN NS
IN NS
ns1.domain.name.
ns2.domain.name.
You can have as many backup name servers as you’d like for a domain—at least
two is a good idea. Most ISPs are willing to act as secondary DNS servers if they
provide connectivity for you.
A: Address Record
This is probably the most common type of record found in the wild. The A record
is used for providing a mapping from host name to IP address. The format of an A
address is simple:
Host_name
IN A
IP-Address
For example, an A record for the host serverB.example.org, whose IP address is
192.168.1.2, would look like this:
serverB
IN A
192.168.1.2
The equivalent of the IPv4 “A” resource record in the IPv6 world is called the
“AAAA” (quad-A) resource record. For example, a quad-A record for the host serverB
whose IPv6 address is 2001:DB8::2 would look like this:
serverB
IN AAAA
2001:DB8::2
Note that any host name is automatically suffixed with the domain name listed in
the SOA record, unless this host name ends with a period. In the foregoing example for
serverB, if the SOA record above it is for example.org, then serverB is understood to
be serverB.example.org. If you were to change this to serverB.example.org (without a
trailing period), the name server would understand it to be serverB.example.org
.example. org.—which is probably not what you intended! So if you want to use the
FQDN, be sure to suffix it with a period.
PTR: Pointer Record
The PTR record is used for performing reverse name resolution, thereby allowing
someone to specify an IP address and determine the corresponding host name. The
format for this record is similar to that of the A record, except the values are reversed:
IP-Address
IN PTR
Host_name
The IP-Address can take one of two forms: just the last octet of the IP address
(leaving the name server to suffix it automatically with the information it has from the
in-addr.arpa domain name), or the full IP address, which is suffixed with a period.

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The Host_name must have the complete FQDN. For example, the PTR record for the
host serverB would be as follows:
192.168.1.2.
IN PTR
serverB.example.org.
A PTR resource record for an IPv6 address in the ip6.arpa domain is expressed
similarly to the way it is done for an IPv4 address—in reverse order. But unlike the
normal IPv6 way, the address cannot be compressed or abbreviated and is expressed in
the so-called reverse nibble format (four-bit aggregation). Therefore, for a PTR record
for the host with the IPv6 address 2001:DB8::2, the address will have to be expanded to
its equivalent of 2001:0db8:0000:0000:0000:0000:0000:0002.
For example, the IPv6 equivalent for a PTR record for the host serverB with the IPv6
address 2001:DB8::2 would be (single line broken here to fit on the page):
2.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.8.b.d.0.1.0.0.2. IN PTR
\\ serverB.example.org.
MX: Mail Exchanger
The MX record is in charge of telling other sites about your zone’s mail server. If a host
on your network generates an outgoing mail message with its host name on it, someone
returning a message would not send it back directly to that host. Instead, the replying
mail server would look up the MX record for that site and send the message there
instead. MX records are used, for example, when a user’s desktop named pc.domain.
sends a message using its PC-based mail client/reader (which cannot accept SMTP
mail); it’s important that the replying party have a reliable way of knowing the identity
of pc.domain.name’s mail server.
The format of the MX record is as follows:
domainname.
IN MX
weight Host_name
The domainname. is the domain name of the site (with a period at the end, of course);
the weight is the importance of the mail server (if multiple mail servers exist, the one
with the smallest number has precedence over those with larger numbers); and the
Host_name is, of course, the name of the mail server. It is important that the Host_
name have an A record, as well.
Here’s a sample entry:
example.org.
IN
MX
10
smtp1
IN
MX
20
smtp2
Typically, MX records occur close to the top of DNS configuration files. If a domain
name is not specified, the default name is pulled from the SOA record.
CNAME: Canonical Name
CNAME records allow you to create aliases for host names. A CNAME record can be
regarded as an alias. This is useful when you want to provide a highly available service
with an easy-to-remember name, but still give the host a real name.

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Another popular use for CNAMEs is to “create” a new server with an easy-to-
remember name without having to invest in a new server at all. For example, suppose
a site has a web server with a host name of zabtsuj-content.example.org. It can be argued
that zabtsuj-content.example.org is not a very memorable or user-friendly name. So
since the system is a web server, a CNAME record or alias of “www” can be created for
the host. This will simply map the user-unfriendly name of zabtsuj-content.example.
org to a more user-friendly name of www.example.org. This will allow all requests that
go to www.example.org to be passed on transparently to the actual system that hosts
the web content—zabtsuj-content.example.org.
Here’s the format for the CNAME record:
New_host_name
IN CNAME
old_host_name
For example, for our sample scenario described earlier, the CNAME entry will be
zabtsuj-content
IN
A
192.168.1.111
www
IN
CNAME zabtsuj-content
TXT and RP: The Documentation Entries
Sometimes it’s useful to provide contact information as part of your database—not just
as comments, but as actual records that others can query. This can be accomplished
using the TXT and RP records.
A TXT record is a freeform text entry into which you can place whatever
information you deem fit. Most often, you’ll want to put only contact information
in these records. Each TXT record must be tied to a particular host name. Here’s an
example:
serverA.example.org.
IN TXT "Contact: Admin Guy"
IN TXT "SysAdmin/Android"
IN TXT "Voice: 999-999-9999"
The RP record is created as an explicit container for a host’s contact information.
This record states who is the responsible person for the specific host. Here’s an
example:
serverB.example.org.
IN RP admin-address.example.org. example.org.
As useful as these records may be, they are a rarity these days, because it is
perceived that they give away too much information about the site that could lead to
social engineering–based attacks. You may find such records helpful in your internal
DNS servers, but you should probably leave them out of anything that someone could
query from the Internet.

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DHCP
Manually configuring IP addresses for a handful of systems is a fairly simple task.
However, manually configuring IP addresses for an entire department, building, or
enterprise of heterogeneous systems can be daunting.
DHCP can assist with these tasks. A DHCP client machine can be configured to
obtain its IP address from the network. When the DHCP client software is started, it
broadcasts a request onto the network for an IP address. If all goes well, a DHCP server
on the network will respond, issuing an address and other necessary information to
complete the client’s network configuration.
Such dynamic addressing is also useful for configuring mobile or temporary
machines. For example, road warriors who travel from office to office can easily connect
their machines to the wireless or wired local network and obtain an appropriate address
for their location.
DHCP is a useful tool for dynamically configuring the addresses for large groups of
machines or mobile workstations. Since DHCP is an open protocol, the architecture and
platform of the server and the client are irrelevant.
Note  DHCP is a standard. Thus, any platform that properly implements the standard can
communicate with other DHCP servers and clients regardless of their native platform.
  So, for example, a wireless client running Windows, or a Linux or Macintosh OS, can be
configured to use DHCP and obtain their configuration information from a proprietary but compliant
wireless access point that is also acting as a DHCP server. The Windows-, Linux-, or Macintosh-
based clients will not necessarily know or care that their IP configuration information is being
provided by some other platform.
The Mechanics of DHCP
When a client is configured to obtain its address from the network, it asks for an
address in the form of a DHCP request. A DHCP server listens for client requests. Once
a request is received, it checks its local database and issues an appropriate response,
which always includes the address and can include name servers, a network mask, and
a default gateway. The client accepts the response from the server and configures its
local settings accordingly.
The DHCP server maintains a list of addresses it can issue. Each address is issued
with an associated lease, which dictates how long a client is allowed to use the address
before it must contact the server to renew the lease. When the lease expires, the client is
not expected to use the address any more. And as such, the DHCP server assumes that
the address has become available and can be put back in the server’s pool of addresses.
The server can be configured to issue any free address from a pool of addresses or
to issue a specific address to a specific machine.

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DHCP Server
The DHCP server is responsible for serving IP addresses and other relevant information
upon client request. Since DHCP is broadcast-based, a server will have to be present on
each subnet for which the DHCP service is to be provided.
Options
Currently, the DHCP server supports more than 60 network configuration parameters
(or options) to DHCP clients.
Table 9-1 shows the most commonly used DHCP options.
DHCP Client
The DHCP client is the software component used to talk to a DHCP server described in
the preceding section.
Countless platforms exists that implement the DHCP client functionality—wireless
access points (WAPs); Windows, MAC, and Linux systems; wireless PDAs, network
printers, and phones, to name a few.
When the client is invoked, it will attempt to obtain an address from an available
DHCP server and then configure its networking configuration accordingly.
DHCP Relay
As already mentioned, a DHCP client normally operates by sending out broadcast
messages. By design, routing devices do not normally forward broadcast messages.
Routers stop broadcasts in their tracks. Most WAPs and wireless gateways typically
Option
broadcast-address
domain-name
domain-name-servers
host-name
routers
subnet-mask
Description
An address on the client’s subnet specified as the
broadcast address
The domain name the client should use as the
local domain name when performing host lookups
The list of DNS servers for the client to use to
resolve host names
The string used to identify the name of the client
A list of IP addresses for routers the client is to use
in order of preference
The netmask the client is to use
Table 9-1.  Common DHCP Options

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have some routing functionality built into them. These devices also often have built-in
DHCP server functionality.
It is often desirable on any wired or wireless network to closely control the devices
that can dish out IP configuration information (act as DHCP servers). This is one of the
reasons why network administrators sometimes turn off the DHCP server functionality
in WAPs and wireless gateways—to prevent them from also acting as DHCP servers.
One process that allows routers (wired and wireless) to forward DHCP requests
from clients and DHCP responses from the server is known as DHCP relay.
A simplified version of how it works is detailed next and depicted in Figure 9-6.
1. A wireless node, Node-1, is configured as a DHCP client that needs to
participate in an IP-based network.
2. Node-1 is connected to an infrastructure basic service set managed by an access
point (AP) called AP-1.
3. AP-1 is also connected to a wired network.
4. A standalone DHCP server, called DHCPd-lan, exists on the wired network.
5. The DHCP server functionality of AP-1 is turned off.
6. Node-1 sends out broadcast message. The DHCP server DHCPd-lan does not
see the broadcast message, because AP-1 has blocked it.
7. To allow Node-1 and other wireless clients to obtain IP configuration
information, AP-1 will need to be configured to relay DHCP requests.
Node-1
6
DHCP
response
1
Broadcast
DHCP
request
AP-1
5
DHCP relay messages
from
AP-1
2
Figure 9-6.  DHCP relay
4
DHCP
response
to
AP-1
3
DHCP
request
from
AP-1
DHCPd-lan

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8. AP-1 gets the broadcast DHCP request. It converts the request to a unicast
DHCP request packet.
9. AP-1 forwards the new unicast DHCP request packet to DHCPd-lan.
10. DHCPd-lan responds to AP-1 with the requested IP configuration information
(lease)
11. AP-1 then relays the new IP configuration information it just got to Node-1.
Summary
This chapter covered the following basic information about the inner workings of some
standard wireless infrastructure services:
■■ Name resolution
■■ The different DNS server types: primary, secondary, and caching servers
■■ Various DNS record types (for IPv4 and IPv6)
■■ DHCP service, which is used for providing and managing the IP configuration
information for groups of client machines or mobile workstations

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Optional Infrastructure
Services and Protocols
141

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Key Skills and Concepts
■■ Introduce some optional services and protocols that can enhance a wireless
network infrastructure.
■■ Learn about the RADIUS and Diameter protocols.
■■ Learn when to deploy RADIUS or Diameter as a part of the wireless network
infrastructure.
■■ Understand the functions and types of proxy servers.
■■ Learn when to deploy a proxy server as a part of the wireless network infra-
structure.
Chapter 9 covered some standard services that complement any wireless network
setup. This chapter continues that idea by discussing services that complement
wireless networks. Complement, in this context, means that a wireless network can
exist and function without these services, but these services nonetheless add value to the
overall wireless network infrastructure.
As with the standard services, the services discussed in this chapter work invisibly
in the background and should be transparent to the end user. The end user almost
never has to directly interact with the services or even notice their presence.
RADIUS
The Remote Authentication Dial-In User Service (RADIUS) protocol is defined in the
Internet Engineering Task Force (IETF) document RFC 2865 and used for managing
access to resources on a network. The protocol has been around for a long time and
is used in one form or another in countless applications. RADIUS does its job by
providing a means for centrally managing users, which can be in the form of a user
database that can also contain a list of requirements that must be met to grant access to
a user.
RADIUS helps to solve some of the problems and logistics issues involved with
managing large numbers of users accessing a network. RADIUS addresses these issues
by taking an approach that breaks down the problems into three areas: authentication,
authorization, and accounting.
The RADIUS protocol’s longevity is a result of its extensibility. The protocol was
designed from inception to be easily extensible so that new features can be easily
layered or added to the base protocol without disturbing existing instances of the
original protocol.
RADIUS Entities
Figure 10-1 shows the relative placement of RADIUS entities on a sample wireless network.

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143
End user
Network access server
(wireless access point)
End user
End user
Access server (AAA server)
Figure 10-1.  A sample RADIUS network
The following players are involved in any environment that implements RADIUS:
■■ End user  The entity that needs access to the network resource, such as a
wireless station (STA) that needs to join a wireless distribution system (WDS).
From the perspective of the RADIUS protocol, the end user is not necessarily
the same entity as the RADIUS client. In fact, the end user is often distinct from
the actual RADIUS client.
■■ Network access server (NAS)  The gate-keeping device that provides the
access to the network, such as a wireless access point (AP).
The end user connects to the NAS whenever it needs to access any network
resources. The NAS in turn relies on an access server to determine whether to
allow or deny access to the end user entity. The NAS is commonly known as
the RADIUS client or the authenticator.

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■■ Access server (AS)  The server component of the RADIUS protocol; also
known as the RADIUS server.
The NAS forwards end user requests to access network resources to the AS.
The AS then makes the final decision about whether to grant or deny access to
the end user.
You might be wondering why a book on wireless networking is discussing a dial-in
user service since wireless stations (STA) obviously do not need to dial into anywhere
to connect to the wireless network. The information is included for three reasons:
■■ RADIUS is just a name, and the standard governing the workings of RADIUS
was invented many years ago before wireless networks became as ubiquitous
as they are today. The name “RADIUS” served the original purpose for which
the standard was first created: to control dial-in access to networks. So, in
other words, the name no longer does the standard justice, considering all the
additional functionality and applications that have since been squeezed out of it.
■■ Wireless STAs can dial into a network, sort of. Although the STA is not using
the traditional dial-in paradigm over copper lines (cables), the STA still needs
to log in to the network.
■■ Large enterprise wireless (Wi-Fi) networks often rely on RADIUS as a
centralized way to manage user credentials and access to the network. This
helps to mitigate against some of the risks associated with using common/
shared keys or passwords among users.
AAA
AAA—authentication, authorization, and accounting—can be viewed as the framework
that implements the RADIUS protocol.
Authentication
Authentication is used to verify the identity of an entity. It is used, for example, mostly
for verifying the identity of an end user. I say mostly because authentication can
also work in the reverse direction (two-way authentication), where the entity being
authenticated also requires that the authenticator (the other entity) verifies itself.
Authentication is where it all begins. Any end user or station that needs access
to any network resource first needs to be authenticated. It starts when the end user
presents its credentials to the NAS in one of various forms, such as username, login ID,
password, hardware token, digital certificate, and so on. Authentication is considered
successful when the presented credentials have been verified to be valid.
Some popular authentication methods are discussed next.

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Password Authentication Protocol (PAP)  This is a weak authentication method. It is weak
because the user credentials are sent in clear text over network. It can be used as an
authentication measure of last resort when the entities involved cannot support any
other type of authentication scheme.
Challenge-Handshake Authentication Protocol (CHAP)  This authentication method depends
upon a shared “secret” known only to the entities involved in the schema. The secret is
not sent over the link.
The process begins after a link has been established between the two entities. The
authenticator sends out a challenge message to the other peer.
The peer responds to the challenge with a value calculated by using a one-way hash
function. Both entities should have prior knowledge of how to apply this hash function
based on the shared secret.
The authenticator also runs the same one-way hash function on the challenge and
knows what the expected value should be. If the values match, the authentication is
acknowledged; otherwise, the connection is terminated.
The authenticator entity periodically sends out a new challenge to the other peer
during the connection lifetime to help guard against compromise.
Microsoft Challenge-Handshake Authentication Protocol (MS-CHAP)  This is Microsoft’s twist
of the CHAP authentication method. MS-CHAP version 2 (MS-CHAP-V2) is the latest
iteration of the protocol.
MS-CHAP-V2 supports mutual authentication of the peers. It also has a built-in
mechanism for the authenticator to force or initiate a password change of the other peer.
Extensible Authentication Protocol (EAP)  EAP is defined in the IETF documents RFC 3748
and RFC 5247 as an authentication framework that supports multiple authentication
methods. EAP operates at the Data Link layer of the OSI reference model—this means
that EAP is not dependent on IP.
EAP is merely a framework and not an authentication method by itself. Instead, it
is a framework around which other authentication mechanisms can be designed. As
implied by its name, EAP was designed with extensibility in mind, and this makes
it very future-proof. As newer authentication mechanisms are developed and as
vulnerabilities are found in older authentication methods, newer protocols can be
designed that still use EAP as their base foundation.
EAP is used extensively in the de-facto wireless security protocols, such as Wi-Fi
Protected Access (WPA and WPA2). EAP can also be used in security protocols that
secure wired networks, such as IEEE 802.1X.
Authorization
The authorization component of AAA deals with permission issues. It specifies what
an authorized end user can do with a given resource after the end user has been

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successfully authenticated. The criteria used for granting authorization can be based on
end user physical location, time of day, group membership, connection type, and other
factors.
Accounting
The accounting aspect of the AAA framework is used for keeping track of the end
user’s usage or consumption of the network resources.
Accounting can also be used for purposes of capacity planning, auditing, billing, or
cost allocation, as well as to track other usage statistics, such as successful or failed user
login attempts and successful or failed user authorization attempts.
Note  RADIUS is based on the User Datagram Protocol (UDP). The authentication component of
RADIUS runs off the UDP port 1812, and the accounting component runs off the UDP port 1813.
When to Use RADIUS
So how does a wireless network administrator of great repute know when to include
RADIUS as part of his or her infrastructure arsenal? The following checklist might help
answer this question:
■■ Consider RADIUS when you need to manage and maintain a large number of
users using the wireless network from a central location.
■■ Consider using RADIUS to complement any of the enterprise-grade wireless
security solutions that can take advantage of it.
■■ Consider RADIUS when you need to keep track of wireless users for
accounting and billing purposes.
■■ Consider using RADIUS when you need to enforce or define advanced policy–
based features such as time-dependent access for the users of the wireless
network.
■■ Consider using RADIUS when the wireless network is meant for the public
use—such as in public wireless hotspots.
■■ Consider using RADIUS when a RADIUS server is already being used on the
wired network, especially when the integration can be done easily, seamlessly,
and in a beneficial way.
■■ Consider using RADIUS when you are managing a large number of disparate
wireless clients that are running on different platforms, such as Linux,
Windows, Macintosh, UNIX, BSD, and so on. This can help to reduce the
impact of the quirks that might exist in the implementation of authentication,
authorization, and encryption solutions within each vendor’s platform.
RADIUS is a standards-based protocol, and any platform that claims to
support RADIUS must support the standard.

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Popular RADIUS Implementations
Several vendors and groups have created their own implementations of the RADIUS
protocol. Depending on the level of user adoption of the implementation, some of these
may no longer be under active development or maintenance but may still be in use on
various network deployments:
■■ The FreeRADIUS Project (http://freeradius.org)
■■ Network Policy Server (http://technet.microsoft.com/en-us/network/
bb629414.aspx), a built-in component in Microsoft Windows Server.
■■ BSDRadius (www.bsdradius.org)
■■ Cisco Secure Access Control Server (www.cisco.com)
■■ Juniper Networks Steel-Belted Radius series (www.juniper.net)
Diameter
It only makes sense that if we have a protocol named RADIUS, there should be a
corresponding protocol named Diameter!
The Diameter protocol is the successor to the RADIUS protocol. It was conceived
as a way to ease the demands being placed on the older RADIUS protocol and was
deemed necessary because of the continued development and evolution of numerous
access technologies that RADIUS might struggle to keep up with. Diameter was
designed to be as backward-compatible with RADIUS as possible. The feature sets and
capabilities of newer NAS devices have also increased substantially, thereby requiring
support for similar features on the access server (AS).
Diameter is also used to provide AAA services. The inner workings of the protocol
are specified in IETF RFC 3588.
The following features of the Diameter protocol distinguish it from the older
RADIUS protocol:
■■ Diameter uses reliable transport protocols such as Transmission Control
Protocol (TCP) and Stream Control Transmission Protocol (SCTP).
■■ It has built-in support for network or Transport layer security, such as Internet
Protocol Security (IPSec) and Transport Layer Security (TLS).
■■ It offers better roaming support.
■■ Diameter has built-in fail-over support.
■■ Diameter supports automatic peer discovery and configuration by using
special DNS records.
■■ Diameter supports Mobile IP, which allows a mobile node to change its point
of attachment to the network while maintaining its original IP configuration.

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You should consider using Diameter in any of the scenarios discussed in the “When
to Use RADIUS” section, as well as when you need to future-proof the infrastructure
components of the wireless network. Even though RADIUS is a legacy protocol, it is
still very well entrenched in many IT environments, but the time will come when it will
no longer be capable of handling newer technology requirements.
Diameter Entities
The following players are important in any environment that implements the Diameter
protocol:
■■ End user  The entity that needs to access the network resource, such as a
wireless STA that needs to participate in a WDS.
■■ Diameter client  The Diameter client generates and receives requests and
responses on behalf of the user—for example, a network access server (NAS)
such as a wireless access point (WAP).
■■ Diameter server  Handles AAA requests.
■■ Diameter peer  Used to describe the relationship between Diameter entities,
wherein one Diameter node has a direct transport connection with another.
For example, a Diameter client acting as a NAS can be peers with a Diameter
server with which it is connected.
■■ Diameter node  Any entity that implements the Diameter protocol and
functions either as a Diameter client, Diameter proxy, or Diameter server.
■■ Diameter proxy  An entity that helps to forward requests and responses
between other Diameter nodes.
Proxy Server
Proxy servers come in all shapes, forms, and sizes, but they all have a few things in
common—particularly with regard to their definition. A proxy server is software or
hardware that acts as a broker or intermediary for requests from clients that need
access to certain network resources. Proxy servers can help make your job much easier,
can help make your users and upper management happier, and can help improve the
bandwidth usage on wireless networks.
A proxy server works by receiving requests from the client, and then forwarding
the client requests to the appropriate server that is hosting the resource. The proxy
server also receives the responses from the server and forwards the responses back to
the originating client. While all of this is going on, the proxy server may also be doing
other things with the requests and responses:
■■ It can deny access to a given resource.
■■ It can speed up the entire communication between the client and server
through a process called caching.

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■■ It can filter or sanitize the requests and responses from clients to servers, or
vice versa.
■■ It can offer some form of anonymity to clients by not directly exposing them to
the server or to other possibly hostile external networks.
■■ It can reformat client or server requests or responses from one form to another.
Types of Proxy Servers
Proxy servers differ when it comes to the specific type of resource to which they are
brokering access. Several types of proxy servers are based on the resource types they
are proxying.
Web Proxy Server  One of the most common types of proxy servers, the web proxy
server’s main purpose is to proxy Web or other Hypertext Transfer Protocol (HTTP)
type requests. The end objective of these types of proxy servers can be multifaceted.
For example, it may function to control user access to web resources on a network,
or it may be used to speed up access to web resources by caching the resources
locally.
These proxy servers can also be used for changing, manipulating, or translating
content from one form to another, which may be necessary when, for example, the end
client cannot support or make use of the resource in its original form. A web proxy
server can also be used to reformat traditional web pages to a format that is more
suitable for viewing on devices such as mobile devices.
Content-filtering Proxy Server  Content-filtering proxy servers can be used for various
purposes but are often used in exercising administrative control over the resources that
the end user accesses.
They can also be used in restricting user access to certain web content, for forcing
users to access specific content, or for enforcing compliance with network or business
policies, for example.
Caching Proxy Server  Caching proxy servers are used for caching or storing copies of
frequently accessed resources locally on the proxy server. This speeds up user access to
these resources.
Transparent Proxy Server  These types of proxy servers are designed to work transparently
in the background without any end user (or client) interaction. Because no changes need
to be made to the client end, the client does not need any special support for the proxy
capabilities. Transparent proxy servers are also useful in large networks where it may not
be practical or feasible to reconfigure all the clients individually to use the services of the
proxy server. Transparent proxy servers make it more difficult to bypass the client, which
offers the administrator better control.

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When to Use a Proxy Server
A wireless network administrator should consider introducing a proxy server into a
wireless network if any of the following scenarios apply:
■■ You need to save money on network bandwidth. If your ISP charges you
based on the amount of data transferred (per megabyte or per gigabyte) over
their network, having an in-house proxy server will help reduce the total data
transferred over your provider’s network. The proxy server will try to reuse
content from its local cache for your local network users instead of each user
connecting to the Internet every time he or she needs the same data.
■■ You want to improve user experience when they’re accessing external content.
Content retrieval will appear faster for some data thanks to the proxy server.
■■ You need a way to keep track (or logs) of what the wireless network users are
accessing via the network. This may be necessary for legal or administrative
reasons.
■■ You need to control what the wireless network users are doing via the network.
This may be necessary for legal or administrative reasons.
■■ You need to provide a simple method to authenticate users before they access
web-based resources via your network.
Popular Proxy Server Implementations
Several vendors and groups have created their own proxy server products, including
the following:
■■ Squid (www.squid-cache.org)
■■ Microsoft Forefront Threat Management Gateway (www.microsoft.com/
forefront/threat-management-gateway)
■■ Wingate (www.wingate.com)
■■ Tor (www.torproject.org)
Summary
You’ve learned about some nonstandard or optional components that can be found
on wireless network infrastructures. They are considered non-standard or optional
because their use is not essential to the operation of the wireless network. In general,
these services or protocols are nice to have and help to make your job and life a little bit
easier—and they make the network users more productive and happier as well.

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Key Skills and Concepts
■■ Learn about cryptography and cryptographic concepts and terms.
■■ Learn about algorithms and ciphers.
■■ Review some cipher examples and implementations.
■■ Review the Extensible Authentication Protocol (EAP) framework.
■■ Review IEEE 802.11i and some considerations for deploying an IEEE 802.11i
network.
Wireless-based communication systems that function over the radio frequencies
have the following characteristics:
■■ Invisible  Wireless communication travels over invisible airwaves.
■■ Almost boundless  Restricting or constraining the boundaries of wireless
communications can be difficult, thereby making it possible for the
communications to end up in unintended locations.
■■ Easy to monitor and observe using the proper equipment  Preventing
unwanted parties from monitoring or observing the communications can be
difficult.
For these reasons, wireless communications have a notoriety of being insecure.
Yet wireless communications are indispensable, because they offer us so much
convenience. The best we can hope for is to try to find ways to manage and mitigate
their undesirable characteristics.
This chapter examines some of the ways that have been developed to make wireless
communications more secure. Note that making advancements in securing wireless
communications, as in other IT fields, is like trying to hit a moving target. As a result,
newer and better methods are constantly being developed as weaknesses or vulnerabilities
are discovered in existing solutions.
Let’s start by taking a brief look back into the past; then we’ll work our way up to
the present methods used for securing wireless communications.
Security Background
We know that communication occurs between two or more entities; the trouble with
wireless communications is that, when one entity tries to communicate with another
entity, a third (or more) outside entity can listen in if the proper security techniques
haven’t been implemented to protect the communication. In other words, it takes effort
to secure wireless communications to prevent uninvited entities from listening in.

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A few options are available for achieving security, including the following:
1. We don’t communicate at all.
2. We communicate but restrict all communications to self.
3. We communicate but try to be careful with whom or what we communicate.
4. We communicate but try to be careful about the nature of what we
communicate.
5. We communicate but with the knowledge that our communications may not
be perfectly secret and accept the risks while trying to mitigate them as best as
we can.
Past and current approaches to securing wireless communications tend to use a
mixture of options 3, 4, and 5 to do the job.
The third option tackles the issues of communicating securely in a wireless network
via means of authentication—either one or all the parties involved in the communications
channel try to verify the others’ identities.
One approach that fits the fourth option for facilitating secure wireless communications
is using cryptographic manipulation and transformation. Cryptographic methods can be
used to disguise or manipulate the communication so that it is visible or useful only to the
party for which it is intended but useless to any other party.
The fourth option raises other questions and issues. For example, how can you
protect or secure something that you can’t see? To answer this question, we first have
to understand the nature and components of the wireless “frames” being transmitted.
Chapter 6 discussed the wireless Media Access Control (MAC) frame types used on
IEEE 802.11 networks.
Note  Remember that the IEEE 802.11 standard concerns itself with the workings of the Physical
layer (PHY) and the MAC sublayer of the Open Systems Interconnect (OSI) reference model. For
this reason, most of the common standards-based methods and solutions for securing wireless
networks are implemented at the MAC sublayer.
Let’s review the MAC frame types:
■■ Control frames  These frame types are very important for all wireless
communications and are used to support the delivery of the other
(management and data) MAC frame types. They are the most basic frame type.
It is important that the information in the control frames be visible to all the
nodes in a wireless network; it is not secret in any way.
■■ Management frames  These frame types are used by wireless nodes
to join or discontinue their membership in the wireless network and for
other miscellaneous housekeeping purposes. Keeping the content of the
management frames secret may sometimes be important.

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■■ Data frames  These frame types are used for transporting the data payload.
They might, for example, contain the information that we are trying to protect
and transmit.
Cryptographic techniques can be used to protect information in management and
data frames. The following sections discuss security concepts and techniques that can
be used in securing wireless communications.
Security Services
Regardless of the solution used, any good security solution(s) employed in wireless
networks should satisfy the basic needs of authentication, confidentiality, and integrity.
■■ Authentication  Ensures that the entities that need to communicate are truly
who they say they are; can include authorization, which allows the entities to
communicate on the network after having authenticated successfully.
■■ Confidentiality  Ensures that any information transmitted or shared between
the communicating entities remains confidential or inaccessible to any
unauthorized or outside entities.
■■ Integrity  Preserves the sanctity of the information communicated between the
authorized entities. The contents of the communication must not be corrupted,
destroyed, or altered in any way before reaching its intended destination.
Each security solution satisfies these three basic needs in varying degrees: for
example, one solution might provide authentication services but is insufficient at
providing confidentiality services; another solution may provide confidentiality and
integrity services but cannot provide authentication services. In other words, we would
find that in the real world, no security solution is perfect.
Cryptographic Concepts and Terms
Cryptography can be defined as the act or art of writing in secret characters. In technical
jargon, it refers to the science and study of encrypting and decrypting information,
identity verification and authorization, digital signatures, integrity checking, and secure
computation. The following terms related to cryptography will aid in your understanding
of later sections of this chapter.
Plain-text
Plain-text describes the unencrypted payload; it refers to the original bits and bytes as
they exist before they undergo any type of cryptographic transformation.
Note  The term “plain-text” is somewhat of a misnomer, because the word “text” here does not
necessarily refer to regular text—it can be any combination of bits and bytes.

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If privacy or secrecy were not of concern in wireless communication systems, the
steps involved in sending and receiving data would be very simple and straightforward:
We’d simply start with plain-text at the sender end, that plain-text would be transmitted
as is, and then we’d end up with plain-text at the receiver end. However, because secure
communications are required between senders and receivers, encryption is added to
the mix. We start off with plain-text at the sender end, the plain-text then undergoes
some cryptographic transformation and manipulation (becomes cipher-text), the cipher-
text is transmitted, the receiver gets the cipher-text and passes it through another
cryptographic transformation or manipulation, and, finally, if the transformation process
is successful, the original plain-text is derived and viewed by the receiver.
Note  “Clear text” is another name for plain-text. It also means that the data is unencrypted.
Encryption and Decryption
Encryption is the transformation of information from one form (plain-text) to another
(cipher-text). Encryption makes cipher-text nearly impossible to decipher without the
appropriate knowledge, or key.
Decryption, the opposite of encryption, is the transformation of encrypted
information (cipher-text) back into an intelligible form (plain-text).
Key
A key in cryptology is similar to a key we use for locking and unlocking things in
everyday life. In cryptography, keys are the bits and bytes used in the process of
encryption and decryption. In this case, a key is a very large number that has special
mathematical properties. Breaking into an encryption scheme depends on knowledge
of the key or the ability to discover the key. The larger the key, the more difficult it is to
discover.
Low-grade encryption uses 56 bits—this means 256 possible keys. The following
might help provide a sense of scale:
■■ 232 is equal to 4,294,967,296 (more than 4 billion).
■■ 248 is equal to 281,474,976,710,656.
■■ 256 is equal to 72,057,594,037,927,936 (more than 72,057 trillion).
While this seems like a significant number of possibilities, present-day computers
have enough processing power to make discovery a possibility and a cause for real
concern—especially when low-grade encryption is in use.
Keyspace
The keyspace is related to the key used for encryption and decryption. The keyspace
refers to the range of possible values that can be used in the key. The wider the range of
the keyspace, the more difficult it can be to break or compromise the encryption.

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Keystream
A keystream is a stream of random or pseudo-random data that is combined with the
plain-text to produce cipher-text. Different mathematical or logic operations can be
performed on the keystream in combination with the plain-text to generate the cipher-
text. The keystream is not necessarily related to the key or the safeguarded information
in any way.
The following logic operations can be performed on the keystream and plain-text
(among others):
■■ Conjunction (AND)
■■ Disjunction (OR)
■■ Negation (NOT)
■■ Not both (NAND)
■■ Neither Nor (NOR)
■■ Exclusive OR (XOR)
Note  Pseudo-random numbers are a series of numbers that are similar to random numbers but
cannot be defined as being completely random, because they are generated from a relatively small
set of initial values. Their scope is limited or finite.
Exclusive OR (XOR)
An XOR is binary logic operation: it requires two inputs or operands. The
operands are the values of propositions (a statement in which something is
confirmed as true or denied as false). An XOR operation between two operands
returns a true value if only one of its conditions is true.
An XOR is used as the basis for encryption in Wired Equivalent Privacy
(WEP), which is discussed in a bit later in this chapter.
The following examples show the results of performing an XOR operation on
two numbers—1 and 0:
■■ 1 XOR 1 = 0
■■ 1 XOR 0 = 1
■■ 0 XOR 1 = 1
■■ 0 XOR 0 = 0
Where 0 = False and 1 = True.

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Algorithm
An algorithm is an established computational approach for solving a problem in a finite
number of steps that are easily duplicable in the same manner given the same set of
parameters. Technically, the algorithm must generate a result after a finite number
of steps. In the world of cryptography, there are currently two classes of algorithms:
symmetric and asymmetric algorithms.
Symmetric Encryption Algorithms
Symmetric algorithms often use the same key for encryption and decryption. In
symmetric encrypted algorithms, the key size is directly correlated with the strength
of the encryption, so a large key size used with a good algorithm will be more difficult
to break than a small key size. Symmetric algorithms are best suited for providing
confidentiality requirements of a security system.
This type of algorithm is also referred to as a “secret key–based algorithm” because
its mode of operation depends on a secret—the “key”—that is shared between the
entities that need to communicate securely. It is therefore important that the secret,
or key, is well protected at all times. The sharing of this key is also one of the main
weaknesses of symmetric encryption algorithms. The other weakness of the symmetric
algorithms is in the logistics of how the key is distributed to the parties that need it.
Symmetric algorithms are generally computationally less demanding when compared
with asymmetric algorithm (discussed next) and as such tend to execute faster.
Following are examples of symmetric algorithms:
■■ Advanced Encryption Standard (AES)
■■ Triple Data Encryption Algorithm (3DES)
■■ Blowfish
■■ Carlisle Adams and Stafford Tavares v5 (CAST5)
■■ International Data Encryption Algorithm (IDEA)
■■ Twofish
Asymmetric Encryption Algorithms
This class of algorithms employs a different key for encryption and decryption.
Furthermore, the decryption key cannot be derived from the encryption key. This type
of algorithm is also referred to as a “public-private key–based algorithm.” The public
portion of the name stems from the fact that the public key can be known by anybody
(it’s not a secret), but the private key portion should be a secret. The public and private
keys are, however, mathematically related.
Algorithms that use asymmetric encryption are computationally more demanding
than symmetric algorithms and as such are much slower in execution. The ease of
distribution and management of the keys used for encryption and decryption are better
than symmetric-based solutions. Some examples of asymmetric algorithms include
Diffie-Hellman, ElGamal, and Merkle-Hellman Knapsack.

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Public-Private Key Cryptography  Asymmetric encryption and decryption algorithms
rely on a technology called public-key cryptography, which works similarly to a safe
deposit box at the bank: you need two keys to open the box, or at least multiple
layers of security checks must be used. With public-key cryptography, you need two
mathematical keys: a public one and a private one. Your public key can be published
on a public web page, printed on a T-shirt, or posted on a billboard in the busiest part
of town. Anyone who asks for it can have a copy. On the other hand, your private key
must be protected to the best of your ability. This piece of information makes the data
you want to encrypt truly secure.
Every public key/private key combination is unique. So the basic principle of
public-private key cryptography is that data encrypted with the public key can be
decrypted using only the private key. Furthermore, encrypting with the private key can
serve as a digital signature.
The actual process of encrypting data and sending it from one person to the next
requires several steps. We’ll use the popular “Alice and Bob analogy” to go through the
process one step at a time as they both try to communicate with one another in a secure
manner. Figures 11-1 through 11-5 illustrate a simplified version of the actual process.
Notice that at no point was the secret (private) key sent over the network. Once the
data was encrypted with Bob’s public key and signed with Alice’s private key, the only
pair of keys that could decrypt and verify it were Bob’s private key and Alice’s public
key. Thus, if someone intercepted the data in the middle of the transmission, he or she
wouldn’t be able to decrypt the data without the proper private keys.
To make things even more secure, asymmetric encryption algorithms encourage
implementations to change the session key regularly through a randomly generated,
symmetric key for encrypting the communication between the sender and the receiver.
Using sessions keys ensures that the data stream gets encrypted differently every few
minutes. So even if someone happened to figure out the key for a transmission, that
miracle would be valid for only a few minutes, until the keys changed again.
Cipher
The cipher is any method that is used for encryption and decryption. The meaning of
the words “cipher” and “algorithm” can often be interchanged, since they both mean
Alice
Network
Figure 11-1.  Alice fetches Bob’s public key.
Bob
Public key

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Alice
Bob
Bob’s public key
+ Alice’s private key
+ Data
= Encrypted data
Network
Figure 11-2.  Alice uses Bob’s public key to encrypt the data, and she uses her private key to
sign the data.
Alice
Bob
Encrypted data
Network
Figure 11-3.  Alice sends the encrypted data to Bob.
Alice
Bob
Public key
Network
Figure 11-4.  Bob fetches Alice’s public key.
Alice
Bob
Network
Alice’s public key
+ Bob’s private key
+ Encrypted data
= Decrypted data
Figure 11-5.  Bob uses his private key to decrypt the data, and he uses Alice’s public key to
verify the data.

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the same thing. A cipher is the algorithm or function that creates the encryption and
the decryption. These algorithms can range in complexity from the simple and elegant
to the incredibly complicated and convoluted. Note that complicated ciphers do not
always yield the strongest or most secure encryption. In fact, the inner workings of a
good cipher system should lend itself to scrutiny and thus improvement.
Depending on their mode of implementation, ciphers can be categorized in several
ways—for example, concealment ciphers versus running key ciphers, substitution
ciphers versus transposition ciphers, or stream ciphers versus block ciphers.
Concealment Ciphers vs. Running Key Ciphers
Both of these ciphers types are early or classical methods for producing cipher-text.
Concealment ciphers work by concealing or hiding the plain-text message within
another message.
Running-key ciphers rely on a simple square table of alphabets called a “tabula recta”
and a chunk of text from a previously agreed-upon source called a “polyalphabetic
source” (such as a book). The tabula recta is a table made up of rows of the alphabet,
with each row computed by shifting the preceding letter to the left. The plain-text is
substituted with chunks of text from the polyalphabetic source, and the cipher-text is
then derived by the value in tabula recta. The “key” here is the polyalphabetic source.
Table 11-1 shows a truncated tabula recta.
Substitution Ciphers vs. Transposition Ciphers
Substitution ciphers work by replacing/substituting parts or the whole of the plain-text
with something else. A key is used to predetermine how the substitution should take
place.
Transposition ciphers, on the other hand, do not rely on substitution; instead, parts
of the plain-text are moved or juggled around to hide the meaning of the original plain-
text.
Stream Ciphers vs. Block Ciphers
Stream ciphers are a special class of ciphers in which the encryption and decryption
algorithm is applied to the individual bits or bytes of the plain-text. The algorithm
works by combining the plain-text bits or bytes with a pseudo-random bit stream, one
bit or byte at a time.
Stream ciphers are especially well suited for encrypting and decrypting the type of
data that is used in network communication systems—data in transit. Some examples
of a stream cipher algorithm are the RC4 cipher and the A5 algorithm that is used in
cellular-based Global System for Mobile (GSM) communications.
Block ciphers are another special class of ciphers that perform their magic on blocks
of plain-text instead of individual bits. When necessary, the plain-text can be divided
into blocks and the algorithm is applied to the individual blocks.

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A B C DE F G H I J K L MNOP QRS T U V WXY Z
A A B C D E F G H I J K L MNOP QRS T U V WXYZ
B B C DE F GHI J KL MN OP QR S T U V WX YZA
C C D E F GHI J KL MN O P QR S T U V WX Y Z AB
D D E F G HI J K L MN O P Q R S T UV WX Y Z AB C
Table 11-1.  Tabula Recta

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Block ciphers define different “operating modes.” These operating modes serve as
a sort of blueprint for the algorithm to perform the actual encryption or decryption.
Following are some popular operating modes for block ciphers:
■■ Electronic codebook mode (ECB)  This mode is quite simple and is also prone
to several weaknesses. It relies on the use of a fixed “code” book for encrypting
data blocks. The fact that a given plain-text and key combination will always
yield the same cipher-text is one of its weaknesses.
■■ Cipher-block chaining mode (CBC)  This mode operates by using (or
chaining) the cipher-text extracted from the preceding block to encrypt the
next block of data. This is probably the most popular and widely used mode of
operation for block ciphers.
■■ Counter mode (CM)  This mode operates by using an initialization vector
(IV) counter that increments for every block of plain-text to be converted to
cipher-text. Block ciphers that operate in this mode are generally very fast in
executing.
■■ Output feedback mode (OFB)  This mode is best suited for encrypting
smaller chunks of plain-text at a time, because it can emulate the behavior of
stream ciphers.
Cipher Examples
Following are several examples of ciphers:
DEA (DES)  A very long time ago, the National Institute of Standards and Technology
(NIST) realized that sensitive data needed to be protected in a standardized way. The
Data Encryption Standard (DES) was born, and this standard was implemented with
the Data Encryption Algorithm (DEA).
Major parts of the inner workings of DEA were invented by the IBM corporation; it
was originally known as the Lucifer cipher within IBM. NIST accepted, modified, and
re-branded the Lucifer cipher.
DEA is a symmetric block cipher. This means that it works by performing a series of
transpositions and substitutions on blocks of the plain-text. Its symmetric aspect means
that it uses the same key for encryption and decryption. The key size used in DEA is
64 bits long.
Note  IBM’s original Lucifer cipher from which DEA was derived used 128-bit-long keys. For
whatever reasons, NIST chose to downgrade the key length to 64 bits.
DES and its associated algorithm were in use for a long time in many applications,
and eventually NIST deployed a newer and stronger algorithm. NIST determined that
it was time to retire the older DEA partly because of the vastly increased computing
capabilities of the then-current computer systems. In fact, the second shoe finally
dropped when the efficacy of DES was compromised in 1998.

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3DES (AES)  NIST called for the development and submission for a newer, better, and
stronger method of protecting sensitive information after it was decided that the aging
DEA was no longer sufficient, and the Advanced Encryption Standard (AES) was born.
AES was implemented with the 3DES (pronounced Triple-DES), also known as the
Rijndael Algorithm, which is a play of the names of its two inventors, Joan Daemen and
Vincent Rijmen.
Like its predecessor, 3DES is also a symmetric block cipher, but it supports larger
block sizes than DES. Specifically, it supports plain-text block sizes of 128, 192, and
256 bits, as well as corresponding key lengths of 128, 192, and 256 bits for encryption.
Generating cipher-text from plain-text using 3DES is generally a more computationally
demanding process when compared to DES. This means that more powerful hardware is
required when working with 3DES.
RC4  Rivest Cipher 4 (RC4), named after its inventor, Ron Rivest, is a popular and
widely used cipher. It uses symmetric keys and is a stream cipher. The key size or
length used in RC4 is variable but should be between 1 and 255 bytes.
Being a stream-based cipher, RC4 is quite fast in its execution and not too
computationally demanding. Because it is stream-based, encryption and decryption
operate on the individual bits (or bytes) of the plain-text.
Cipher Implementations
So far we’ve reviewed algorithms, cipher-text, plain-text, and ciphers, and you might
be wondering of what practical use any of these things are to a wireless network
administrator.
In the following sections, we will look at the practical implementations of some of
the cryptographic concepts discussed thus far—as they pertain to wireless network
administration.
Wired Equivalent Privacy Protocol
When the IEEE 802.11 standard was being developed, it was a necessity that some
method be required for securing the communications that use radio frequency (RF)
as a medium. The proposed and implemented solution was the Wired Equivalent
Privacy (WEP) protocol. The phrase “wired equivalent” refers to the intention and goal
for WEP, which was to secure communications in a wireless network in ways that are
equivalent to those achieved in wired networks.
Under the hood of WEP is the RC4 cipher. WEP is a living and practical example of
a textbook cipher (RC4).
The following steps show a simplified version of how WEP works:
1. The entities (nodes) that want to communicate securely in a wireless
distribution systems agree to use WEP to secure their communications.

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2. Since WEP is based on RC4, which uses symmetric keys, a key (common secret)
is therefore needed. The nodes choose and agree on a common secret key to be
used.
3. The plain-text message to be sent over the wireless medium is created by the
node.
4. The plain-text data is passed through a hashing algorithm to obtain a
checksum.
5. The checksum is appended to the plain-text data.
6. A 24-bits-long initialization vector (IV) is generated and appended to the secret
key. This results in a stream of data that is generated and run through the RC4
pseudo-random number generator to form a keystream that is equal in length
to the original plain-text/checksum from step 5.
7. An XOR operation is performed on the resulting keystream and the plain-text/
checksum combination obtained from step 5.
8. The result of the XOR operation is the cipher-text or encrypted message.
9. The cipher-text is transmitted over the wireless medium to the receiving node,
which then proceeds to decrypt the data.
WEP is considered a deprecated method for securing wireless networks. WEP
is easily broken and should not be relied on as a method for securing wireless
communications. WEP is also vulnerable to brute-force attacks, dictionary attacks,
reinjection attacks, and attacks that take advantage of its use of IV.
Wi-Fi Protected Access
WPA is the successor to the WEP protocol. After the weaknesses in the WEP
implementations were discovered, WPA served as a stop-gap measure for securing
wireless networks while the IEEE 802.11 standards committee developed a more
robust and permanent solution. The inner workings of WPA were specified in the early
versions of the IEEE 802.11i standard.
Two flavors of WPA exist: Temporal Key Integrity Protocol WPA (TKIP/WPA) and
Advanced Encryption Standard WPA (AES/WPA).
TKIP/WPA
TKIP is one of the components of the IEEE 802.11i standard that attempts to address
some of the vulnerabilities discovered in the WEP protocol. TKIP is used for generating
random values that can be used along with the encryption algorithm to produce better
encryption relative to WEP. TKIP also addresses an important aspect of a cryptographic
solution that was sorely missing in WEP—key management. Specifically, WEP was
incapable of dynamic key management. Proper key management schemes make sure
that the cryptographic keys are kept safe from unauthorized parties.

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A guiding principle behind the development of TKIP was to provide a solution that
would not be too much of a radical departure from the existing WEP deployments.
TKIP was designed so that original equipment manufacturers (OEM) of networking
hardware could easily apply the new changes and improvements via software or
firmware updates, without requiring the numerous/existing WEP deployments to
make major changes to their current infrastructure.
So the “marketing name” for TKIP is WPA, and TKIP/WPA is endorsed by the
Wi-Fi Alliance, which comes in the form of a certification program. The Alliance
guarantees interoperability and compliance in products that have passed its
certification requirements.
Underneath TKIP is still the RC4 algorithm—albeit a new and improved
implementation. Exploitable vulnerabilities have been discovered in TKIP/WPA
solution.
Tip  The version of WPA that is targeted and well suited for the home user or SOHO market is
called WPA Personal, WPA Pre-shared Key (WPA-PSK). And the version targeted for the enterprise
market is called WPA Enterprise.
  The pre-shared key is a pass-phrase—a sequence of 8–63 ASCII-encoded characters.
Wi-Fi Protected Access 2 (WPA2)
WPA2 is based on the ratified version of the IEEE 802.11i standard. This makes it quite
different from plain WPA, which was a stop-gap measure based on draft versions of the
IEEE 802.11i standard. WPA2 is the Wi-Fi Alliance’s moniker for its implementation of
the final IEEE 802.11i standard.
Key Management
The keys are the jewels in any crypto system because they are used in the
encryption and decryption process. Key management, an important aspect of any
cryptographic system, includes the following:
■■ A mechanism to protect the keys
■■ A mechanism for the communicating parties to use in agreeing on the
secret keys to use
■■ A mechanism for ensuring that unauthorized parties cannot use the keys
■■ A mechanism for ensuring that the keys are used for their intended
purpose
■■ A secure method for distributing or transporting the secret keys to the
parties that need them
■■ Automatic and periodic generation of new keys

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WPA2 has several components, discussed in the following sections, that can work
individually or collectively to provide what the IEEE 802.11i subcommittee calls a
“robust security network.”
CCMP/AES
CCMP is an awkward mouthful of an acronym that stands for Counter Mode with
Cipher Block Chaining Message Authentication. CCMP provides authentication,
confidentiality, and integrity checking services to any cryptographic system in which
it is used. Under the hood of CCMP is the AES algorithm.
Let’s try to break down CCMP into its individual parts to simplify and explain it.
Recall that counter mode (CM) is one of the modes in which block ciphers can operate.
You might also recall the cipher-block chaining (CBC) mode, another popular mode for
block ciphers. This leaves us with the Message Authentication Code component of the
name. We haven’t talked about this yet so I’ll briefly introduce it and its associated
concepts next.
Hash Functions
Hash functions, or algorithms, are used for detecting unauthorized modifications to
data. They serve as a type of watermark or digital signature that can be applied to data.
A popular example of a hash function is a one-way hash, in which a sending entity
takes any arbitrary data, runs it through the hash function, and produces a fixed-
length value called the hash. The resulting hash value is appended to the data and sent
to the receiving entity. The receiver gets the data with the appended hash, runs the
same hashing function on the data component, and compares the result with the hash
value that was sent with the original data. If the two values are different, the receiver
can conclude that the data may have been altered along the way. But if the two values
are the same, the receiver can reasonably conclude that the integrity of the data has
been preserved. The one-way hash function does not use any keys and is not used for
encryption in any way.
Note  The process of applying the hash function is sometimes called digesting, and the result is
sometimes called a message digest.
Message authentication is a method used in cryptosystems for verifying the
authenticity and integrity of data. The integrity aspects of message authentication are
concerned with making sure that data is not modified or altered in any way before
reaching its intended recipient. And the authenticity aspect is concerned with making
sure that the data originates from the entity that receiver is expecting it to originate
from. It is also referred to as message integrity code and message authentication code.
Currently two approaches are used to ensure integrity and authenticity: Hash-based
Message Authentication Code (HMAC) and Cipher Block Chaining Message
Authentication Code (CBC-MAC).

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HMAC  HMAC combines the process of hash functions with a Message Authentication
Code function of some sort. One key difference between plain hash functions and the
HMAC function is the use of a secret key. The key type used here is symmetric. The
HMAC process works like this:
1. The sender and the receiver entities agree on a secret key to be used.
2. The sender decides to transmit some arbitrary data to a receiver. But the sender
wants to make sure that data is received intact at the other end and wants to
provide some guarantee to the receiver that the sender actually sent the data.
3. The sender appends the agreed upon secret key to the data to be sent.
4. The result is passed through a hash function. The new hash value is the
message authentication code.
5. The message authentication code is appended to the original data (plain-text)
and sent to the receiver.
6. The next steps are carried out at the receiver end.
7. The receiver receives the data with the appended message authentication code.
8. The receiver appends the shared secret key to the data. The result is run
through a hash function again. The hash value is the receiver’s version of the
message authentication code.
9. The receiver compares his/her value of the message authentication code with
the value that was received with the message from the sender.
10. If the computed value is the same as the received value, the data can be
assumed to have passed the integrity and authentication test.
11. If the computed value is different from the received value, it can be assumed
that the data was tampered with along the way.
Note that nowhere in the process is the data encrypted. Encryption or confidentiality
is not a function of HMAC.
CBC-MAC  CBC-MAC is a combination of the CBC mode used in block ciphers and a
message authentication code of some sort.
CBC-MAC works in a simple but elegant way, described as follows:
1. The sender and the receiver entities agree on a secret key to be used.
2. The sender decides to transmit some arbitrary data to a receiver. But the sender
wants to make sure that data is received intact at the other end and also wants
to provide some guarantee to the receiver that the sender actually sent the data.
3. The sender encrypts the arbitrary plain-text data using the CBC symmetric
block cipher mode of operation. The encryption will be done on blocks of the
plain-text and will result in corresponding blocks of cipher-text.

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4. The output of the final block of cipher-text is used as the message
authentication code, which is appended to the plain-text data.
5. The sender sends the plain-text and message authentication code combination
to the receiver.
6. The next steps are carried out at the receiver end.
7. The receiver encrypts the plain-text data with the shared secret key. The
encryption is performed with the CBC symmetric block cipher again, resulting
in blocks of cipher-text.
8. The last block of cipher-text is used as the receiver-generated message
authentication code value.
9. The receiver compares the message authentication code value with the value
that was received with the message from the sender.
10. If the computed value is the same as the received value, the data can be
assumed to have passed the integrity and authentication test.
11. If the computed value is different from the received value, it can be assumed
that the data was tampered with along the way.
Note that nowhere in the process is the hashing algorithm performed. This is the
key distinguishing factor between HMAC and CBC-MAC. You should also note that
the whole point of the CBC-MAC process is not to hide the plain-text data.
EAP
The Extensible Authentication Protocol (EAP) is an authentication framework that
forms a basis upon which other authentication schemes rest. It forms a big part of the
ratified IEEE 802.11i standard.
As indicated by its name, the EAP framework was designed with extensibility and
authentication in mind. For the authentication component, various credentials such as
usernames, passphrases, digital certificates, smart cards, and one-time passwords are
acceptable.
The extensibility component of EAP implies several things as follows:
■■ Arbitrary authentication mechanisms can be designed around it.
■■ The base EAP specification can be kept simple and lightweight.
■■ Advanced features and their resulting complexity can be abstracted away from
EAP and implemented in the solutions that use EAP.
■■ EAP is relatively future-proof. As technology advances and new demands
are placed on existing solutions, EAP can easily adapt to accommodate these
changes.

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EAP can be encapsulated inside any Data Link layer protocol such as Ethernet,
Point-Point-Protocol (PPP), IEEE 802.11 frames, and so on.
EAP Entities
Entities are the network components that use EAP to meet their authentication and key
management needs in a wireless network. Notice the close semblance and verbiage to
the components in the RADIUS world (see Chapter 10) or the IEEE 802.1X world. The
entities in any EAP scheme may include any of the following components:
■■ Peer  The device or the user that wants to access the protected network
resources. In a wireless network environment, the peer is often the wireless
STA, the entity that responds to the authenticator. In the IEEE-802.1X world,
this component is also known as the supplicant.
■■ Authenticator  The gatekeeper entity that initiates the EAP authentication
conversation with the back-end components. In a wireless network
environment, this could be a wireless access point (WAP). In the RADIUS
world, it is called the network access server (NAS).
■■ Backend authentication server  The authenticator relies on the back-end
authentication server to provide authentication services. This component
executes EAP methods or grammar on behalf of the authenticator.
■■ EAP server  The component that terminates the EAP conversation with the
peer component. This component or functionality is often discretely packaged
with the back-end authentication component. When combined in this way, the
service they provide is similar to the service provided by the access server in
the RADIUS world.
The back-end authentication server and the EAP server possess the final knowledge
of who should have access to what and when.
EAP Grammar
EAP grammar refers to the way EAP is spoken among the components that want to use
the authentication and key management services provided by EAP. EAP’s grammar is
quite simple and consists of the following four primitives:
■■ Request  The authenticator sends these types of packets to the supplicant.
■■ Response  The supplicant sends these types of packets to the authenticator.
■■ Success  These are used to indicate successful authentication.
■■ Failure  These are used to indicate an unsuccessful authentication.

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EAP Types
Different implementations of the EAP framework exist to address the issues of
authentication and key exchange. Note that the EAP framework is concerned not only
with securing wireless communications but also with wired communications. The
following sections discuss some EAP implementations that are especially popular in
the wireless world.
EAP-TLS
The EAP-Transport Layer Security (EAP-TLS) authentication protocol was developed
by Microsoft and is fully described in the IETF’s RFC 5216. It uses the facilities
provided in the traditional standalone TLS protocol.
EAP-TLS relies on the use of digital certificates to authenticate the parties that want
to communicate with one another. It requires that the entities that want to use EAP
for authentication and key management mutually authenticate each other. This means
that the entities participating in the EAP-TLS conversation require their own digital
certificates. In environments where digital certificates are not already widely in use,
this requirement may add an extra burden for the wireless network administrator.
EAP-TLS Conversation  A successful EAP-TLS conversation between EAP entities is
outlined in the following steps. The entities are the peer (such as a wireless client STA),
the authenticator (such as a WAP), and the EAP server/back-end authentication server
(such as a RADIUS server).
1. The parties that want to be authenticated—the peer and the authenticator—
agree to do so via EAP.
2. The authenticator asks the peer to identify itself via an EAP-Request message.
3. The peer sends its identity to the authenticator via an EAP-Response message.
4. From this point on, the EAP-TLS conversation appears to happen between the
peer and the authenticator. But in reality, the authenticator component is acting
as a go-between, by conveying the messages between the peer and the EAP
server/back-end authentication server components.
5. After receiving the peer’s identity, the EAP server sends (via the authenticator)
an EAP-Request message with the EAP-Type set to EAP-TLS. This message
serves as a way of telling the peer that the EAP-TLS conversation is about to
begin.
6. The peer responds with an EAP-Response packet with the EAP-Type set to
EAP-TLS. The packet will serve as a way for the peer to agree to start EAP-TLS
via a client_hello message.
7. The EAP server responds to the peer with an EAP-Request packet with the
EAP-Type set to EAP-TLS. The packet contains information such as the server
TLS certificate and the server_hello message. The server will also request the
peer to send its own certificate.

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8. The peer responds with an EAP-Response packet with the EAP-Type set to
EAP-TLS. The packet contains information such as the peer’s TLS certificate
and so on.
9. The EAP server verifies the peer’s certificate and digital signature. The peer
does the same thing.
10. If everything checks out from the server’s perspective, the EAP server sends an
EAP-Success packet.
11. If the peer fails to authenticate itself successfully to the EAP server, the server
sends an EAP-Failure message.
EAP-TTLS
The EAP-Tunneled Transport Layer Security (EAP-TTLS) protocol is an extension of the
EAP-TLS mechanism that is described in the IETF’s RFC 5281.
EAP-TTLS is different from EAP-TLS because it does away with the EAP-TLS
requirement of a supplicant-side certificate. Only the authentication server component
requires a digital certificate.
The authentication server is authenticated using its digital certificate. An encrypted
tunnel is then established between the peer (or supplicant) and the authentication
server. The peer’s authentication credentials, such as a digital certificate or password,
are passed to the authentication server over the established tunnel. The peer can use
other authentication methods such as Challenge-Handshake Authentication Protocol
(CHAP), Password Authentication Protocol (PAP), and Microsoft CHAP (MS-CHAP)
v2. These alternatives were discussed in Chapter 10.
Having to manage certificates only on the server side makes EAP-TTLS much easier
to manage, because the wireless administrator does not have to worry about creating
and managing digital certificates on all the wireless client STAs.
EAP-PSK
The EAP Pre-Shared Key authentication protocol, like the other EAP types discussed
thus far, can be used for providing authentication services to entities in a wireless
network. It is described in the IETF document RFC 4764.
The Pre-Shared Key refers to a key or secret that needs to be derived and shared
by the parties by some mechanism before the EAP-PSK conversation takes place. The
security provided by EAP-PSK will be compromised if this secret key is exposed.
Note that EAP-PSK is different from the Pre-shared Key authentication mode used
in Wi-Fi Protected Access (WPA). The WPA implementation is commonly known as
WPA-PSK.
EAP-PSK is a simpler in its design and in the way it functions when compared
to EAP-TLS or EAP-TTLS. This simplicity is due to the fact that it does not use
asymmetric cryptography as the other two do. This same simplicity also means that
EAP-PSK cannot offer some of the advanced security features of the others.
Under the hood, EAP-PSK uses the AES symmetric block cipher.

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EAP-SIM
This EAP authentication type uses the Subscriber Identity Module (SIM) used on
Global System for Mobile (GSM) communications mobile networks. GSM is a second-
generation mobile network standard. (See Chapter 7 for more on GSM.) The SIM card,
as it is fondly called, is a type of smart card that is distributed by the mobile network
operators to their subscribers.
EAP-SIM was developed by the Third Generation Partnership Project (3GPP). The
IETF document RFC 4186 describes EAP-SIM.
EAP-SIM builds on and extends the traditional GSM security mechanisms. It extends
normal GSM authentication by providing a mechanism for the parties to authenticate
each other mutually.
EAP-AKA
The EAP-Authentication and Key Agreement (AKA) protocol is used in third-generation
(3G) mobile networks. Universal Mobile Telecommunications System (UMTS) and
CDMA2000 are regarded as 3G mobile technology standards.
EAP-AKA can be used for authentication purposes along with 3G identity modules
and network infrastructures.
EAP-AKA was developed by 3GPP. The IETF document RFC 4187 describes EAP-AKA.
In general, EAP-AKA provides more advanced security mechanism compared to
EAP-SIM.
Note  It is possible to use EAS-SIM or EAS-AKA to authenticate to noncellular networks such as
wireless local area networks (WLANs).
  All that is needed is to configure the authenticator (WAP) to send authentication requests to back-
end authentication servers or the EAP server of a cellular network provider.
  For example, the owner (the supplicant) of a GSM phone could use her credentials, which are
stored on her SIM card, to hop onto a foreign WLAN. As long as the WLAN is preconfigured for
this, the cellular network provider will bill the user on behalf of the WLAN operator for the use of the
high-speed WLAN network. The user gets the benefits of using the faster WLAN resources for her
data transfers (or even voice over IP calls) instead of using the more expensive provider cellular
network. The role of the cellular service provider in this case is relegated to mere authentication and
accounting functions.
IEEE 802.11i
This chapter has been building toward this discussion—almost everything discussed so
far will help you understand the why and the how behind IEEE 802.11i.
The why was answered in the discussion about WEP and WPA. WEP was one of
the earlier attempts at providing some kind of security for wireless communications.

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In due time, several vulnerabilities were discovered in WEP that made it no longer
suitable. However, WEP was so widely engrained in so many wireless network
security solutions that great care had to be taken to provide an alternative for it. This
was especially important because proposed alternatives had to work with existing
and widely deployed wireless hardware. The stop-gap solution was WPA, and the
requirements for WPA were designed such that existing equipment that use WEP could
be easily upgraded to support WPA via software or firmware updates. Eventually,
WPA2 was finalized and was a big part of the IEEE 802.11i picture.
The how behind IEEE 802.11i is in all the pieces that work together to offer a long-
term authentication, confidentiality, and integrity as a security solution for wireless
networks. Some of the pieces are 802.1X/EAP, which is used for authentication, and the
AES-CCMP, which is used for satisfying the integrity and confidentiality needs.
Four-Way Handshake
An important aspect of the different EAP types was to provide a secure means of
authenticating the parties that wanted to communicate. Another important by-product
of the EAP is to generate symmetric keys, such as the Master Session Key (MSK)—an
all-important key.
After the authentication stage has been successfully completed, next comes the
four-way handshake, an Authentication and Key Management Protocol (AKMP) used
in IEEE 802.11i. Its job is to confirm that the parties that want to communicate securely
each possess the Pairwise Master Key (PMK) and to also distribute the group keys. The
PMK is derived from the MSK.
In general, the so-called master keys are not themselves used for encrypting data.
They are used for generating other subordinate and temporary keys that can be used
for encrypting data.
The four-way handshake is used for generating dynamic keys that will be used
for protecting subsequent data transmissions. These keys are transient or temporary
by nature and as such are referred to as transient keys and temporal keys. The two types
of transient keys that can be derived from the four-way handshake are the Pairwise
Transient Key (PTK) and the Group Temporal Key (GTK).
In general, the pairwise keys are used only between a pair of communicating
entities. The group keys can be used between two or more communicating entities.
IEEE 802.11i Considerations
With all the terms and concepts used in this chapter, you may not be immediately clear
about what exactly you, as a wireless network administrator, need to do to deploy a
network that is IEEE 802.11i compliant. Table 11-2 presents that information in bite-
sized pieces.

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Scenario
Suggested Solutions and Tips
You manage a small wireless
network with only a few users
and devices and need to use
the most current security
mechanisms.
Consider IEEE 802.11i.
Use IEEE 802.11i with pre-shared keys, which
help you avoid the additional overhead of
maintaining a public key infrastructure (PKI).
You manage a large to medium-
sized wireless network and need
to use the most current security
mechanisms.
Consider IEEE 802.11i.
Consider using IEEE 802.11i with one of the EAP
authentication types.
You already use digital certificates Consider using EAP-TTLS with IEEE 802.11i.
for server- or infrastructure-side
authentication on your network.
EAP-TTLS does not require mutual
authentication.
You already use digital certificates
for server- or infrastructure-side
authentication and for client-side
authentication on your network.
Consider using EAP-TLS with IEEE 802.11i.
EAP-TLS requires mutual authentication.
You are considering using
EAP-TLS or EAP-TTLS on the
infrastructure side of your
wireless network.
You need a RADIUS server implementation that
supports EAP.
You need a PKI that lets you manage the digital
certificates that will be used, which includes the
tasks of issuing, revoking, signing, and storing
the certificates. Some of this can occur via a
certificate authority implementation.
Your WAPs (the authenticator entity) must
support 802.1X so that they can communicate
with the RADIUS servers via EAP.
You might get 802.1X support in infrastructure
hardware via simple firmware upgrades if the
vendor doesn’t support it.
Consider temporarily allowing legacy
authentication mechanism to coexist with new
802.1X-based mechanisms, which will help if
things don’t work as smoothly as planned.
You are considering using EAP-
TLS or EAP-TTLS on the client or
peer side of the wireless network.
You need the wireless clients STAs to be able to
talk 802.1X to the access point. The supplicant
software on the clients needs to support the EAP
type with which the server is configured.
Table 11-2.  IEEE 802.11i Wireless Network Deployment Considerations

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Summary
This was a tough chapter to write and probably a tough read, too. Weaving all the
sometimes disparate topics together to try to build one simple idea is a difficult task.
Cryptography is not for the faint of heart; nor is it an easy subject. Its beauty lies in
the fact that it is guided by simple core principles, which have remained unchanged for
centuries, and they are mostly common sense principles.
You learned that any good cryptosystem should provide authentication,
confidentiality, and integrity.
The methods (or algorithms) that have been developed to provide or support these
objectives were discussed. We started by looking at some generic algorithm/ciphers
that form the bedrock of modern-day cryptographic systems.
We moved on to practical applications of the low-level concepts and algorithms
that have been reused in developing standards and protocols for protecting wireless
networks. We glued all the theoretical aspects together with the practical aspects of
administering a secure wireless network.
After all has been said and done, remember that in matters of secrecy, “Three may
keep a secret, if two of them are dead.”

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Part V
Wireless Devices
Configuration and
Other Wireless Network
Considerations

21 Pages 201-210

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Chapter 12
Infrastructure Device
Configuration
179

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Wireless Network Administration: A Beginner’s Guide
Key Skills and Concepts
■■ Understand the key infrastructure components of a wireless network.
■■ Understand the functions and roles of components of a wireless network.
■■ Design a simple wireless local area network (WLAN).
■■ Configure a generic wireless access point (WAP) device.
■■ Configure a generic WLAN controller device.
In this chapter, we begin building a simple wireless network that will incorporate
some of the elements and technologies discussed in the preceding chapters.
Our sample network will comprise infrastructure-side devices and client-side devices.
The infrastructure component of our network will include the following:
■■ A standalone WAP
■■ A WLAN controller
■■ Managed WAPs
And the following devices make up the client components:
■■ Windows-based client devices
■■ Macintosh-based client devices
■■ Linux-based client devices
We will take a four-step approach to building this heterogeneous network:
1. Set up the infrastructure side devices in this chapter.
2. Set up the Windows-based client device in Chapter 13.
3. Set up the Macintosh-based client device in Chapter 14.
4. Set up the Linux-based client device in Chapter 15.
We will build our network to conform to the network diagram shown in Figure 12-1.
We’ll begin building our infrastructure network by identifying the types and
roles of the individual devices that make up the network. Then we’ll walk through
configuring the devices.
Note  Throughout this part of the book, the configuration process has been kept as generic as
possible so that you can use the knowledge gained here to configure other real-world infrastructure
devices. The basic principles and concepts guiding the functioning and configuration of wireless
networking gear are similar; what differs sometimes is the terminology and user interfaces that the
equipment manufacturers use in their products.

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Managed Access Point
Host name: wap-2
SSID: area-2
VLAN IP: 192.168.2.254
IEEE Standard: 802.11 b, g, a, n
Managed Access Point
Host name: wap-1
SSID: area-1
VLAN IP: 172.16.1.254
IEEE Standard: 802.11 b, g, a, n
Standalone Wireless Access Point
Host name: wap-3
SSID: area-3
LAN IP: 192.168.3.1
WAN IP: 10.3.3.2
IEEE Standard: 802.11 b, g, a, n
Router/Gateway
LAN0 IP Address: 10.3.3.1
Router/Gateway
LAN1 IP Address: 10.0.0.1
Router/Gateway
WAN IP Address: 1.1.1.1
Internet
Wireless LAN Controller
Host name: controller01
IEEE Standard: 802.11 a, b, g, n
SSID: area-1, area-2
WAN IP Address: 10.0.0.2
Management IP: 192.168.0.1
Figure 12-1.  Network diagram
The Wireless Access Point
The network WAP in our sample network functions in standalone mode, which means
that it is not being managed by a central controller. It does not take its configuration
information from any other device; all configuration is performed directly on the
device by the wireless network administrator.
The WAP in our network is the award-winning model nix-WAP-2012 (a fictitious
product) made by Caffenix, with the following outstanding features:
■■ Rugged and works under extreme conditions.
■■ Easy to configure.
■■ Standards-based.
■■ It’s free.
The specifications of the nix-WAP-2012 and our configuration objectives are shown
in Table 12-1.

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Specification
Host name
SSID
Supported ciphers and
authentication
Encryption key or passphrase
Wireless PHYs supported
Physical ports
Wireless interface
Value
wap-3
area-3
WEP 64 / 128 bits
WPA-Personal / TKIP
WPA-Personal / CCMP
WPA-Enterprise / TKIP
WPA2-Personal / TKIP
WPA2-Personal / CCMP
WPA2-Enterprise / CCM
never-never-land
802.11b, 802.11g, 802.11a, 802.11n
1 10/100 Mbit/s Ethernet port (WAN port)
4 Gigabit Ethernet ports (LAN switch ports)
1 wireless interface
Table 12-1.  Specifications of the nix-WAP-2012
Configuring the WAP
We start by using a separate computer to configure the WAP. We use an Ethernet cable
to connect the computer’s Ethernet port to any of the local area network (LAN) ports
of the WAP. By default, the WAP automatically assigns an IP address to any system
plugged into any of its LAN ports.
We log into the management interface of the WAP using a web browser. Out of the
box, the WAP has a factory-assigned IP address of 192.168.3.1, and it also has a factory-
assigned administrative username of “administrator” and a very insecure password of
“password.”
After we log in, the nix-WAP-2012 prompts us to launch the initial configuration
wizard. The entire configuration process for the WAP is separated into three areas. The
wizard also separates the configuration tasks along these three categories:
■■ Global Configuration
■■ Network Configuration
■■ Wireless and Security Configuration
The wizard uses a question-and-answer approach to make the initial configuration of
the unit as easy as possible. It asks questions and uses your answers to set the configuration
parameters. Some of the questions are helpfully interspersed with explanations.

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The following sections walk through the process and options selected while we use
the wizard.
Global Configuration of the nix-WAP-2012
The wizard starts with the global configuration tasks.
1. Select the option to start the configuration wizard for the AP.
2. Create a host name or system name for the WAP. Type the host name shown
here and then press enter.
> wap-3
3. Change the default factory-assigned administrative password for the WAP.
Type this new password:
> caffenix-wap3-pw
4. Would you like to save the changes to the global configuration section?
The options are {YES} {NO}
> YES
Caution  It is very important that you always change the passwords for all networking equipment
from the default factory-assigned values when initially configuring such devices. Not doing so can
have serious security consequences.
Network Configuration of the nix-WAP-2012
The network configuration section of the wizard setup is where Internet Protocol (IP)
addresses are assigned to the ports and interfaces on the unit. The gateway, Dynamic
Host Configuration Protocol (DHCP), and Domain Name System (DNS) values are
also set.
Figure 12-2 shows an exploded view of the interfaces available on the nix-WAP-
2012 and the network addresses that will be assigned to the interfaces when we are
done.
The wizard continues to the Network Configuration tasks:
1. How will the WAN port be configured?
The options are {static IP} {Automatic – DHCP} {PPPOE}
> static IP
2. What is the IP address and network mask for the WAN interface? Press enter
when done.
Hint: The accepted format is xxx.xxx.xxx.xxx / xxx.xxx.xxx.xxx
> 10.3.3.2 / 255.255.255.252

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LAN Interface: lan0
IP: 192.168.3.1
Netmask: 255.255.255.0
Services: DHCP Server
DHCP Scope: 192.168.3.101-120
Wireless Interface: wifi0
Switch Interface
4 × Gigabit Ethernet Ports
Standalone Wireless Access Point
Manufacturer: Caffenix Corp.
Model: nix-WAP-2012
Host name: wap-3
SSID: area-3
Wireless PHYs: 802.11 b, g, a, n
WAN Port: wan0
IP: 10.3.3.2
Netmask: 255.255.255.252
Gateway: 10.3.3.1
Internet
Figure 12-2.  Exploded view of interfaces and network addresses
3. Enter the default remote gateway (or router) IP address. Press enter when done.
Hint: The accepted format is xxx.xxx.xxx.xxx / xxx.xxx.xxx.xxx
> 10.3.3.1 / 255.255.255.252
4. Enter the remote DNS server IP address for this WAP. Press enter when done.
Hint: The accepted format is xxx.xxx.xxx.xxx / xxx.xxx.xxx.xxx
> 10.3.3.1 / 255.255.255.252
5. Enter the IP address and network mask for the LAN interface. Press enter
when done.
Hints: The wireless interface (wifi0) is bridged or wired internally to the four
LAN switch ports to form a single virtual interface. This new virtual interface
is called the LAN interface of the access point (AP) and is treated as such. This
combined interface name is lan0.
The accepted format is xxx.xxx.xxx.xxx / xxx.xxx.xxx.xxx
> 192.168.3.1 / 255.255.255.0

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6. Do you want this device to automatically assign IP addresses to clients
connected to its wireless and Ethernet interfaces?
The options are {YES} {NO}
Hint: Answering YES here will turn on the DHCP server service on the AP. To
avoid conflicts on any other directly connected networks, make sure that only
one DHCP server is running on any network segment.
> YES
7. By default, the DHCP server you have just enabled can assign 255 unique IP
addresses to DHCP clients. You can change this default value by supplying a
lower range. Would you like to change the default DHCP range?
The options are {YES} {NO}
Hint: This DHCP range is also known as the DHCP scope.
> YES
8. Enter the new DHCP starting address range. Press enter when done.
Hints: The starting range is the lower boundary of the DHCP scope or the
smallest IP address in the scope.
The accepted format is xxx.xxx.xxx.xxx
> 192.168.3.101
9. Enter the new DHCP ending address range. Press enter when done.
Hints: The ending range is the upper boundary of the DHCP scope Or the
highest IP address in the scope.
The accepted format is xxx.xxx.xxx.xxx
> 192.168.3.120
10. Your DHCP server will be able to supply 20 DHCP clients at a time with IP
configuration information. Is this OK? Press enter when done.
The options are {YES} {NO}
> YES
11. Would you like to save the changes to the Network Configuration section?
The options are {YES} {NO}
> YES
Wireless and Security Configuration of the nix-WAP-2012
The wireless and security configuration section of the WAP wizard setup controls the
radio frequency (RF) properties of the unit. The WAP itself should, of course, have the
built-in hardware to support the different PHY technologies that we will be configuring.

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The wizard continues to the Wireless Configuration tasks:
1. This WAP has built-in wireless radios that can support the following wireless
technologies: 802.11b, g, a, n. Which of the wireless technologies would you
like to enable? Press enter when done.
The options are {802.11b} {802.11g} {802.11a} {802.11n}
Hint: You should enable support only for the technologies that you use.
> 802.11n
2. Create a network name (SSID) for the wireless network.
> area-3
3. Would you like to secure communication for the wireless network?
The options are {YES} {NO}
> YES
4. There are several authentication and encryption methods that can be used to
secure the wireless network. Which of these would you like to use?
The options are {WEP 64 bits} {WEP 128 Bits} {WPA-Personal/TKIP}
Hint: Make sure that whatever option you select is also supported by the
wireless clients.
> WPA-Personal/TKIP
5. Please create a secret key that will be used in encrypting and decrypting the
communications. Press enter when done.
Hint: The secret key is the passphrase. A good passphrase should be a random
alphanumeric string at least eight characters long.
> never-never-land
6. Would you like to save the changes to the network configuration section?
The options are {YES} {NO}
> YES
The WLAN Controller
The second major device in our infrastructure arsenal is the WLAN controller, which
can be used to manage various aspects of the APs that it controls. For example, the
controller can be used to perform configuration, firmware, radio resource management,
auditing, and security functions of the APs connected to it.

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Our WLAN controller of choice is the award-winning model nix-WLC-2012 made
by Caffenix. The nix-WLC-2012 has won many industry awards and is the best in its
class. Following are the highlights of the unit:
■■ Rugged and works under extreme conditions
■■ Modular
■■ Easy to configure
■■ Standards-based
■■ It’s free
The capabilities and specifications of the nix-WLC-2012 are shown in Table 12-2,
which also shows our configuration objectives.
Configuring the WLAN Controller
We will use a separate computer to configure the controller. We will connect the
Ethernet port of the computer to the management port of the controller using an
Ethernet cable. The controller will automatically assign an IP address to any system
connected to its management port.
We log into the management interface of the WLAN controller using a web
browser. Out of the box, the management interface has a factory-assigned IP address
of 192.168.0.1. The controller also has a factory-assigned administrative username of
“administrator” and a very insecure password of “password.”
Specification
Value
Host name
controller01
Supported ciphers and authentication WEP 64 / 128 bits
WPA-Personal / TKIP
WPA-Personal / CCMP
WPA-Enterprise / TKIP
WPA2-Personal / TKIP
WPA2-Personal / CCMP
WPA2-Enterprise / CCMP
Physical ports
1 Gigabit Ethernet
1 management port
Virtual/logical interfaces supported 1–100
Wireless PHYs supported
802.11b, 802.11g, 802.11a, 802.11n,
Bluetooth, ZigBee, RFID, GSM, CDMA
Table 12-2.  WLAN Controller Specifications

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After we log in, the controller will prompt us to launch the initial configuration
wizard. The entire configuration process for the controller is separated into five areas.
The wizard also separates the configuration tasks along these five areas:
■■ Global Configuration
■■ Network Configuration
■■ Wireless Configuration
■■ Virtual Local Area Network (VLAN) Configuration
■■ VLAN Security Configuration
The wizard uses a question-and-answer approach to make the initial configuration
of the unit as easy as possible. It asks the questions and uses the answers supplied
by the user to set the configuration parameters. Some of the questions are helpfully
interspersed with explanations called hints.
Global Configuration for nix-WLC-2012
The following steps walk through the process and options selected while using the
wizard. The wizard starts off with the global configuration tasks.
1. Select the option to start the configuration wizard for the controller.
2. We need to create a host name or system name for the controller. Type the host
name shown here when prompted by the wizard:
> controller01
3. Create a user account that will be used to manage the controller. Type this
username when prompted:
> admin
4. We need to change the default factory-assigned administrative password for
the controller. Changing the controller’s administrative password will also
automatically update the administrative passwords of all the devices that are
managed by this controller. Type this password when prompted by the wizard:
> caffenix-controller-pw
5. Would you like to save the changes to the global configuration section?
The options are {YES} {NO}
> YES
Network Configuration for the nix-WLC-2012
The Network Configuration section of the setup wizard deals with the networking
properties of physical interfaces or ports on the nix-WLC-2012. This is where IP
addresses are assigned to the ports and interfaces on the unit. This is also where the
gateway, DHCP, and DNS values are set.

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The settings here affect how the controller connects to the wired network
segment, and this, by extension, affects how the remotely managed APs reach the
wired segment, too.
Figure 12-3 shows an exploded view of the physical and logical interfaces available
on the nix-WLC-2012 and the network addresses that will be assigned to the interfaces
when we are done.
The wizard continues to the Network Configuration tasks:
1. How will the WAN port be configured?
Hint: The WAN port is used for connecting the controller to other wired
networks.
The options are {static IP} {Automatic – DHCP}
> static IP
Managed Access Point
Host name: wap-2
MAC Address: 12-34-56-78-9A-BC
VLAN IP: 192.168.2.254
Wireless PHYs: 802.11 b, g, a, n
Managed Access Point
Host name: wap-1
MAC Address: 12-34-56-78-9B-CD
VLAN IP: 172.16.1.254
Wireless PHYs: 802.11 b, g, a, n
area-2
area-1
vlan2
vlan1
WAN Interface
IP: 10.0.0.2
Gateway/DNS server
IP: 10.0.0.1
Management port
IP: 192.168.0.1
Wireless LAN Controller
Manufacturer: Caffenix Corp.
Model: nix-WLC-2012
Host name: controller01
IEEE Standard: 802.11 a, b, g, n
SSID: area-1, area-2
WAN IP Address: 10.0.0.2
Management Interface IP: 192.168.0.1
Wireless PHYs: 802.11b, 802.11g,
802.11a, 802.11n, Bluetooth,
ZigBee, RFID, GSM, CDMA
Figure 12-3.  Exploded view of the physical and logical interfaces available on the nix-WLC-2012

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2. What is the IP address and network mask for the WAN interface? Press enter
when done.
Hint: The accepted format is xxx.xxx.xxx.xxx / xxx.xxx.xxx.xxx
> 10.0.0.2 / 255.255.255.252
3. Enter the default gateway IP address for the controller. Press enter when done.
Hint: The accepted format is xxx.xxx.xxx.xxx / xxx.xxx.xxx.xxx
> 10.0.0.1 / 255.255.255.0
4. Enter the DNS server IP address for the controller. Press enter when done.
Hint: The accepted format is xxx.xxx.xxx.xxx / xxx.xxx.xxx.xxx
> 10.0.0.1 / 255.255.255.0
5. Would you like to save the changes to the network configuration section?
The options are {YES} {NO}
> YES
Wireless Configuration for the nix-WLC-2012
The Wireless Configuration section of the controller wizard setup controls the RF
properties of the controller. The controller itself should, of course, have the proper
hardware built in to support the different PHY technologies. If, for example the controller
needs to manage an AP that supports only the IEEE 802.11n standard, the controller itself
needs to have a built-in radio that can transmit and receive using IEEE 802.11n.
The wizard continues to the Wireless Configuration tasks:
1. This controller has built-in wireless radios that can support the following
wireless technologies: 802.11b, 802.11g, 802.11a, 802.11n, Bluetooth, ZigBee,
RFID. These are also the allowed options.
Which of the wireless technologies would you like to enable? Press enter when
done.
Hint: You should enable support only for the technologies that you use.
The options are {802.11b} {802.11g} {802.11a} {802.11n} {blue} {zee} {rfid}
> 802.11b 802.11g 802.11a 802.11n
2. This controller has internal antennas as well as support for external antennas.
Will there be any external antenna attached to the unit?
The options are {YES} {NO}
> YES
3. Would you like to save the changes to the Wireless Configuration section?
The options are {YES} {NO}
> YES

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Virtual Local Area Network (VLAN) Configuration for the nix-WLC-2012
A VLAN in our wireless controller terminology is like a virtual interface that is used
for communicating with a particular WAP that is to be managed by the controller. Our
sample wireless LAN controller can support up to 100 different VLANS.
Each VLAN is in its own little world, and the default behavior of the controller is to
disable all communication between different VLANs on the controller. Permissions must be
explicitly granted for any communication to take place between all the APs on a controller.
The virtual interface associated with each VLAN is named vlanx, where x is a number
corresponding to the virtual interface. So, for example, for the first VLAN to be created,
the interface will be named vlan1, and the second will be named vlan2, and so on.
The Media Access Control (MAC) address of the managed AP is used as a unique
identifier when associating the AP with the VLAN defined on the controller.
With this background information we can now continue with the configuration of
the controller.
1. Type the number of access points that this controller will manage now. Press
enter when done.
The options are {1} {2} {3} {4}...{100}
>2
2. Type the name of the VLANs to be associated with each access point. Press
enter when done.
The options are {vlan1} {vlan2} {vlan3} {vlan4}...{vlan100}
> vlan1 vlan2
3. Enter the MAC address of the access point to be associated with vlan1. Press
enter when done.
> 12-34-56-78-9A-BC
4. Enter the MAC address of the access point to be associated with vlan2. Press
enter when done.
> 12-34-56-78-9B-CD
5. Would you like to configure vlan1 now? Press enter when done.
The options are {YES} {NO}
> YES
6. Enter the SSID to be associated with vlan1. Press enter when done.
> area-1
7. A logical interface has to be created for the remote access point connected to
vlan1. The interface name will be vlan1.1. Specify an IP address and subnet
mask for the interface for the remote AP (vlan1.1). Press enter when done.

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Hint: The accepted format is xxx.xxx.xxx.xxx / xxx.xxx.xxx.xxx
> 172.16.1.254 / 255.255.255.0
8. Are you ready to save and apply the configuration for vlan1? Answering YES
will push the configuration settings to the managed wireless access point. Press
enter when done.
The options are {YES} {NO}
> YES
9. Would you like to configure vlan2 now?
The options are {YES} {NO}
> YES
10. Enter the SSID to be associated with vlan2. Press enter when done.
> area-2
11. A logical interface has to be created for the remote access point connected to
vlan2. The interface name will be vlan2.1. Specify an IP address and subnet
mask for the interface for the remote AP (vlan2.1).
Hint: The accepted format is xxx.xxx.xxx.xxx / xxx.xxx.xxx.xxx
> 192.168.2.254 / 255.255.255.0
13. Are you ready to save and apply the configuration for vlan2? Answering YES
will push the configuration settings to the managed wireless access point.
The options are {YES} {NO}
> YES
Control and Provisioning of Wireless Access Point Protocol
Our fictitious wireless LAN controller uses an oversimplified mechanism to find
and establish initial communications with the WAPs.
The Control And Provisioning of Wireless Access Points (CAPWAP) protocol
is an example of a real-world method (protocol) that does the same thing and
much more. It is based on an IETF specification described in RFC 5414.
CAPWAP is an interoperable protocol that enables an access controller to
manage, control, and provision a collection of wireless STAs (such as APs). It
simplifies the deployment and management of wireless networks.
CAPWAP uses a simple mechanism to perform its functions. The WAPs that
need to be managed send a discovery “Request” message. The controller responds
with a discovery “Response” message. After this initial set of messages is sent
back and forth, the real management process begins.

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VLAN Security Configuration of the nix-WLC-2012  The preceding configuration tasks dealt
with setting up the VLANs that are tied to the individual managed WAPs. This final
section of the controller setup wizard is used for setting up the security parameters,
such as authentication, authorization, accounting, and so on, to be used on the VLANs.
Note that the parameters set here affect the wireless STAs (clients) that will connect
to the managed WAPs. So the controller (and the wireless network administrator) must
consider the security capabilities of the wireless STAs.
The VLAN security configuration begins here:
1. This controller currently has two VLANs defined. Which of these would you
like to configure now? Press enter when done.
The options are {vlan1} {vlan2}
Hint: The SSID for vlan1 is area-1 and SSID for vlan2 is area-2.
> vlan1
2. Several authentication and encryption methods can be used to secure the
area-1 wireless network. Which of these would you like to use?
The options are {WEP 64 bits} {WEP 128 Bits} {WPA-Personal / TKIP}
{WPA-Personal / CCMP} {WPA-Enterprise / TKIP} {WPA2-Personal / TKIP}
{WPA2-Personal / CCMP} {WPA2-Enterprise / CCMP}
Hints: Make sure that whatever option you select is also supported by the
wireless clients.
Separate multiple options with commas, spaces, or semicolons.
> WPA-Personal / TKIP
3. Please create a secret key that will be used in encrypting and decrypting the
communications on area-1. Press enter when done.
Hint: The secret key is the passphrase. A good passphrase should be a mix of
alphanumeric characters and symbols and at least eight characters long.
> $never-never-land1$
4. Are you ready to save the VLAN security configuration for vlan1? Answering
YES will push the configuration settings to the managed wireless access point.
Hint: Make sure that the remote wireless access point is powered. Also make
sure that the AP is within reasonable physical distance to this controller to
ensure radio connectivity.
The options are {YES} {NO}
> YES

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5. The security parameters for vlan2 have not yet been set. Would you like to
configure security for vlan2 now? Press enter when done.
The options are {YES} {NO}
> YES
6. Several authentication and encryption methods can be used to secure the
area-2 wireless network. Which of these would you like to use?
The options are {WEP 64 bits} {WEP 128 Bits} {WPA-Personal / TKIP}
{WPA-Personal / CCMP} {WPA-Enterprise / TKIP} {WPA2-Personal / TKIP}
{WPA2-Personal / CCMP} {WPA2-Enterprise / CCMP}
Hints: Make sure that whatever option you select is also supported by the
wireless clients.
Separate multiple options with commas, spaces, or semicolons.
> WPA2-Personal/CCMP; WPA2-Personal/TKIP; WPA-Personal/CCMP
7. Please create a secret key that will be used in encrypting and decrypting the
communications for area-2. Press enter when done.
> !never-never-land2!
8. Are you ready to save the VLAN security configuration for vlan2? Answering
YES will push the configuration settings to the managed wireless access point.
Hint: Make sure that the remote wireless access point is powered. Also make
sure that the AP is within reasonable physical distance to this controller to
ensure radio connectivity.
The options are {YES} {NO}
> YES
And that’s all there is to it. We are done configuring the infrastructure devices for
our wireless network.
Summary
We began setting the stage for our enterprise-grade wireless network in this chapter.
We configured the infrastructure-side components, including installing a few devices
that are commonly found in large to medium-sized networks. Our infrastructure
hardware offered all the features, such as price, modularity, ruggedness, and so on,
that would make both the wireless network administrator and the upper management
folks happy.

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The infrastructure devices that we set up in this chapter will be used by our
network of heterogeneous clients (Windows, Linux, and Macintosh clients) in the next
three chapters. So it is very important that we get everything almost perfect in this
chapter.
The main players on our infrastructure side were a standalone WAP (nix-WAP-
2012), which is similar in features to the off-the-shelf residential gateways/firewalls
that are found in many homes and small to medium-sized networks. The configuration
process for our sample WAP is similar to real-world devices that serve the same
purpose.
The other major player in the infrastructure was a wireless LAN controller (nix-
WLC-2012) that can be used to manage up to 100 APs, but we used it to manage just two
APs in our sample network. The managed APs will each serve a wireless network with
two different SSIDs. We followed a generic configuration process while configuring the
nix-WLC-2012. Again the concepts discussed while configuring this unit will carry over
when you are configuring real-world wireless LAN controllers.

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Key Skills and Concepts
■■ Learn how to configure the wireless hardware components in Windows.
■■ Learn how to configure the software aspects for wireless networking in
Windows.
■■ Learn how to select optimal and compatible wireless settings. Use the netsh
utility for wireless network management.
■■ Explore SoftAP and Virtual WiFi features in Windows.
■■ Use wireless mesh networking in Windows.
■■ Learn about personal area networking in Windows.
Needless to say, a vast majority of desktop workstations in the world run a
Microsoft Windows-based operating system (OS). In this chapter, we will look
at setting up such systems as wireless client stations (STAs).
Windows Client Configuration
We will configure a computer running the Microsoft Windows 7 OS to connect to
a wireless network. Our sample system will be configured to connect to a generic
wireless access point (WAP) that was set up previously.
Table 13-1 shows the properties of the generic WAP, and Table 13-2 shows the
properties of wireless client STA.
Specification
Host name
SSID
Supported ciphers and authentication
Encryption key or passphrase
Wireless PHYs supported
Value
wap-3
area-3
WEP 64 / 128 bits
WPA-Personal / TKIP
WPA-Personal / CCMP
WPA-Enterprise / TKIP
WPA2-Personal / TKIP
WPA2-Personal / CCMP
WPA2-Enterprise / CCM
never-never-land
802.11b, 802.11g, 802.11a, 802.11n
Table 13-1.  WAP Specifications

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Specification
Host name
Operating system
Driver
Supported ciphers and
authentication
Compatible/optimal/suitable
cipher and authentication
Supported IEEE 802.11 standards
Compatible/optimal/suitable IEEE
802.11 standard
Wireless network name (SSID)
Value
Windows7-A
Microsoft Windows 7 Enterprise Edition
caffenix80211.sys
WEP
WPA-Personal / TKIP
WPA-Personal / CCMP
WPA-Enterprise / TKIP
WPA-Personal / TKIP
802.11b, 802.11g
802.11g
area-3
Table 13-2.  Wireless Client Specifications
Setting Up the Hardware
The rest of this chapter assumes that the wireless adapter on the client system is
already detected by Windows and that the appropriate driver is already loaded. This
will be the case for most original equipment manufacturer (OEM) computers (with
wireless capabilities) that ship with the OS already preloaded. In some cases, however,
a third-party wireless adapter must be used with an existing Windows-based system. It
is also possible that the factory-installed adapter and/or driver will go wonky during
the lifetime of the computer and will need to be replaced or reinstalled. In these kinds
of situations, you need to know how to set up wireless hardware, and that’s the focus
of the following discussion.
Naturally, before we get to the stage of fiddling with the drivers, we have to
physically insert the card into the system. Based on the various wireless adapter form
factors, we have our work cut out for us in this regard.
For adapters that can be plugged into an external port on the system, such as USB
and PCMCIA adapters, the physical task is simple.
For adapters that need to interface with the system via some internal and not
so easy to access port, such as PCIe, Mini PCI, and PCI, the task may be a little more
involved.

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The manufacturer for our sample adapter is again Caffenix, which makes the best
wireless adapters in the world. The wireless adapter model we’ll use is caffenix-80211.
Let’s walk through the steps required to install the driver software for our generic
wireless adapter.
1. Follow the hardware manufacturer’s instructions on how to properly
physically insert the wireless adapter into the computer.
2. After the card has been installed, power on the computer and log into the
system if necessary.
3. Wait for Windows to detect the new hardware and automatically attempt
to locate and install the driver. If Windows finds the correct driver, go on to
step 6.
4. If Windows fails to find and install the appropriate device driver automatically
from any of its standard locations (the built-in driver cache, removable drives,
or Windows Update site), the driver will have to be manually installed.
5. Make sure that you have the driver software available, either previously
downloaded from the vendor website or prepackaged by the vendor along
with the hardware on a media (such as a CD).
6. Click the Windows Start menu.
7. Type hdwwiz.cpl in the Search Programs And Files text box. Windows will
return a list of items that are related to your search term.
8. From the returned list, click hdwwiz.cpl. The Device Manager window will
appear.
9. Look for any device with an exclamation symbol (!) next to a name that is
related to WLAN. Once you find the device, right-click the device name and
choose Update Driver Software. An Update Driver Software dialog box will
appear.
10. Click the Browse My Computer For Driver Software option. A new screen
will appear, where you can point Windows to the exact location of the driver
software that you have from step 5.
11. On our sample system, the driver software is located on a vendor-supplied
disc in the D: drive of the computer. Specifically, the driver is located at
D:\\caffenix_Inc\\Drivers\\Windows7\\X64\\.
12. After you pointed Windows to the proper location of the driver, click Next.
13. Windows may prompt you with a Windows Security dialog box (see the
following illustration) warning you that it can’t verify the publisher of the
driver software. Click the option Install This Driver Software Anyway to
continue.

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If you don’t get any such warning, you may skip this step.
14. If all goes well, you should get a final screen informing you that “Windows has
successfully updated your driver software.” Click Close to finish.
15. The wireless adapter should now be ready for use.
Setting Up a Wireless Profile
After Windows has recognized the wireless adapter and has the proper drivers
installed for communicating with the adapter, you can begin configuring the wireless
client system running Windows by setting up a wireless profile.
You can connect a system to a wireless network in several ways in Windows 7.
Windows can do this automatically, or you can do it manually. Allowing Windows
to do the work can be easy and is a somewhat “dumbed-down” approach. In certain
scenarios, it can also lead to unintended consequences (such as connecting to an
unknown or hostile wireless network). We will opt for the manual approach here,
because it allows us to have better control of the process and offers us some insight into
what Windows is doing in the background.
The settings for individual wireless connections are stored in profiles in Windows 7.
So if, for example, we want to set up a wireless connection to a wireless gateway at
work, we could set up a profile specifically for this and call it “work.” In addition to
enabling connectivity with a wireless network, you can do many other cool things with
profiles.
Let’s walk through the process of creating a wireless connection profile on our
sample system and then manually connect to the wireless network associated with the
profile.
1. Log into the system with a user account with administrative privileges.
2. Open the Windows Start menu.

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3. Type wireless in the Search Programs And Files text box. Windows will return
a list of items that are related to your search term.
4. From the returned list, click Manage Wireless Networks. You’ll see a window
similar to the following:
5. Click the Add button, and the Manually Connect To A Wireless Network dialog
box will appear.

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6. Click the Manually Create A Network Profile option. A screen similar to the
one shown here will appear, allowing you to input the wireless settings.
7. Complete the fields of the dialog box with the appropriate information
provided in Table 13-2 earlier in the chapter.
8. For example, type area-3 in the Network Name field (SSID). Use only the
compatible/optimal/suitable values where appropriate. (See the sidebar titled
“Compatibility, Optimization, and Suitability Considerations” for guidelines.)
9. Make sure that the check boxes beside these options are cleared: Start
This Connection Automatically and Connect Even If The Network Is Not
Broadcasting.
Tip  Before the Windows client can successfully connect to a wireless infrastructure network
where the AP does not advertise the SSID, the Connect Even If The Network Is Not Broadcasting
option must be enabled, or checked.
10. Click Next when you have finished adding information to the fields.
11. At the ensuring Successfully Added “area-3” window, click Close.

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Note  By default, Windows gives the profile created through this process the same name as the
value of the SSID of the WLAN. If we wanted a more intuitive name, we’d have to rename the profile
at the end of the profile creation process.
  This could be done in the Manage Wireless Networks control panel, which is accessed by right-
clicking the name of the network profile and selecting the Rename option.
Wireless Network Management Utilities: Windows vs. Third-party Software
We’ve set up a wireless profile using the built-in wireless network management
utility in Windows 7. We can use other methods to achieve the same goal,
however.
One such method is to use the management software provided by the
wireless device’s vendor or manufacturer to configure a wireless network
interface on a Windows computer; Microsoft considers this method a “third-
party solution.”
When you install a vendor’s wireless network management software, you
might notice that you must choose to either use Windows’ built-in wireless network
management utility or the vendor-supplied wireless network management utility.
You should either use one or the other, but not both. Windows will sometimes
warn you if third-party software is currently being used for managing the wireless
interface on a Windows system.
Wireless hardware vendors probably know the ins and outs of their hardware
better than anybody else, including OS vendors. On the flip-side, OS vendors
probably know better than anybody else how third-party hardware should interact
with their OS internals. Herein lies the fork in the road.
Who should you trust to put in charge of managing the wireless network
interfaces on your systems? Go with whichever one works and whichever one
provides any extra functionality that you require.
If you want simplicity and seamlessness, use the built-in Windows utility. If
you want greater control and extra bells and whistles that the vendor provides,
stick with the vendor-supplied wireless network management software.
Despite the previous advice, you may sometimes find that in the real world,
you don’t have a choice between using a Windows built-in utility or a third-party
utility, because only one of the solutions actually works. The built-in Windows
utility may fail completely while the third-party utility may succeed—or vice
versa—despite your best efforts. This can help to greatly simplify the decision-
making process for you.

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Compatibility, Optimization, and Suitability Considerations
The directive to use only “compatible/optimal/suitable values where appropriate”
in step 8 of the “Setting Up a Wireless Profile” section is a classic example of
a decision that a wireless network administrator might have to make while
configuring a wireless client. Notice, for example, that our WAP supports a lot
more authentication and cipher methods than those supported by the wireless
client adapter.
So even though the WAP has built-in support for stronger or superior
authentication and encryption methods (such as WPA2-Personal/CCMP and
WPA2-Enterprise/CCMP) than those supported on the Windows client, the
WAP has to be forced to downgrade its own security when communicating with
the client to “WPA-Personal/TKIP” simply because the client cannot support
anything beyond “WPA-Personal/TKIP.” (For more on WPA, WPA2, and TKIP,
see Chapter 11.)
The same logic applies to IEEE 802.11 standards used on the wireless client. If
the client adapter is not capable of supporting much higher data rates like those
offered and supported by the WAP (such as IEEE 802.11n), the AP will be forced
to operate at a suboptimal data rate.
The solution to this common mismatch between the client-side devices and the
infrastructure-side devices can vary from simple and inexpensive, to complicated
and disruptive.
The solution may be as simple as upgrading or replacing the client-side devices
with newer hardware that can support the newer standards and functionality. This
solution, however, has the disadvantage of breaking support for existing legacy
client-side devices (such as devices running older, unsupported OSs), because it
may sometimes be impossible to upgrade the legacy client devices. It is possible that
the legacy devices or applications may have been originally designed deliberately to
function at low data rates and using weak encryption!
Another slightly more complicated and expensive solution may be for
the wireless network administrator to try to maintain a wide assortment of
infrastructure-side devices to keep everybody happy—the slow clients, the fast
clients, the secure clients, and the insecure clients.
Manually Connecting to a Wireless Network
Now let’s connect to the wireless network associated with the profile that we created
previously.
1. Log into the system.
2. Open the Start menu.
3. In the Search Programs And Files text box, type connect to a network.
Windows will return a list of items that are related to your search term.

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4. From the returned list, click Connect To A Network. A window will appear on
the lower-right side of the screen similar to this:
5. Among the list of wireless networks detected, find and select the area-3 network.
6. Click the Connect button. After a moment, Windows will connect to the
specified network—if everything goes well.
netsh Utility
netsh is a network configuration utility that ships with newer generations of Windows
OSs. And, of course, it comes bundled with Windows 7. It is a command line utility
that can be used in performing virtually all the network configuration tasks that can
be performed from the Windows graphical user interface (GUI). It can also be used for
many advanced tasks, including performing network configuration tasks on remote
systems. In addition to allowing you to view and manipulate network configuration,
netsh can be used for scripting purposes to help automate common tasks.
Network administrators who are aficionados of the command line interface (CLI)
may find that netsh provides a quick way to view and manipulate network settings of a
Windows-based computer. This is certainly true if you know your way around the tool
and are familiar with its numerous switches and options.
netsh controls certain aspects of the Windows networking stack, which are referred
to as contexts; these contexts are actually specific network components. Some contexts
that are available in Windows 7 are shown in Table 13-3.
We are, of course, mostly interested in the wlan context in this book.

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Context
interface
bridge
advfirewall
lan
dhcpclient
wlan
ras
Description
Manages the TCP/IP settings of network interfaces
Manages network bridge adapters
Manages IPsec, firewall, and other advanced security
network components
Manages the wired local area network interfaces
Manages the DHCP client
Manages WLAN interfaces
Manages remote access servers
Table 13-3.  netsh Contexts
Wireless Network Configuration Cloning with netsh
Windows makes it easy to clone the wireless configuration settings from one computer
to another. This can help speed up provisioning new wireless clients on a network. The
automated nature of the cloning process also reduces the chances of human errors when
entering network names, secret keys or passphrases, authentication, and cipher values.
Next we will perform a simple configuration clone from one system to another
using the powerful netsh command. Start by assuming we have two systems: The
primary machine (the source) is the same system that we configured earlier. This
machine is named Windows7-A, and it has all the proper wireless settings to connect to
our test wireless router, router-W.
The secondary machine (the target) is named Windows7-B. We are going to apply
the settings that were cloned from Windows7-A onto this machine.
Perform the following steps on Windows7-A, the source:
1. Log into Windows7-A with a user account with administrative privileges.
2. Choose Start | All Programs | Accessories.
3. Right-click the Command Prompt program and choose Run as Administrator.
4. Select Yes in the User Account Control (UAC) dialog box that opens.
5. A window similar to the one shown next will appear:

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6. Type the following command to view the existing wireless profiles stored on
the local computer:
> netsh wlan show profile
7. Then press enter.
8. The output should include the wireless profile named area-3 that we created
earlier in the chapter.
9. Next, dump (or export) the working profile into a format that can be easily
imported into another Windows system to configure it. Use the following
command to do this:
> netsh wlan export profile name="area-3" folder="C:\\Users"
interface="Wireless Network Connection"
This command will create a file named Wireless Network Connection-area-3.
xml, which will be stored under the C:\\Users\\ directory. Press enter when
you’re done typing the command.
10. We need to find a way to transport or copy the dumped profile file to the
Windows7-B target system—for example, by using a USB flash drive, a CD, a
DVD, a network share, or e-mail.
Now perform the following steps on Windows7-B:
1. Log into Windows7-B with a user account with administrative privileges.
2. Choose Start | All Programs | Accessories.
3. Right-click the Command Prompt program and select Run as Administrator.
4. Select Yes in the User Account Control (UAC) dialog box.
5. A command prompt window will appear.
6. Assuming that the wireless configuration profile that was created on the source
system (Windows7-A) was copied into a removable media or drive that shows
up as drive F: on our target system, we will load (import) the profile from that
location. This sample command shows how to do this:
> netsh wlan add profile filename="F:\\Wireless Network
Connection-area-3.xml"
Press enter when you’re done typing the command.
7. In the window that appears, type the following command to view the newly
created wireless profile stored on our target computer:
> netsh wlan show profile
Press enter when you’re done typing the command.

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8. You should now be able to join and use the same wireless network that the
source system (Windows7-A) uses.
Tip  The netsh utility can be used to display useful information about the IEEE 802.11 wireless
LAN interface and the device driver information. Among other things, it can also show the 802.11
PHYs supported, and the authentication and ciphers supported. The full netsh command to do
this is
netsh wlan show drivers
Wireless Odds and Ends in Windows 7
Every OS vendor tries to be the first kid on the block to implement support for the
latest wireless standards and technologies. Some vendors do a better job than others
in this area. Some vendors adopt a wait-and-see approach and wait for the standards
or technologies to become mature before incorporating support into their base OSs.
In this section, we will take a look at some of the new wireless features that ship with
Windows 7.
Virtual WiFi and Software Access Point
Microsoft brings virtualization to the desktop user with the Virtual WiFi (VWiFi)
feature in Windows 7. VWiFi uses hardware virtualization techniques to create a
virtual instance of the wireless adapter installed in the system. For VWiFi to work,
the underlying driver for the adapter has to support this feature; this, therefore, puts
some of the onus on the hardware manufacturer to create this support in its drivers.
Microsoft has created the framework and necessary hooks into its OS to enable this.
The basic idea behind VWiFi has been around for several years, so most of the
major wireless adapter vendors have some support for it, so it should easily work in
most newer systems that ship with Windows 7.
VWiFi essentially takes any supported and physically installed wireless adapter
and creates a virtual or software version of the adapter. The virtual adapter is directly
tied to the main wireless adapter, so if the main wireless adapter is disabled, the virtual
adapter is automatically disabled, too.
This virtual adapter shows up as Microsoft Virtual WiFi Miniport adapter in the list of
network devices in Windows 7 and later OSs.
Due to the natural laws of the universe and physics, virtualization is virtualization
is virtualization. This means the original hardware being virtualized will always be
the bottleneck in any system; and as such, things cannot run faster than the physical
hardware will permit. This is true regardless of what any of the vendor marketing
materials may try to tell you. Windows uses some smart internal routines to multiplex
the wireless network traffic between the physical and virtual adapters so that associated
delays and lags are not so apparent to the end user.

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The primary or physical wireless adapter functions in regular wireless STA mode.
This means that the adapter can act as a client or member of an infrastructure network
and connect to a WAP and perform its normal routines.
The other virtual adapter can, however, function in AP mode, and this is where the
name software access point (SoftAP) comes from. With the virtual adapter functioning
as an AP, other wireless STAs can connect to the SoftAP and form a separate or
independent wireless network. This network is the master of its own domain and can
have separate security requirements and policies.
The combination of all the new features that VWiFi and SoftAP provide is referred
to as a “wireless hosted network.”
You can do many cool things with the VWiFi adapter. We look at some of these
next.
Internet Connection Sharing
Internet Connect Sharing (ICS) is a feature in modern Windows OSs that facilitates
network sharing through a computer running a Windows OS. It essentially turns
a computer running Windows into a sort of router or gateway that is capable of
performing network address translation (NAT) functions.
Here’s how ICS would function in a wireless hosted network scenario:
1. The main node running Windows 7 or later is connected to the Internet via the
physical wireless adapter.
2. The main node’s access to the Internet is through the physical infrastructure
network.
3. The physical wireless adapter can act as a gateway to the VWiFi adapter to
provide a way (a route) to reach the Internet.
4. The VWiFi turns into a SoftAP.
5. Because the VWiFi adapter can reach the Internet, the other STAs connected to
the SoftAP can also access the Internet, as long as the OS policies allow this.
Configuring SoftAP and VWiFi Using netsh
Windows does not ship with an easy-to-configure point-and-click interface for
configuring the wireless hosted network functionality. Setting up SoftAP using VWiFi
requires the use of the netsh utility or some other third-party software. We will walk
through the steps involved in enabling a wireless hosted network in Windows.
Our sample wireless hosted network will be configured with the parameters shown
in Table 13-4.
Perform the following steps on the system running Windows 7 that will host the
wireless hosted network:
1. Log into Windows7-A with a user account with administrative privileges.
2. Choose Start | All Programs | Accessories.

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Wireless Hosted Network Parameter
SSID
Supported ciphers and authentication
Key or Passphrase
Support IEEE 802.11 standards
Value
windows-ap
WPA2-Personal CCMP
vwifi-secret
Same as those supported by the
physical wireless adapter/interface
Table 13-4.  Wireless Client Specifications
3. Right-click the Command Prompt program and select Run as Administrator.
4. Select Yes in the User Account Control (UAC) dialog box.
5. In the window that appears, type the following command to set an SSID of
windows-ap for the virtual WiFi interface, and then press enter:
> netsh wlan set hostednetwork ssid=windows-ap
6. Create a passphrase for the wireless hosted network by issuing the following
command at command prompt; press enter when you’re done.
> netsh wlan set hostednetwork key=vwifi-secret
7. Enable the wireless hosted network by typing this command in the Command
Prompt window. Press enter when you’re done.
> netsh wlan set hostednetwork mode=allow
8. Start the wireless hosted network by typing this command; press enter when
you’re done.
> netsh wlan start hostednetwork
9. In the command prompt window, type the following command to view the
settings of the wireless hosted network that was just configured:
> netsh wlan show hostednetwork
10. To view the values of the security parameters used for the wireless hosted
network, type this command, and then press enter:
> netsh wlan show hostednetwork setting=security
That’s it. The SoftAP should now be set up and broadcasting its SSID.

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Note  The wireless infrastructure network configured here facilitates only local communication;
it does not facilitate communication with any external networks such as the Internet. This mode of
operation is also known as “standalone mode.” Full-mode ICS is needed to enable interconnectivity
with external networks. The sidebar titled “Extended SoftAP, VWiFi, and ICS” provides a synopsis of
how to configure the ICS component.
You’ll perform the following steps on the client system that will connect to the SoftAP.
These steps are completely generic and OS-independent, so they can be carried out
on almost any wireless client that supports the authentication, cipher, and 802.11 PHYs
that SoftAP supports.
1. Use the wireless interface configuration utility for the wireless STA to search
for and select the network name (SSID) advertised by the SoftAP. The network
should show up as windows-ap in the list of available networks.
2. Connect to the windows-ap network.
3. When prompted for the key/passphrase to connect to the SoftAP, enter the key
that was created on the SoftAP: vwifi-secret.
4. The client STA will become a part of the infrastructure network formed by the
Windows-based SoftAP, as long as all the physical (802.11 PHY) and logical
(such as Encryption) attributes correlate between the two.
5. The preceding steps can be repeated for other client STAs that want to
participate in the wireless hosted network. All the client STAs will be able to
communicate with one another as well as with the SoftAP as long as the SoftAP
system is up and running.
Note that the steps here will not enable the client STAs to communicate with any
external networks, such as the Internet.
Extended SoftAP, VWiFi, and ICS
Here’s a quick run-through of the steps involved in configuring full-mode ICS,
which will allow the client STAs connected to the SoftAP to access external
networks such as the Internet.
The process is two part: The first part involves working from the command
prompt, and the second part involves using the GUI tools.
1. Complete the steps in the “Configuring SoftAP and VWiFi Using netsh”
section earlier in the chapter.
2. Make sure that system hosting the SoftAP has connectivity to the external
Internet via its physical wireless network interface.
3. ICS must be enabled on the physical wireless network interface that has
connectivity to the Internet.

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4. Choose Start | Search, and type ncpa.cpl in the Search Programs And
Files text box. Windows will return a list of items that are related to your
search term.
5. From the returned list, click the ncpa.cpl program icon to launch the
Network Connections Control Panel applet.
6. Locate the network connection that is associated with the physical
wireless adapter installed on the system. It might have a name similar to
Wireless Network Connection.
7. Right-click the Wireless Network Connection and select Properties. A
Wireless Network Connection Properties dialog will appear.
8. Click the Sharing tab in the Wireless Network Connection Properties dialog.
9. Click the check box for the Allow Other Network Users To Connect
Through This Computer’s Internet Connection option.
10. Under the Home Networking Connection section, click the arrow in the
Select A Private Network Connection drop-down list.
11. Select the network connection associated with the virtual WiFi Miniport
adapter (VWiFi). It might have a name similar to Wireless Network
Connection 2. The final window with all the proper options selected will
look similar to the one in this illustration:
(Continued)

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12. Click OK to close the Wireless Network Connection Properties dialog.
13. For good measure, you may want to stop and restart the wireless hosted
network service. This can be done by issuing the following commands at
the command prompt Press enter after each line:
> netsh wlan stop hostednetwork
> netsh wlan start hostednetwork
14. Issue this command to view the status of the wireless hosted network:
> netsh wlan show hostednetwork
15. In case you haven’t already done so, perform the four steps on the client
system that will connect to the SoftAP, as discussed earlier in the chapter.
From this point, other wireless client STA systems connected to the SoftAP
should be able to access external networks such as the Internet.
Mesh Networks
A mesh network is a type of network topology in which the nodes work together in
harmony to provide a communications link among all nodes. Each node or participant
in the mesh network has a role that it plays, but ideally no node is indispensable. The
individual nodes have micro-knowledge of their immediate neighbors. This micro-
knowledge facilitates communications among nodes at one end of the mesh to other
nodes at the extreme end.
Mesh networks are distinct from other network topologies because of their lack of
a central or all-knowing controller such as the APs or WAPs found in infrastructure-
based wireless networks. The main purpose of a mesh network is not necessarily to
provide access to the Internet for the nodes, even though Internet connectivity may be
a side benefit or feature that results from the mesh.
The nodes in mesh network can play various roles, such as client roles, router roles,
and gateway roles. Mesh networks offer several benefits such as redundancy, cost
savings, reliability, and scalability.
The SoftAP functionality built into Windows 7 and later OSs, can be used to build
mesh networks. These STAs running Windows 7 can act as repeaters of the wireless
radio signals, and one VWiFi can connect to the physical wireless adapter of another
STA, whose VWiFi can be used to connect to another STA’s physical VWiFi, and so on
and so forth.
Figure 13-1 shows a sample wireless mesh network using computers running
Windows 7 OS. In the figure, STA-1 is the original system with connectivity to the primary
infrastructure network that is managed by AP-1. The other systems, STA-2 and STA-3,
have interconnectivity with one another via their physical and virtual wireless interfaces.

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Virtual
instance of
wireless
adapter 1
Wireless
adapter
VWiFi
VWiFi
Physical
wireless
adapter 2
Virtual
instance of
wireless
adapter 2
Wireless
adapter
VWiFi
Physical
wireless
adapter 3
Virtual
instance of
wireless
adapter 3
Wireless
adapter
Physical
wireless
adapter 1
STA-1
STA-2
Infrastructure
network
AP-1
Figure 13-1.  A wireless mesh network
STA-3
Personal Area Networks (PAN)
Virtual WiFi can be used for linking or connecting miscellaneous types of devices in
addition to traditional STAs. This type of connection forms a type of peer-to-peer or
ad hoc network. When I say traditional STAs here, I am referring to regular mobile or
portable computing systems. The other classes of devices (nontraditional) that can take
advantage of the VWiFi functionality are consumer electronics devices that are used for
personal communications, such as wireless speakers, headsets, phones, printers, PDAs,
MP3 players, and so on.
This particular use will become more common place as more wireless device
manufacturers implement the new Wi-Fi Direct technology. Wi-Fi Direct helps to reduce
the need for traditional wireless infrastructure devices when creating wireless networks
to link different types of devices. Wi-Fi Direct can be used to connect various consumer
electronics to create a PAN, which can exist independently from the conventional
wireless network.

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Summary
This chapter covered some basic information you’ll need to configure the wireless
hardware and management software components of a system running Microsoft’s
Windows OS. Specifically, we connected a sample Windows client system to the
infrastructure wireless network that we judiciously set up in Chapter 12.
We also discussed installation and configuration options and procedures for several
wireless client systems.
All in all, wireless network configuration on the Windows platform is quite mature
and solid. Windows keeps a decent balance between staying on the cutting edge of
wireless technology while being reasonably conservative in other wireless technology
areas.
This means that several advanced features are built-in and supported by the OS
that should help keep any wireless network administrator busy, happy, frustrated,
delighted, entertained, and flustered.

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Key Skills and Concepts
■■ Understand the makeup of Macintosh systems.
■■ Review common Apple wireless networking hardware.
■■ Configure Apple OS X clients for wireless networking.
■■ Learn about Internet sharing in the Mac world.
■■ Review configuration of ad-hoc wireless networks.
■■ Learn how to configure Bluetooth Dial-up Networking in OS X.
Apple Computers’ market share is far from that of the dominant Microsoft
Windows, but the number and variety of network-capable devices made by
Apple and the fast rate of adoption of these devices make its products an
important part of a wireless network administrator’s job.
Apple devices come in all shapes and sizes, from servers, to workstations, to all-in-
one desktops, laptops, tablets, mobile phones, and portable entertainment units. One
thing all these devices have in common is built-in wireless functionality.
Macintosh System Design
Apple manufactures (or brands) the hardware as well as the underlying software that
drives their hardware. This has several implications, which we’ll examine in the following
sections.
Macintosh Software
Configuring and connecting a Machintosh (Mac) system to a wireless network can be
a simple process—a testament to why you don’t see job advertisements for Macintosh
wireless network administrator specialists.
The simplicity offered in Macintosh system has both good and bad sides. The good
side is the obvious simplicity and ease of use for the end user.
The disadvantage is a result of the technical sacrifices that had to be made to achieve
this simplicity.
Simple systems, by design, generally have less parts and features. It stands to reason
that fewer parts and features mean fewer things can go wrong or break. The network
or system administrator therefore does not have too much flexibility and configuration
options beyond what the Mac designers expose.
Macintosh Hardware
The other facet of Apple’s business model that directly affects the administrator’s work
has to do with the hardware. Mac hardware (and software that drives it) can be very
“Apple-centric.” Hardware parts and components that are compatible with Apple
devices are not as easy to find as commodity PC hardware.

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This fact probably has a lot to do with device driver issues, too. If all hardware
manufacturers also provided drivers for Macintosh systems, more hardware variety for
the consumer would appear on the shelves. But since Apple also manufactures its own
hardware, the company probably sees few good business reasons to encourage this.
Note  A similar issue used to plague the open source software community. Software developers
were willing and ready to create drivers for numerous hardware platforms, but hardware
manufacturers were resistant to providing details of the inner workings of their hardware to aid
the developers. From the hardware manufacturers’ perspective, the specific details of the inner
workings of their hardware gave the vendors their competitive advantage. This perceived advantage
also serves as the market differentiator between similar hardware makers.
  This issue hasn’t been completely eliminated in the open source software community, but it is
vastly improved now.
The Mac system wireless administrator is restricted to a limited range of compatible
hardware parts and accessories that Apple makes available, or to those sold by after-
market hardware vendors. So, for example, if a wireless administrator needs wireless
hardware that implements the latest IEEE 802.11.xxxxxxx standard, he or she might be
out of luck until Apple releases such a hardware or a firmware update that implements
the new functionality, or until some of the few after-market vendors offer the hardware.
Macintosh Wireless Hardware
Almost everything wireless produced by Apple likely includes the word “AirPort” in
its name. The current generation of wireless adapters for Macintosh systems has names
like these:
■■ AirPort  This was used to identify Apple’s first-generation wireless hardware
that implemented the original IEEE 802.11b standard. This AirPort hardware
operates in the 2.4 GHz wireless band.
Even though it may be technically inaccurate, this is still the generic name of
most modern Macintosh wireless hardware.
■■ AirPort Extreme  This generation of hardware is the successor of the original
AirPort cards. The AirPort Extreme hardware implements the next-generation
wireless standards—the IEEE 802.11a/g/n. Among other improvements, this
generation offers better data rates and security. Within the AirPort Extreme
family is the AirPort Extreme 802.11n hardware, which specifically implements
support for the IEEE 802.11n standard. The most current AirPort Extreme
hardware can operate in the dual 2.4 and 5 GHz wireless frequency bands;
as a result, AirPort Extreme is backward-compatible with the first-generation
AirPort wireless networks.
■■ AirPort Extreme Base Station  This is Apple’s implementation of a wireless
access point (WAP). Underneath the hood of the Extreme base station are the
typical electronics and radios that are found in other vendors’ residential access

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points (APs). But as with most things Apple, the base station has been wrapped
up in a pretty package.
Current versions of the base station can operate in dual-band mode, which
means that they support both frequencies in the 2.4 and 5 GHz range. It
supports the IEEE 802.11a/b/g/n wireless standards.
■■ Time Capsule  This multipurpose wireless device is primarily a wireless
network storage device that can also function as WAP. In other words, it’s an
AirPort Extreme Base Station with a big hard drive inside it.
The network storage component of time capsule works in conjunction with
software installed on a compatible Mac computer to perform automatic data
backups from the client system to the time capsule.
The current generations of the time capsule hardware are multi-band devices
that can operate in the 2.4 and 5 GHz frequency bands.
Mac OS X Wireless Client Configuration
In this section, we will connect a Mac OS X computer to a wireless network. Our sample
system will be configured to connect to the generic WAP that we set up in Chapter 12.
Table 14-1 shows the properties of our WAP, and Table 14-2 shows the properties of
our Macintosh wireless client STA.
Setting Up the Hardware
Out of the box, Macintosh systems already have the appropriate drivers installed for
the hardware, so there’s really nothing for you to do. The rest of this chapter assumes
Specification
AP host name
SSID
Supported ciphers and authentication
Encryption key or passphrase
Wireless PHYs supported
Table 14-1.  WAP Specifications
Value
wap-2
area-2
WEP 64 / 128 bits
WPA-Personal / TKIP
WPA-Personal / CCMP
WPA-Enterprise / TKIP
WPA2-Personal / TKIP
WPA2-Personal / CCMP
WPA2-Enterprise / CCMP
!never-never-land2!
802.11b, 802.11g, 802.11a, 802.11n

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Specification
Host name
Operating system
Wireless card vendor and type
Wireless card chipset/driver
Supported ciphers and authentication
Compatible/optimal/suitable cipher
and authentication
Supported IEEE 802.11 standards
Compatible/optimal/suitable IEEE
802.11 standard
Value
book01
Mac OS X - Snow Leopard
Apple / AirPort Extreme
Atheros
WEP
WPA-Personal / TKIP
WPA-Personal / CCMP
WPA-Enterprise / TKIP
WPA2-Personal / TKIP
WPA2-Personal / CCMP
WPA2-Enterprise / CCMP
WPA2-Personal
802.11b, 802.11g
802.11g
Table 14-2.  Wireless Mac Client Specifications
that the wireless adapter on the Macintosh client system is the one that shipped with
the system.
Setting Up a Wireless Location
Other mainstream operating systems (OSs) associate different network configurations
with profiles. The equivalent of profiles in the Mac world is a “location.” On a Mac, a
set of network settings and different devices are associated with a location. A defined
location allows the ordering of the various connectivity devices and interfaces within it.
For example, at a location named home, wireless connectivity would be preferred over
wired connectivity; and at a separate location called office, Ethernet connectivity is
preferred over wireless. A default location called “Automatic” exists on Macintosh
systems, and we’ll use this default location in our sample system.
Mac OS X offers several ways of connecting to a wireless network: it can be done
automatically or you can do it manually. Allowing OS X to configure a system to
connect to a wireless network can be easier for you, but in certain scenarios it can also
lead to unintended consequences, such as connecting to an unknown or hostile wireless
network. We will opt for the manual approach here, because it allows us better control
of the process and offers some insight into what OS X is doing in the background.

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AirPort Utility
Macs ship with a built-in AirPort utility that can be accessed by choosing
Applications | Utilities.
It is easy to assume that the utility is used for managing the AirPort wireless
adapter built into the computer. However, the AirPort utility is used to manage a
separate proprietary hardware sold and marketed by Apple called the AirPort.
This AirPort device is nothing more than a standalone WAP or residential
gateway device that can be used to create simple wireless networks for sharing
Internet access and other resources. Wireless networks created and controlled by
AirPort base stations are, however, not proprietary. The networks are accessible
by regular Microsoft Windows clients, Linux/UNIX/BSD clients, and other IEEE
802.11-compliant devices.
Like other management interfaces for configuring and managing wireless
infrastructure devices, the AirPort utility can be used for configuring Dynamic
Host Configuration Protocol (DHCP) options, radio settings, access controls,
authentication, and encryption settings for the AP.
Manually Connecting to a Wireless Network
Let’s connect to the wireless network associated with the AP that was configured in
Chapter 12. The SSID of that network is area-2.
1. Log into the system.
2. Click the Apple menu at the upper-left corner of the screen and choose System
Preferences. A System Preferences window similar to the following appears:

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3. Click the Network icon under the Internet & Wireless category. The Network
preferences window appears, showing the available network interfaces/
devices on the system in the left pane.
4. Click the AirPort network device in the left pane. The network window will
display some of the configuration options available for the AirPort adapter.
5. In the AirPort network screen, make sure that the AirPort device status is set to
On. If the status is set to Off, click the Turn AirPort On button.
6. Click the Advanced button at the bottom of the window. An AirPort
configuration screen will appear with a list of preferred networks (if any).

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7. Click the plus (+) sign under the Preferred Networks section. The following
dialog box will appear, where you can input the settings for the wireless network:
8. Enter the SSID in the Network Name field. Click the arrows in the Security drop-
down list and select the security type used on our sample network (see Table 14-1).
9. Click the Add button after completing all the fields. You will be returned to the
AirPort network configuration window. Clear the Remember Networks This
Computer Has Joined check box. The window should look like this:

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10. Click OK to close the AirPort network window.
11. Click Apply in the main Network window to initiate and complete the client’s
wireless connection with the infrastructure wireless network (area-2).
12. Close the system preferences window.
Changing Connection Preferences
In Mac OS X systems, the default ordering for network interfaces in a given
location is Ethernet, Firewire, and AirPort. You can change the default order by
following these steps:
1. While logged into the system, click the Apple menu at the upper-
left corner of the screen and select System Preferences. The System
Preferences window will appear.
2. Click the Network icon under the Internet & Wireless category. The
Network preferences window will appear, showing a list of the available
network interfaces in the left pane.
3. In the bottom-left corner of the window, click the arrow next to the little
flower or sun-shaped icon and select Set Service Order from the drop-
down list. A Service Order dialog will appear:
4. Click any of the available interfaces and drag it to the desired position.
5. Click the OK button when you are done.
6. Click the Apply button in the Network preferences window and then
close the window.

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Wireless Odds and Ends in OS X
Most OS vendors try to be the first to implement support for the latest wireless standards
and technologies. Other vendors wait for the standards or technologies to become mature
before incorporating support into their base OSs.
Mac OS X falls into the conservative category. Apart from making it easy to
configure network settings, the OS does not offer many extra bells and whistles in the
way of advanced features for the network administrator. But it does offer a few extra
wireless networking functionalities. We’ll take a brief look at a few of these.
Internet Sharing
Macs have their own implementation of Internet connection sharing that allows an OS
X system to become an Internet gateway of sorts to other systems on a network. This
functionality, however, is not quite as polished or feature-rich as that of other popular
mainstream OSs, such as FOSS/Linux-based systems or Windows systems.
Internet sharing on Macintosh systems works like this:
1. The Mac connects to the Internet via any of the interfaces available on the
system—AirPort card, Ethernet, Bluetooth, dial-up modem, and so on.
2. Computers that need to access the Internet connect via the Mac host using any
of the other ports that are not being used by the Mac to connect to the Internet.
The key word here is other.
3. So, for example, if the Mac host is connected to the Internet via an Ethernet
connection, other systems can access the Internet via the Mac’s wireless AirPort
interface.
The Macintosh’s AirPort connection is shared by other connected computers via an
Ethernet Local Area Network (ELAN). To share an Internet connection over Ethernet,
the Mac needs to be connected to the Internet by some other means, such as AirPort,
Bluetooth, cellular network, and so on. The converse is also true: To share an Internet
It’s All About the Sharing
Internet connection sharing is called Internet sharing in the Macintosh world. In
this world, we don’t share the connection, instead we share the Internet. Sharing
refers to accessing and using network and other system resources provided by
other Mac systems. So, for example, if you want to turn a Mac system into a web
server, you’d turn on the Web Sharing service.
So instead of saying we want to “enable the complicated routing, Network
Address Translation/Port Address Translation (NAT/PAT) firewall gateway
functions” in a Macintosh system, we can simply say we want to “enable Internet
sharing.”

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connection over the AirPort interface, the Mac needs to be connected to the Internet by
some other means, such as wired Ethernet, Bluetooth, cellular network, and so on.
Let’s walk through the steps for enabling Internet sharing on our sample Macintosh
system. The network we will set up will resemble the one shown in Figure 14-1.
1. Click the Apple menu at the upper-left corner of the screen and select System
Preferences.
2. In the System Preferences window, click the Network icon under the Internet &
Wireless category. The Network preferences window will appear.
3. Click the AirPort network device. You’ll see some of the configuration options
available for the AirPort adapter.
4. Make sure that the AirPort device is turned on. The Status should read
“Connected” and should also show that AirPort is connected to an
infrastructure network (for example, area-2). If the status is set to Off,
click the Turn AirPort On button.
5. After making sure that the AirPort is properly connected to a network, click
the Show All button at the top of the window to return to the main System
Preferences window.
6. Click the Sharing icon under the Internet & Wireless category. The Sharing
window will appear.
7. In the left pane, look through the list of available services and click the Internet
Sharing service. The Internet Sharing configuration options will appear on the
right side of the window.
Internet connected
WAP
Ethernet
connected
clients
Macintosh system connected to the
WLAN via AirPort and
connected to LAN via Ethernet
Figure 14-1.  Internet Sharing
Internet

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8. Click the drop-down arrow in the Share Your Connection From field and select
the AirPort option.
9. In the To Computers Using field, click the Ethernet checkbox to enable it.
10. Make sure that the Internet Sharing service is still highlighted in the left pane
of the window. Click the checkbox next to Internet Sharing to start the service.
A caution screen will pop up, asking if you are sure about turning on Internet
Sharing. Click the Start button.
11. The final Sharing preferences window will resemble the one shown here. Close
this window when you’ve finished making changes.

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All systems that are connected to the same Ethernet segment (via a switch or
directly) to the Mac will automatically get IP configuration information from the Mac
system. All systems connected via the Mac system should now be able to access any
networks (such as the Internet) that the Mac system can access.
Ad-Hoc Networks
Apple’s OS makes it easy to set up ad-hoc networks (also known as computer-to-
computer) networks. Ad-hoc networks make creating a wireless network of systems
quick work, without the need for a traditional infrastructure device such as an AP.
Unfortunately, the ad-hoc networks that can be created by Mac systems cannot be
protected with any of the newer high-grade encryption technologies. At the time of this
writing, only 40-bit and 128-bit WEP can be used in securing ad-hoc networks.
Ad-hoc networking and traditional infrastructure-based WLANs are mutually
exclusive in Mac computers. Enabling and hosting an ad-hoc wireless network on a
Mac disconnects the system from any other infrastructure networks.
We’ll create our ad-hoc network with the configuration settings shown in Table 14-3.
Use the following steps to set up an ad-hoc network on a Mac system:
1. Click the Apple menu at the upper-left corner of the screen and choose System
Preferences. Click on the Network icon under the Internet & Wireless category.
2. In the Network preferences window, click the AirPort network device to see
some of the configuration options available for the AirPort adapter.
3. Make sure that the AirPort device Status is set to On. Click the Turn AirPort On
button if the status is set to Off.
4. In the Network Name field, click the drop-down arrow and select Create
Network at the bottom of the list. A Create a Computer-to-Computer Network
window will appear.
5. By default, the Network Name (SSID) field will show the host name of the
computer. Change the name (SSID) to ad-hoc-mac.
Specification
SSID/network name
Channel
Password
Security
Value
ad-hoc-mac
Accept the default value
128-mac-adhoc
128-bit WEP
Table 14-3.  Ad-Hoc Network Settings

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6. Click the Require Password checkbox to enable that option. Complete the rest
of the fields with the values from Table 14-3 and shown here:
7. Click the OK button to close the window. Then click Apple in the Network
preferences window.
8. Close the Network preferences window.
The ad-hoc network will now be active and ready for other wireless clients to join it.
Mac Ad-Hoc Network Considerations
The process for connecting to ad-hoc networks is not much different from
connecting to regular infrastructure wireless networks. The same tools used for
connecting to infrastructure networks are used. Theoretically, you should just
locate the network name (SSID) in the list of detected networks and input any
security parameters, and the WLAN client should be good to go.
However, because ad-hoc networking is not covered by any IEEE 802.11
standard, your mileage may vary when connecting different clients from other
non-Apple platforms to a Macintosh computer–hosted ad-hoc network.
The wireless clients participating in a Mac-hosted ad-hoc network use
dynamic-link-local addresses (aka self-assigned IP address). These link-local
addresses are in the 169.254.0.0/16 range and are covered in the IETF document
RFC 3927.

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Bluetooth Dial-up Network
The Dial-Up Network (DUN) Bluetooth profile allows a Bluetooth device to be used as
a data modem with other compatible Bluetooth devices such as laptops and personal
digital assistants (PDAs). Connecting (or teetering) to Bluetooth mobile devices uses
the cellular data network and as such can incur additional charges beyond the regular
voice plans offered by cellular network providers.
Note  Don’t forget to disconnect the connection properly when you’re done with this process to
avoid unnecessary charges from the mobile network operator.
Here’s how to set up a Bluetooth DUN:
1. Click the Apple menu and select System Preferences.
2. Click the Network icon under the Internet & Wireless category. The Network
preferences window will appear.
3. In the left pane, click the plus (+) sign at the bottom left to add a new network
interface type.
4. In the dialog box that appears, click the Interface drop-down list and choose
the Bluetooth DUN interface type. Accept the default Service name of
Bluetooth DUN in the Service Name field. The completed dialog box will look
like this:
5. Click the Create button. Back in the main Network preferences window, click
the Apply button.
6. Click the newly created Bluetooth DUN interface in the left pane.
7. Click the Set Up Bluetooth Device button.
8. Make sure that the Bluetooth-enabled mobile device is powered on and set in a
discoverable mode.

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9. In the Bluetooth Setup Assistant window, the Mac system will search for and
display a list of Bluetooth-enabled devices in the vicinity. When the desired
device has been discovered, highlight the device in the list of devices (see the
illustration) and then click Continue.
10. A passkey will be automatically generated by the Macintosh system to
complete the pairing process with the target Bluetooth device (such as a mobile
phone). The generated passkey needs to be entered on the target Bluetooth
device exactly as displayed in the Macintosh Bluetooth Setup Assistant
window (see the illustration). Return to the Macintosh after entering the
passkey for the target device and click Continue.

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11. The Bluetooth Setup Assistant process will continue to the Bluetooth Mobile
Phone Setup stage. This is where things get personal and you will supply the
values that apply to your particular mobile or cellular provider. Click Continue
when you are done. On our sample system, we use the following values:

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12. A final Conclusion window will appear, informing you that pairing was
successful. You’ll also see some of the capabilities (supported profiles) of the
target Bluetooth device. Click Quit.
13. Back at the main Network preferences window, make sure the Bluetooth DUN
interface is selected in the left pane, and then click Connect in the right pane.
14. If everything checks out, the Macintosh system will connect to the Internet via
a Bluetooth connection to the mobile device using the cellular network.
Tip  Feel free to experiment with the list of available phone vendors or mobile/cellular network
operators, just in case the exact provider for your phone is not listed (see step 12 of the Bluetooth
DUN section). Because most of the mobile network providers use similar underlying technologies,
you might find that if you select a phone vendor in your area, the settings and connection
parameters might work with your specific provider.
Summary
It takes a lot of effort to design an almost foolproof system for such a wide demographic
of people, and the engineers at Apple Corporation have created a system that works
right out of the box—as long as you don't plan on doing too much beyond what the
engineers intended the system to do. A Mac network doesn’t leave much work for a
wireless network administrator—no room, for example, to show off or demonstrate any
advanced wireless networking expertise.

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Key Skills and Concepts
■■ Learn about wireless hardware on Linux platforms.
■■ Learn about the Linux Wireless Extensions application programming
interface (API).
■■ Learn about some popular Linux wireless drivers.
■■ Review proprietary wireless firmware in Linux-based distributions.
■■ Review the tools used for managing wireless settings in Linux clients.
■■ Walk through configuring a wireless Linux client using GUI tools.
■■ Walk through configuring a wireless Linux client using command line tools.
■■ Learn how to set up an ad-hoc wireless network using Linux clients.
Gone are the days when installing and configuring new hardware in Linux-
based systems required excessive preparation, endless cups of coffee, studying
README files and other documentation, compiling and cross-compiling,
reverse-engineering, researching help forums, and muttering unprintable words.
These days, it’s pretty much plug and play.
Linux is at the heart of most Free and Open Source Software (FOSS) distributions,
and as such, Linux is responsible for controlling the interactions between hardware
components and the other parts of the operating system (OS).
Thousands of Linux-based distributions are available today. The distributions are
backed by different commercial and noncommercial entities and hobbyists. They pull
together different FOSS projects and applications and package them into a distribution
format. The objective of most distributions is to produce an easy to install, easy to use,
easy to distribute, multipurpose or single-purpose set of software.
One of the great advantages of FOSS is that it gives you the freedom to be as hands-
on or as hands-off as you like. You can get down and dirty with the working details, or
you can choose to point-and-click from predefined menu options to get the job done.
We’ll use a hands-on approach in this chapter and provide more information than is
necessary to configure a Linux-based client for wireless networking. Hopefully, you’ll
gain some insight into how things work internally, to help you glue the theoretical
components of wireless networking with the practical aspects so that you can be adept
at troubleshooting and marketable as a wireless network administrator.
The concepts and fundamentals discussed in this chapter can also be applied to the
inner workings of other OSs; the difference is in how other closed systems might force
you to take a hands-off approach to learning and implementing.

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Wireless Hardware on Linux Platforms
Wireless hardware used to be especially tricky to get working on Linux-based systems
for several reasons. Open source hardware developers were willing and able to write
drivers for the wireless hardware, but hardware vendors were not forthcoming with
the details of the inner workings of their hardware to support this. Some device
manufacturers thought that revealing the inner workings of their hardware meant
giving up their market advantage to the competition.
Fear, uncertainty, and doubt (FUD) have also played a part. Various countries have
designated local legislative bodies that allocate and manage the use of the radio spectrum
within the country. This is important for organizational, safety, and practical purposes,
for example, so that amateur radio enthusiasts don’t transmit their messages on the same
frequency channels used by local emergency services.
Some wireless hardware vendors exhibit FUD characteristics because they believe
that Linux drivers cannot adhere to the requirements for radio spectrum use. The FUD
factor comes into play because some hardware vendors cannot see any way for the
open source developer community to enforce the rules because of the very nature of
FOSS. Such vendors believed it would be easy for end users to alter underlying code
that enforced the rules that force compliance with local radio spectrum use.
All FUD aside, the FOSS community has gone to great lengths in recent times to
reach out and assuage the concerns of wireless hardware vendors. Practical safety
measures now included in the Linux kernel code ensure that the code can’t be changed
in unacceptable ways.
Linux Wireless Drivers
A common joke in the FOSS community is that any single problem can be solved in 300
different ways. This joke belies the good and bad aspects of FOSS.
The obvious good part is the choice and power that FOSS gives the users. The bad
aspect is the confusion, disjointedness, and seeming incoherence that can result from
having so many approaches and solutions. But die-hard FOSS purists point out that
the competition that this breeds is healthy and that eventually only the very best of the
solutions (software projects) will survive and last.
FOSS drivers for wireless hardware are affected by issues similar to those that affect
regular software applications. This means that, in some instances, multiple device drivers
are available for the same wireless hardware family. Sometimes, multiple application
programming interfaces (APIs) exist in the Linux kernel space for drivers to use.
Mainstream FOSS wireless driver families and APIs will be discussed, beginning
with the existing API families.
Linux Wireless API
A wireless API in the Linux world provides a standard way to manipulate wireless
networking hardware. The API presents a device driver–independent method of

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implementing the 802.11 standard in the Linux kernel. APIs provide device driver
developers a standard set of tools to use for communicating with the Linux kernel so
that they don’t have to start from scratch when adding standard functions. Some of the
popular API families are discussed next.
Wireless Extensions API
The Wireless Extensions API represents one of the earliest attempts at creating a
wireless API for Linux and is possibly the most popular and widely deployed API.
Wireless Extensions has been ingrained in the Linux kernel since version 2.0.03.
Wireless Extensions APIs are no longer under active development. Even though
new features are no longer being added, newly discovered bugs are still being fixed
because of the large user base that depends on the API.
The Wireless Extensions API comprises three parts:
■■ User interface  Userland tools for manipulating certain wireless hardware
settings (see Table 15-1)
■■ Kernel interface  The Linux kernel resident parts of the Wireless Extensions API
■■ Driver interface  Specific hooks in the hardware device drivers that
developers must include in the driver code to enable them to take advantage of
the benefits of the extensions
Mac80211
Mac80211 is the Linux wireless API du jour. It is the wireless subsystem in the Linux kernel.
The most current work in the Linux wireless API space is in developing the mac80211
software stack, which is being groomed as the successor to the Wireless Extensions API.
Wireless Extensions Utility
iwconfig
iwlist
iwevent
Description
Used primarily for configuring certain wireless
characteristics of wireless network interfaces,
such as the frequency or channel, operating
mode, transmit power, sensitivity, modulation,
extended service set ID, to name a few. Also used
for displaying basic information about the wireless
interface.
Used for querying and displaying extended
information about wireless network interfaces.
Used for debugging. It displays wireless events
generated by drivers and settings changes.
Table 15-1.  Wireless Extensions API Userland Tools

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In its current state, mac80211 is geared toward SoftMAC devices, which are network
devices that depend on software or firmware to implement a part of their functionality.
Mac80211 therefore provides the framework with which developers can write drivers
for SoftMAC wireless devices.
Like its predecessor (Wireless Extensions), mac80211 comprises several components:
■■ cfg80211  This is the new Linux wireless configuration API component of the
mac80211 framework. In addition to configuration, cfg80211 also helps with
registering the wireless subsystem (mac80211) with the networking subsystem
of the Linux kernel.
An important function of cfg80211 is in addressing the regulatory compliance
concerns of wireless hardware vendors (discussed in the section “Wireless
Hardware on Linux Platforms”). Out of the box, wireless hardware can support
different radio frequency channels, but cfg80211 handles compliance issues
by ensuring that the wireless hardware operates only in the allowed radio
channels for the currently set regulatory area.
■■ nl80211  The user-space tools interact with cfg80211 via the nl80211 interface
in the new mac80211 framework.
■■ iw  A set of command line interface (CLI) userland tools for querying and
configuring the interface and radio properties of a wireless network device.
iw offers similar functionality to that offered by the iwconfig utility under the
Wireless Extensions API.
Common Linux Wireless Drivers
There are countless wonderful open source wireless drivers available today, but we’ll
only discuss the popular driver families and their associated chipsets. Remember that
only a handful of vendors manufacture wireless chipsets, and everybody else integrates
those chipsets into their products. As a result, you will find that one driver family is
able to support multiple wireless hardware from seemingly different vendors.
One of the unique attributes of the FOSS world is that, instead of the actual device
manufacturers spearheading the process of shipping and maintaining the drivers
for their products, the FOSS community often takes the initiative to do this. You will
therefore find some wireless hardware drivers that are part of open source projects.
MadWifi Driver Project
The MadWifi—Multiband Atheros driver for WiFi—family supports wireless devices
with chipsets manufactured by Atheros Corporation. The Atheros chipsets are found
in numerous wireless devices all over the world, including products manufactured by
Apple, Netgear, Toshiba, HP, Linksys, and D-Link, to mention a few.
Some of the drivers to emerge from the MadWifi project, such as the following, are
not considered fully open source, because a part of their functionality is implemented
in a closed source binary format. The closed source part is implemented as a hardware
abstraction layer (HAL). Despite this fact, Wi-Fi hardware sporting the Atheros chipsets

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are popular in the FOSS community, because they offer a wide range of advanced
features and are easy to extend. Atheros is also regarded as a FOSS-friendly company.
■■ madwifi  The original set of drivers from the MadWifi project. These drivers
rely on the HAL component to function, and although they are no longer under
active development, they still have a large install and user base.
■■ ath5k  This driver is tagged as the replacement for the original madwifi
driver. Unlike madwifi, ath5k does not depend on a closed source HAL
component to function. This therefore makes it a completely open source
driver. The driver supports Atheros wireless chipset types with model numbers
of AR5xxxx.
■■ ath9k  This is the Atheros driver for the next-generation wireless chipsets that
supports the IEEE 802.11n standard. It is also a completely FOSS driver since
it does not require a closed source, binary-only HAL to function. The driver
supports Atheros wireless chipset types with model numbers of AR9xxxx and
some AR5xxxx models.
Broadcom Drivers
Broadcom is a popular manufacturer of the chipsets used by various OEMs in their
finished products—such as Acer, Apple, Asus, Belkin, Buffalo, Dell, HP, Microsoft,
Linksys, and USRobotics, to mention a few.
The Broadcom chipsets make use of firmware. (See “Firmware and HAL” for more
on firmware.)
Broadcom wireless chipset–based wireless devices have a high success rate for
working in FOSS platforms, even though Broadcom as a company has not been
helpful in driver development. As a matter of fact, most of the Broadcom drivers were
developed by reverse-engineering efforts by members of the FOSS community. In fact,
wireless devices with USB interfaces that sport Broadcom chipsets are notoriously
known to be unusable with FOSS.
Following are two of the drivers for wireless chipsets made by Broadcom:
■■ b43legacy and bcm43xx  The b43legacy driver is considered as a legacy driver
for older hardware and older kernels. Specifically, b43legacy supports wireless
hardware that implements only the IEEE 802.11b standard and other so-called
revision 2 chipsets. bcm43xx is a much older driver that is no longer used in
newer Linux kernels.
■■ b43  This is the current driver that is used for driving newer Broadcom
wireless chipsets and hardware.
Intel Wireless Drivers (iwlwifi Project)
Intel wireless drivers are mostly released and managed as open source software
projects, supported by Intel. However, the chipsets themselves often require a closed
source firmware component. The most recent wireless drivers for Intel hardware comes

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packaged with recent Linux kernels and FOSS distributions. The official project name
under which all recent Intel wireless driver development takes place is called iwlwifi,
and the newer iwlwifi drivers make use of the new mac80211 wireless API subsystem.
Following are some of the drivers for wireless chipsets made by Intel:
■■ ipwXXXX  This driver family is used by early generation wireless networking
chipsets made by Intel, such as those in Intel PRO/Wireless 2100, 2200,
and 2915 hardware series. This driver family does not make use of the new
mac80211 API.
■■ iwl3945  This driver is for the Intel PRO/Wireless 3945ABG/BG family of
wireless hardware chipsets and replaces the older ipw3945 driver for the same
hardware family.
■■ iwlagn  This driver is for the Intel Wireless WiFi Link AGN hardware family,
such as 5100BG, 5100ABG, 5100AGN, 6000AGN, 4965AGN, and so on. It
supports the newer generation wireless chipsets that implement the IEEE
802.11n standard.
Firmware and HAL
Firmware is a type of software that runs directly on the hardware (microcontroller,
or the digital signal processor) for which it is written. Any hardware designed to
use firmware needs the firmware for its basic functionality. The firmware’s role is
not usually that of enforcing policy issues or protecting the host system in which
it is being used.
The HAL is also a type of software, but it is intended to be executed on the
central processing unit (CPU) of the host like other regular system software. As
implied in its name, the HAL provides a layer of abstraction between the hardware
and other system processes. This abstraction or protective layer can be used, for
example, to make sure that a wireless radio does not operate in radio frequencies
that are noncompliant with requirements or legislation in a certain area.
Open source OS distributions cannot legally package proprietary firmware
for chipsets along with other distribution software, because the firmware is often
copyrighted by the device manufacturer. Closed source OSs such as Microsoft
Windows and MAC OS X do not have these issues, because the hardware
manufactures often package the device firmware with the device drivers that are
sold or shipped with the finished products.
Some of the mainstream distributions work around this proprietary firmware
limitation by creating simple methods for users to legally “obtain” the firmware
from legal sources (the hardware vendor). One such popular mechanism for
obtaining the firmware is by using the b43-fwcutter utility.
Because Windows drivers for wireless hardware can be easily downloaded
from the vendor’s web site, b43-fwcutter can be used to extract the firmware
packaged with the Windows driver.
(Continued)

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The extracted firmware is then placed in a specific location on the file system,
so that it can be loaded or executed by the chipset hardware.
This is the current workaround as of this writing. It is possible that things can
change in the future for better or for worse, such as the following:
■■ Wireless hardware manufacturers may find ways (legal or technical) to
prevent tools such as b43-fwcutter from functioning.
■■ Wireless hardware manufactures may decide to start directly supporting
FOSS users better and create drivers with or without firmware for FOSS-
based distributions.
Wireless Network Management Tools
Every OS has its own set of tools or utilities to aid the user in configuring the wireless
network devices on the host. Linux-based distributions are no exception. And, as you
may have come to expect of FOSS platforms, not only do we have one tool, but we have
several tools from which to choose.
The FOSS community started with a lot of different wireless configuration tools,
and as the laws of natural selection would have it, only a handful have survived and
gained popular acceptance. The GUI tools used for configuring wireless devices in
Linux are referred to collectively as Wireless Network Managers. And the command
line tools are referred to as, you guessed it, CLI utilities. Incidentally, most of the nice
GUI network managers still call and depend on the CLI utilities in their back-ends!
We’ll briefly look at some of the wireless configuration tools and managers next.
NetworkManager
This GUI-based network management application is possibly the most popular and
widely deployed of all the management tools.
Over the years, it has become so neatly integrated with the rest of the graphical
desktop experience in FOSS distributions that it is easy to forget it is even there! The
design goals of nm include ease of use, visual clarity, and a motto that things should
“just work” with as little interaction as possible.
NetworkManager, or nm, is used to manage various types of network communication
interfaces, such as mobile broadband, Wi-Fi, modems, virtual private networks (VPNs),
and so on. It does this via a plug-in architecture that makes it future-proof, because as
new networking protocols and interface types emerge, plug-ins can be developed to
integrate with nm.
nm expects that the relevant drivers for the underlying hardware are already
functional. It does not concern itself with such things and leaves these low-level details
to the OS. So buyer-beware, because if you run out and purchase the latest and greatest
wireless network adapter that implements the nonexistent IEEE 802.11h.u.g,e standard,

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nm will not necessarily help you. However, it will help as long as the drivers exist for
the card and are usable by the kernel.
Wireless Interface Connection Daemon
Wireless Interface Connection Daemon (wicd, pronounced “wicked”) is an alternative
open source wired and wireless network management application for FOSS-based
distributions. It also has its own large user following, but its install base is not as large
as that of nm. It has a few outstanding features:
■■ Offers seamless integration with all the different desktop environments
■■ Has no dependencies on the popular GNOME desktop environment
■■ Offers a powerful command line console interface
More information about wicd can be found at the project web site at http://wicd
.sourceforge.net.
ConnMan
This is the newest kid on the block in the FOSS network management tools world.
ConnMan’s focus is a little different from that of the other major players in network
management space. The project’s focus is on managing Internet connection settings in
embedded devices running Linux.
ConnMan is especially suited for embedded and low-powered devices because of
its purported small footprint, which means that it tries to use as few system resources
as possible.
Like the other network management tools, ConnMan uses a plug-in architecture so
that it can be easily extended to support new and emerging networking technologies
and protocols.
Note  Keep in mind that ConnMan’s stated focus is the same type of modest focus (or ambitions)
that everything starts with. There are too many real-life examples of companies or projects that start off
as small with a niche focus and end up everywhere! So don’t be surprised if you start seeing ConnMan
replacing established applications such as nm on the desktop platforms in the coming years.
Good Ol’ CLI
When all the nice GUI network management tools fail, there will always be the CLI. It
was hinted earlier that the GUI network management tools rely on the command line
tools in one form or another in their back-ends, so having a good understanding of how
to use the CLI tools is never a waste and can come in handy in many situations—such
as when you’re troubleshooting or debugging wireless connectivity issues, for testing
purposes, or even when the GUI tools are simply not available.
Some of the CLI tools that can be used for configuring wireless network interface in
FOSS systems are described in the following sections.

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iwconfig
iwconfig is used for configuring the wireless characteristics of wireless network
interfaces. It can be used for querying and manipulating Open System Interconnection
(OSI) layer 1 and layer 2 properties of network devices.
Note  See the “Wireless Extensions API” section earlier in the chapter for more information.
The syntax for iwconfig is shown in here:
Usage: iwconfig [interface]
interface essid {NNN|any|on|off}
interface mode {managed|ad-hoc|master|...}
interface freq N.NNN[k|M|G]
interface channel N
interface bit {N[k|M|G]|auto|fixed}
interface rate {N[k|M|G]|auto|fixed}
interface enc {NNNN-NNNN|off}
interface key {NNNN-NNNN|off}
interface power {period N|timeout N|saving N|off}
interface nickname NNN
interface nwid {NN|on|off}
interface ap {N|off|auto}
interface txpower {NmW|NdBm|off|auto}
interface sens N
interface retry {limit N|lifetime N}
interface rts {N|auto|fixed|off}
interface frag {N|auto|fixed|off}
interface modulation {11g|11a|CCK|OFDMg|...}
To learn more about the syntax and various options that can be used with the
iwconfig command, consult built-in help system (often referred to as the “man
page”). To see more documentation about iwconfig, type the following command at
the shell prompt:
man iwconfig
The functionality provided by the iwconfig command is being replaced by the iw
command, discussed next.
iw
This is the new command line wireless configuration utility for wireless devices in
FOSS systems. It makes use of the nl80211 interface of the new mac80211 wireless API
in the Linux kernel.
Like iwconfig, iw can also be used for querying and manipulating OSI Physical
layer (layer 1) and the Data Link layer (layer 2) properties of network devices.

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The syntax for using iw and some of the common options are shown here:
Usage: iw [COMMAND]
Where COMMAND can be any combination of the following:
Commands:
event [-t] [-f]
phy
list
dev <devname> set channel <channel> [HT20|HT40+|HT40-]
dev <devname> set freq <freq> [HT20|HT40+|HT40-]
dev <devname> set type <type>
dev <devname> set meshid <meshid>
dev <devname> info
dev <devname> del
dev <devname> interface add <name> type <type>
dev <devname> ibss join <SSID> <freq in MHz> [fixed-freq] [<fixed bssid>]
dev <devname> ibss leave
dev <devname> station dump
dev <devname> station set <MAC address> plink_action <open|block>
dev <devname> station del <MAC address>
dev <devname> station get <MAC address>
dev <devname> get mesh_param <param>
dev <devname> set mesh_param <param> <value>
dev <devname> scan [-u] [freq <freq>*] [ssid <ssid>*|passive]
dev <devname> scan dump [-u]
dev <devname> scan trigger [freq <freq>*] [ssid <ssid>*|passive]
reg get
reg set <ISO/IEC 3166-1 alpha2>
Table 15-2 shows some sample iw command line options and usage.
To learn more about the syntax and various options that can be used with the iw
command, consult the man page. To see more documentation about the iw command,
type the following at the shell prompt:
man iw
wpa_supplicant
This is the Swiss army knife equivalent of a wireless security configuration tool in
the FOSS world. It is also available on other OS platforms. Among other things, wpa_
supplicant can be used for configuring the authentication, authorization, association,
and encryption parameters of a wireless STA.
Specifically, it is a Wi-Fi Protected Access (WPA) client and an IEEE 802.1X supplicant.
It is responsible for negotiating encryption keys and parameters with an authenticator

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iw Command and Options
iw list
iw event
iw dev wlan0 station
dump
iw reg get
iw reg set <ISO/IEC
3166-1 alpha2>
Description
List all wireless devices and their capabilities.
Monitor wireless events from the kernel.
Useful when debugging authentication,
deauthentication, association, and
disassociation issues.
Show wireless station statistic information for
the wireless interface wlan0.
Display the kernel’s current regulatory domain
information.
Change the current regulatory domain.
Table 15-2.  iw Toolset
(such as a wireless access point) and is also responsible for negotiating Extensible
Authentication Protocol (EAP) authentication parameters with the authentication
server (such as a RADIUS server). To be pedantic, wpa_supplicant implements the
WPA Supplicant component of the IEEE 802.11i standard.
The syntax and options that can be used with the wpa_supplicant program are
shown here:
Usage: wpa_supplicant [OPTIONS]
Where some of the common OPTIONS can be any combination of the following:
-B = run daemon in the background
-c = Configuration file
-i = wireless interface name
-d = increase debugging verbosity (-dd even more)
-D = driver name (can be multiple drivers: nl80211,wext)
-f = log output to debug file instead of stdout
-g = global ctrl_interface
-K = include keys (passwords, etc.) in debug output
-t = include timestamp in debug messages
-p = driver parameters
-P = PID file
-q = decrease debugging verbosity (-qq even less)
-u = enable DBus control interface
-N = start describing new interface

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To learn more about the syntax and various options that can be used with the wpa_
supplicant command, consult the man page. To see more documentation about the
wpa_supplicant command, type the following command at the shell prompt:
man wpa_supplicant
wpa_passphrase
This utility is an accoutrement to the wpa_supplicant toolkit. wpa_passphrase takes an
ASCII input and generates WPA preshared key, using the supplied service set identifier
(SSID) as the salt (random information added to a password to make extracting the
password more difficult).
Wireless clients use the resulting key to encrypt the network traffic.
The output generated by wpa_passphrase can be used to create an important stanza
in wpa_supplicant’s main configuration file (wpa_supplicant.conf). This stanza is used
to begin new wireless network configurations.
The syntax and options for wpa_passphrase are straightforward:
wpa_passphrase usage:
wpa_passphrase <ssid> [passphrase]
For example, given a passphrase of “sample-passphrase” and an SSID of “sample-
ssid,” we can use wpa_passphrase to generate a preshared key and a wireless network
configuration stanza like the one here:
$ wpa_passphrase sample-ssid sample-passphrase
network={
ssid="sample-ssid"
#psk="sample-passphrase"
psk=531c39e23b7791bc6fd02eb1376f34d77de09b827a167c676f47f6a0b5a4d957
}
To learn more about the syntax and various options that can be used with the wpa_
passphrase command, consult the man page. To see more documentation about the
wpa_passphrase command, type the following at the shell prompt:
man wpa_passphrase
nm-tool
This is a nifty little tool. From its name, you can tell that it is related to the GUI
NetworkManager software.
nm-tool provides information and other wireless statistics about NetworkManager,
wireless devices, and wireless networks.
It does not accept any command line options and its usage is dead simple. At the
command line, just type this:
nm-tool

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ifconfig
ifconfig is used for configuring the network interfaces on Linux-based systems. It is
used for querying and manipulating OSI Network layer (layer 3) and the Transport
layer (layer 4) properties of network devices. ifconfig is therefore not used for
configuring the radio or IEEE 802.11 characteristics of wireless interfaces. That function
is left for iwconfig and iw to do.
Once the radio properties for a wireless adapter have been set up, ifconfig can
perform the relevant network protocol–level configurations. It can be used for setting
up protocol-level parameters such as the TCP/IP configuration for the wireless (or
wired) interface.
The following syntax and options can be used with ifconfig:
Usage: ifconfig device address [options]
Where device is the name of the Ethernet device (for instance, eth0), address is the
IP address you want to apply to the device, and options are one of the following:
Option
Up
Down
Arp
-arp
mtu value
netmask address
broadcast address
pointtopoint address
Description
Enables the device. This option is implicit.
Disables the device.
Enables this device to answer arp requests (default).
Disables this device from answering arp requests.
Sets the maximum transmission unit (MTU) of the device
to value. Under Ethernet, this defaults to 1500.
Sets the netmask to this interface to address. If a value
is not supplied, ifconfig calculates the netmask from
the class of the IP address. A class A address gets a
netmask of 255.0.0.0, class B gets 255.255.0.0, and class C
gets 255.255.255.0.
Sets the broadcast address to this interface to address.
If a value is not supplied, ifconfig calculates the
broadcast address from the class of the IP address in a
similar manner to netmask.
Sets up a point-to-point connection (PPP) where the
remote address is address.
To learn more about the syntax and various options that can be used with the
ifconfig command, consult built-in man page. To see more documentation about the
ifconfig command, type the following at the shell prompt:
man ifconfig

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ip
Another powerful program that can be used to manage network devices in Linux is
the ip program. This utility comes with the iproute software package, which contains
networking utilities (such as ip) that are designed to use the advanced networking
capabilities of the Linux kernel. The syntax for the ip utility is a little more terse and
less forgiving than that of the ifconfig utility.
ip is the preferred toolkit for configuring the network interfaces on newer Linux-
based systems. It provides similar functionality to that provided by ifconfig but is
much more powerful than ifconfig.
It is used for querying and manipulating OSI Network layer (layer 3) and Transport
layer (layer 4) properties of network devices.
ip does not concern itself with the radio or IEEE 802.11 characteristics of an
interface. That function is left for iwconfig and iw to do. Once the radio properties for
a wireless adapter have been set up, ip can perform the relevant network or transport
level configurations.
To learn more about the syntax and various options that can be used with the
ip command, consult built-in man page. To see more documentation about the ip
command, type the following at the shell prompt:
man ip
Ubuntu Wireless Client Configuration: nm
Ubuntu is one the most popular and highly regarded Linux-based distributions. It is
backed and sponsored by Canonical Ltd.
Ubuntu is a derivative of another popular Linux distribution called Debian. As in
other popular Linux-based distributions, Ubuntu is an amalgamation of numerous
open source projects and the Linux kernel.
We’ll configure a sample system running the Ubuntu OS to connect to one of the
WAPs that we configured in Chapter 12. Some of the relevant properties of the WAP
are listed in Tables 15-3, and Table 15-4 shows the properties of our Ubuntu client
acting as our wireless client STA as well as some of our configuration objectives.
1. Log into the Ubuntu system as a regular user.
2. Launch the NetworkManager GUI tool to set up the wireless interface using
any of these methods to open the Network Connections window shown in the
following illustration:
■■ Simultaneously press alt-f2 to launch the Run Application dialog box.
Type nm-connection-editor in the text box and click the Run button.
■■ Locate the NetworkManager system tray applet in the top-right corner of
the desktop. Right-click the icon and select the Edit Connections option.

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Specification
Host name
SSID
Supported ciphers and authentication
Encryption key or passphrase
Wireless PHYs supported
Value
wap-1
area-1
WEP 64 / 128 bits
WPA-Personal / TKIP
WPA-Personal / CCMP
WPA-Enterprise / TKIP
WPA2-Personal / TKIP
WPA2-Personal / CCMP
WPA2-Enterprise / CCM
$never-never-land1$
802.11b, 802.11g, 802.11a, 802.11n
Table 15-3.  WAP Specifications
Specification
Host name
Operating system
Wireless card vendor and type
Wireless card driver
Supported ciphers and authentication
Compatible/optimal/suitable cipher
and authentication
Supported IEEE 802.11 standards
Compatible/optimal/suitable IEEE
802.11 standard
Network name or SSID
Value
foss01
Ubuntu Linux
Atheros
ath5k
WEP
WPA-Personal / TKIP
WPA-Personal / CCMP
WPA-Enterprise / TKIP
WPA2-Personal / TKIP
WPA2-Personal / CCMP
WPA2-Enterprise / CCMP
WPA2-Personal / CCMP
802.11b, 802.11g, 802.11a, 802.11n
802.11n
area-1
Table 15-4.  Ubuntu Client Wireless Specifications

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■■ Click System in the Main Menu area located in the top-left corner of the
desktop. Select Preferences and click Network Connections in the program
group.
3. Click the Wireless tab in the Network Connections window.
4. Click the Add button. A new dialog box will appear, where you can set up the
parameters for connecting to the wireless network.
5. Complete the fields with the information from Tables 15-3 and 15-4 so that the
completed screen resembles this:

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6. Click the Wireless Security tab. Complete the fields with the information in
Tables 15-3 and 15-4 so that the completed screen resembles this:
7. Accept the default settings in the IPv4 Settings and IPv6 Settings tabs.
8. Click the Apply button.
9. The passphrase (secret key) that was entered in step 6 is stored in a keyring so
that the system remembers it for you in the future. A keyring dialog window
might open, prompting you about allowing the NetworkManager applet access
to the newly created Wireless network. Click Always Allow.
10. The NetworkManager applet will immediately attempt to connect to the WAP
using the parameters just supplied. And if all goes well, you should see a
brief notification message (shown next) in the upper-right area of the desktop,
informing you that the connection to area-1 has been established.

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11. The ensuring Network Connections configuration window will resemble the
one shown next. Click the Close button to exit the NetworkManager program.
Tip  The NetworkManager has a nifty little applet in the upper-right area of the system tray (see step 2).
  Clicking this applet can provide useful information, such as a quick visual indication of radio signal
strength, the wireless network name to which the system is currently connected, and other wireless
networks that the Wi-Fi adapter detects in the vicinity.
  Figure 15-1 shows an example of some of the information that the system tray applet displays on
our sample system.
Figure 15-1.  Information displayed by the system tray applet

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Generic Linux Wireless Client Configuration: CLI
Here we’ll configure a sample system running the Ubuntu OS to connect to one of the
WAPs we configured in Chapter 12.
Some of the relevant properties of the WAP are shown in Table 15-3. Table 15-4
shows the properties of our Linux client acting as our wireless client STA, as well as
some of our configuration objectives.
The configuration will be using the CLI of our sample system. We will use some
of the utilities and programs discussed earlier—iw, wpa_supplicant, and wpa_
passphrase.
Note  The commands and utilities we’ll use for the command line configurations will need to be
executed from a shell prompt or a terminal. We therefore need a terminal program or a terminal
emulator program of some sort. As with everything FOSS, you have several options, some of which
might already be installed by default. Some of the popular terminal program choices are xterm,
gnome-terminal, and konsole. We will use xterm on our sample system.
  In addition, the following procedures are lengthy, because extra information has been interspersed
with the steps in the process. This extra information might prove useful to extra-curious readers.
The little extras are completely optional and should not affect our final objective. The information is
marked with an [OPTIONAL] tag. Feel free to skip steps that begin with [OPTIONAL] if you are so
inclined.
PHY and MAC Layer Configuration: CLI
Let’s start by configuring the PHY and MAC layers using the CLI:
1. Log into the Linux system as a regular user.
2. Press alt-f2 keys to launch the Run Application dialog box.
3. Type xterm in the text box and click the Run button. A xterm window similar
to the following will appear. This is our first terminal window.
4. Some of the commands we will need to configure the wireless settings
manually need to be executed by a user with administrative privileges on the
system—such as the root user. If you are already logged into the system as the
root user, you can ignore this step and jump to step 5.

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On Debian-based systems such as Ubuntu, you can temporarily become the
root user by typing (the command to type begins after the $):
username@foss01:~$ sudo su -
Then enter the appropriate password when prompted.
On Red Hat–based systems (such as Fedora, Red Hat Enterprise Linux [RHEL],
openSUSE, and Centos), you can temporarily become the root user by typing
this command (shown in boldface):
username@foss01:~$ su -
Enter the appropriate password when prompted.
5. The NetworkManager applet is usually running quietly in the background to
help manage the network devices in newer Linux distributions. Since we want
to do things manually here, we will temporarily stop the nm service so that it
does not get in our way. To stop the service, type the following:
root@foss01:~$ service network-manager stop
6. [OPTIONAL] We need to create a simple configuration file for the wpa_
supplicant utility, which will contain the name of the wireless network with
which we want to associate, as well as the secret key for the WPA2-PSK
encryption type we are using. We will use wpa_passphrase to generate a
sample output. The output will be printed directly to the terminal. This is just a
test run. Type the text shown in boldface:
root@foss01:~$ wpa_passphrase area-1 '$never-never-land1$'
network={
ssid="area-1"
#psk="$never-never-land1$"
psk=6ababa9040d5f450e0ad7221febead68a3008863fac6e9eee364478a4
615c6ec
}
7. The test output looks fine, so we can go ahead and write the output directly
to our sample configuration file. The file will be named area-1-wpa.conf. Type
this:
root@foss01:~$ wpa_passphrase area-1 '$never-never-land1$' >
area-1-wpa.conf
We are almost ready to connect to our WAP.
8. [OPTIONAL] Before we connect, let’s find a way to monitor some of the stuff
going on in the background when a wireless STA connects to an access point
(AP). To do this, we launch another terminal and run different commands there
to watch what happens.

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9. [OPTIONAL] Repeat steps 2 and 3 to launch a new xterm window—our
second terminal window. Arrange the first and second xterm windows on your
screen so that you can view them side-by-side without one overlapping the
other.
10. [OPTIONAL] We will use the iw command with its event option to display
wireless events in real time as they are generated by the wireless adapter driver
and other changes.
On Debian/Ubuntu systems, install iw if you don’t have it installed already, by
typing
sudo apt-get install iw
On Red Hat–based systems, install iw by typing yum install iw.
This command should be typed in the second xterm window:
root@foss01:~$ iw event
11. Use wpa_supplicant to connect to the WAP over the interface wlan0, using the
configuration file we created in step 7. Type this:
root@foss01:~$ wpa_supplicant -Dnl80211 -iwlan0 -c ./area-1-wpa
.conf
CTRL-EVENT-SCAN-RESULTS
WPS-AP-AVAILABLE
Trying to associate with 00:14:6c:dd:4a:1c (SSID='area-1'
freq=2442 MHz)
Associated with 00:14:6c:dd:4a:1c
WPA: Key negotiation completed with 00:14:6c:dd:4a:1c [PTK=TKIP
GTK=TKIP]
CTRL-EVENT-CONNECTED - Connection to 00:14:6c:dd:4a:1c completed
(auth) [id=0 id_str=]
12. [OPTIONAL] The console of the second xterm window will be updated as new
wireless events are detected. It might have an output similar to this on our
sample system:
root@foss01:~$ iw event
wlan0 (phy #0): scan finished
wlan0 (phy #0): auth 00:14:6c:dd:4a:1c -> 00:16:ce:6a:2e:ba
status: 0: Successful
wlan0 (phy #0): assoc 00:14:6c:dd:4a:1c -> 00:16:ce:6a:2e:ba
status: 0: Successful
Our Linux-based wireless STA should now be properly authenticated and
associated with the WAP. This means that everything is okay at the PHY and
MAC layers between the STA and the AP. This is the same as wireless or radio
link.

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Network and Transport Configuration: CLI
Now we’ll deal with the network and transport layers of the communication link so
that we can actually do something useful with it:
1. Repeat steps 2 and 3 (in the “PHY and MAC Layer Configuration: CLI” section)
to launch a new xterm window. This will be our third xterm window. Arrange
the first, second, and third xterm windows on your screen so that you can view
them without one overlapping another.
This part of the configuration process should be easy, because, thankfully, we
have a Dynamic Host Configuration Protocol (DHCP) server running on wap-1
(the AP). We configured the DHCP server service earlier on in Chapter 12 when
we configured our infrastructure devices.
2. Most FOSS distributions ship with DHCP client functionality. One popular
FOSS implementation of DHCP client software is the dhclient, which is used
for configuring interfaces using DHCP. Run the dhclient utility with the name
of the wireless interface (wlan0, in our case) as the only argument. Type this:
root@foss01:~$ dhclient wlan0
Internet Systems Consortium DHCP Client
For info, please visit http://www.isc.org/sw/dhcp/
Listening on LPF/wlan0/00:16:ce:6a:2e:ba
Sending on LPF/wlan0/00:16:ce:6a:2e:ba
Sending on Socket/fallback
DHCPDISCOVER on wlan0 to 255.255.255.255 port 67 interval 4
DHCPOFFER of 172.16.1.3 from 172.16.1.254
DHCPREQUEST of 172.16.1.3 on wlan0 to 255.255.255.255 port 67
DHCPACK of 172.16.1.3 from 172.16.1.254
bound to 172.16.1.3 -- renewal in 39788 seconds.
According to the output, it looks like we are good to go. We were able to get
an IP address lease from wap-1. The new IP address of the Linux client STA is
172.16.1.3. And the IP address of the DHCP server (wap-1) is 172.16.1.254.
3. Let’s do some simple diagnostic tests and gather some statistics for the wireless
connection to make sure that we have IP layer connectivity with wap-1. Type
this:
root@foss01:~$ ping -c 2 172.16.1.254
PING 172.16.1.254 (172.16.1.254) 56(84) bytes of data.
64 bytes from 172.16.1.254: icmp_seq=1 ttl=64 time=1.18 ms
64 bytes from 172.16.1.254: icmp_seq=2 ttl=64 time=4.72 ms
--- 172.16.1.254 ping statistics ---
2 packets transmitted, 2 received, 0% packet loss, time 1001ms
rtt min/avg/max/mdev = 1.189/2.956/4.724/1.768 ms
Looks good.

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4. Now let’s view some of the interface statistics. Type this:
root@foss01:~$ iw dev wlan0 station
Station 00:14:6c:dd:4a:1c (on wlan0)
inactive time: 3572 ms
rx bytes:
3534066
rx packets:
27233
tx bytes:
163800
tx packets:
1281
signal:
-12 dBm
tx bitrate:
54.0 MBit/s
dump
5. Display the PHY capabilities of the wireless devices:
root@foss01:~$ iw list
Wiphy phy0
Band 1:
Frequencies:
* 2412 MHz [1] (20.0 dBm)
* 2417 MHz [2] (20.0 dBm)
...<TRUNCATED>....
* 2484 MHz [14] (20.0 dBm)
(passive scanning)
Bitrates:
* 1.0 Mbps
* 2.0 Mbps (short preamble supported)
...<TRUNCATED>....
* 54.0 Mbps
Band 2:
Frequencies:
* 5180 MHz [36] (30.0 dBm)
(passive scanning, no IBSS)
* 5200 MHz [40] (30.0 dBm)
(passive scanning, no IBSS)
...<TRUNCATED>....
Bitrates:
* 6.0 Mbps
* 9.0 Mbps
...<TRUNCATED>....
* 48.0 Mbps

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6. Display the PHY layer and MAC layer information about the wireless interface:
root@foss01:~$ iw dev wlan0 scan dump
BSS 00:14:6c:dd:4a:1c (on wlan0)
TSF: 9180742729 usec (0d, 02:33:00)
freq: 2422
beacon interval: 100
capability: ESS Privacy ShortPreamble ShortSlotTime
(0x0431)
signal: -23.00 dBm
SSID: area-1
Supported rates: 1.0* 2.0* 5.5* 11.0* 6.0 9.0 12.0 18.0
DS Paramater set: channel 3
ERP: <no flags>
Extended supported rates: 24.0 36.0 48.0 54.0
WPA:
* Version: 1
* Group cipher: TKIP
* Pairwise ciphers: TKIP
* Authentication suites: PSK
WMM: parameter: 01 80 00 03 a4 00 00 27 a4 00 00 42 43 5e
00 62 32 2f 00
That’s it.
Using Propriety Drivers or Firmware for Wireless Adapters
The following procedures show how a sample Ubuntu system deals with
detecting and installing propriety software that cannot be legally packaged
with the OS. I assume that the system used here has a connection to the Internet
through some interface other than the wireless interface, since the wireless
interface is currently disabled due to lack of proper driver or firmware.
1. While logged into the system, make sure that the system has a connection
to the Internet via some other means, such as a wired connection
(Ethernet).
2. Press alt-f2 to launch the Run Application dialog box.
3. Type jockey-gtk in the text box and click the Run button.
4. The utility will launch and start by searching for any relevant hardware
on the system that may need proprietary drivers or firmware to function.
(Continued)

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Our sample system uses a wireless network adapter with a Broadcom
chipset, which needs some proprietary software to function. A hardware
drivers screen appears:
Select the appropriate driver for your hardware from the list, and then
click the Activate button. For our sample system, we choose the open
source B43 driver combined with the closed source firmware. The b43-
fwcutter utility will take care of the proprietary firmware for us.
5. A dialog box might open, prompting you to authenticate to the system
before being permitted to perform the privileged operation. Enter the
necessary password in the Password text box and click Authenticate.
6. The program will proceed to downloading and installing the necessary
software for the hardware. After completion, the hardware drivers
screen will change to reflect the fact that proprietary software is in use

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on the system. The screen will resemble the one shown next. Click the
Close button to exit the application.
7. For good measure, you should probably reboot the system at this time.
After the system has booted, you should be able to use the newly
activated wireless interface. You can now carry out the procedures
described in the “Ubuntu Wireless Client Configuration” section.
Wireless Odds and Ends in FOSS/Linux
As with the other mainstream OS platforms discussed so far in this book, FOSS-based
systems have their own implementations of various new technologies in the wireless
networking world.
As mentioned in the preceding chapters, every OS vendor tries to be the first to
implement support for the latest wireless standards and technologies. Other vendors
wait for the standards or technologies to become mature before incorporating support
into their base OSs. Linux and FOSS–based systems are no exception.

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In general, and as a matter of fact, the FOSS community is on the bleeding edge of
new technologies, which has its advantages and disadvantages. One of the advantages
is that the FOSS community gets a chance to play with new toys before they are
released on other platforms. The community often also acts as a sort of proofing
ground (guinea pigs) for some of this new stuff. If the technology works well and is
determined to be useful, the mainstream OSs try to adopt it.
The disadvantage to living on the cutting edge of things is that you get what you
get. There are often no guarantees or warranties of any sort.
It should be clarified at this point that within the FOSS community, numerous
distributions (distros) target different users. This means that the different distros exhibit
different levels of conservativeness—some ship with very cutting edge technologies
and others ship with more conservative technologies.
Ad-Hoc Networks
Ad-hoc networks are wireless networks that do not make use of traditional infrastructure
devices (such as APs) for connectivity among wireless stations (STAs).
Systems connected to an ad-hoc network do not automatically have access to the
Internet via the host. An ad-hoc network is used only to facilitate network communication
between members of the network. These systems are on their own little islands.
Ad-hoc networks are not covered by any official standards, but they are very popular.
Different OS platforms have their own implementations with different features.
Security in ad-hoc wireless networks is usually a toss of the coin. This is even more
true when the ad-hoc networks consists of STAs running different OSs. Unfortunately,
the best compatibility mode when dealing with different platforms is to disable security
completely.
Setting up an ad-hoc network on FOSS platforms can be a dead easy process. We’ll
walk through setting up a simple ad-hoc network using an Ubuntu Linux–based
distribution. The ad-hoc network will be created with the configuration settings in
Table 15-5.
Specification
SSID/ network name
Channel
Passphrase
Wireless security
Table 15-5.  Ad-Hoc Network Settings
Value
ad-hoc-linux
Accept the default value
128-linux-adhoc
WEP 128-bits

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Perform the following steps on the system that will be initiating and hosting the
ad-hoc network—aka, the source:
1. Log into the Ubuntu system as a regular user.
2. Locate the NetworkManager system tray applet in the top-right corner of the
desktop. Click the icon and select the Create New Wireless Network... option.
A New Wireless Network dialog box will appear, which looks similar to this:
3. Complete the fields of the dialog box with the information from Table 15-4. The
completed screen will look like this:
4. Click the Create button.
5. The NetworkManager applet will immediately attempt to enable the new
ad-hoc network on the local system. If all goes well, you should see a brief
message in the upper-right area of the desktop informing you that the ad-hoc-
linux connection has been established.
6. The ad-hoc network with the SSID of ad-hoc-linux will now be active and
ready for other wireless clients to join it.

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dnsmasq, iptables, dhcp, and dns in Ad-Hoc Networks
Several cool things happen “automagically” in the background whenever a
system is configured to host an ad-hoc network in a Linux-based system.
One of these things relies on the dnsmasq package (application), a caching
DNS proxy and DHCP server with a very small footprint. dnsmasq is installed
by default in recent versions of Ubuntu, but you can quickly install it on older
systems if necessary (using sudo apt-get install dnsmasq-base).
The program ships with a sensible set of defaults so that it just works without
any user input. For example, on an Ubuntu/Debian-based system, the following
is the default behavior of dnsmasq:
1. Assign the network interface of the host managing dnsmasq the IP
address of 10.42.43.1.
2. Assign DHCP address to clients in the range 10.42.43.10 to 10.42.43.100.
3. Assign the clients with a gateway address of 10.42.43.1.
These defaults mean that all stations connected to the ad-hoc network will
get assigned IP addresses in the range of 10.42.43.10 to 10.42.43.100, and the host
running the show will be assigned an IP address of 10.42.43.1. This is how the
systems on the ad-hoc network get their TCP/IP configuration. And the defaults
can be changed by explicitly running dnsmasq with a configuration file that
contains the desired parameters.
The second thing that happens is that the packet filter subsystem of the Linux
kernel gets activated. That subsystem is known as netfilter, and the utility that
manages that subsystem is known as iptables. iptables is used for managing
packet forwarding, routing, firewall, and packet logging functions in the Linux
kernel.
iptables can also have different front ends (GUI, scripts) to make it easier to
use. One such front end is the Uncomplicated Firewall (ufw) in Ubuntu/Debian-
based systems.
iptables is used to create simple firewall rules to protect the host managing the
ad-hoc network.
Once the ad-hoc network is disabled, the automatic firewall rules and other
settings created by dnsmasq are removed, and the dnsmasq daemon goes back
to sleep.

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Perform the following steps on the other systems that will join the ad-hoc network
(the target systems):
1. Use any wireless network management utility available on the system to locate
and connect to the ad-hoc network with the SSID of ad-hoc-linux.
■■ In other Linux-based systems, you can use nm, the command line, wicd, or
ConnMan.
■■ In Mac OS X systems, you can use the network preferences application.
■■ In Microsoft Windows systems, you can use the Manage Wireless
Networks Control Panel applet.
2. Supply the WEP passphrase from Table 15-5 when prompted for a password or
key to join the network.
If everything goes well, the system will be connected to the ad-hoc network and
will be able to communicate with other systems that are connected to the same ad-hoc
network.
Summary
The Linux OS is at the heart of most Free and Open Source Software (FOSS) distributions.
In this chapter, you learned about wireless hardware compatibility issues on FOSS
platforms, and you learned about Linux wireless drivers and the different Linux
wireless APIs. You learned how to use GUI and command line tools to set up and
configure hardware and firmware for wireless Linux-based client systems. You also
learned how to set up an ad-hoc wireless network for Linux clients.
Relative to the preceding chapters discussing the other mainstream platforms
(Windows and Apple OS X), a lot of extra information and detail was provided in this
chapter. The very nature of FOSS automatically gave us the choice, the resources, and
the tools to communicate this level of detail.

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Plan, Design, Survey,
and Deploy
267

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Key Skills and Concepts
■■ Review and reveal the wireless network administrator’s Quad-W rule of
thumb.
■■ Understand the importance of planning when designing wireless networks.
■■ Learn the art and importance of wireless site surveys.
■■ Review the special considerations for different wireless network deployment
scenarios.
Because some of what you’ll be reading about in this chapter will make sense only
after you’ve read the information in earlier chapters, we placed the cart before
the horse by setting up our infrastructure devices and connecting our wireless
client stations (STAs) to the network. In the real world, we should formally plan and
scope out our wireless network before throwing the hardware into it. So we will do
what we should have done four chapters ago here.
In the real world, before deploying hardware on a wireless network, a wireless
network administrator should follow the Quad-W (WWWW) rule of thumb. The
Quad-W rule is simple: wireless network planning, wireless site survey, wireless
network design, and wireless network deployment. We start by planning the network
using information gathered during the site survey. Certain elements and information
gathered from the site survey activities show up in the planning and designing stages.
As such, the site survey goes hand in hand with the planning and designing activities.
Next, the information garnered from the site survey is used to tweak and optimize the
network design. Finally, the actual deployment can begin.
The discussions in this chapter take a high-level view and include a few low-level
technical details of planning, designing, and deploying a wireless network.
Wireless Network Planning and Designing Considerations
A properly planned wireless network supported by a solid network design and
implementation process can help detect and prevent issues that can become a source of
headaches in the future. We’ll start by taking a look at network hardware.
Past, Present, and Future Hardware
The incredible growth and fast rate of development in today’s wireless industry
make it easy for wireless network administrators and users to end up with obsolete
or unsupported hardware before they know it. In some respects, this particular issue
is a little tricky to prevent, because nobody has a crystal ball to predict the future.

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But wireless network administrators can do a few things to help ensure that they
get the most out of their hardware purchases. Plan your network to accommodate
existing legacy hardware and technologies—within reason, of course. For example, it
doesn’t make any sense to force all the wireless stations on the network to run at IEEE
802.11 speeds just because one station does not support any of the IEEE 802.11 b, g,
or n standards. In this case, it would be best to bite the bullet and upgrade the single
legacy client to support the newer wireless PHYs so that all the clients can reap the
benefits of the newer PHY standards.
You should also plan to include the hardware and technologies available today.
This is a no-brainer, since you probably don’t have much of a choice in this regard.
Only hardware that is readily available can be used in deploying a wireless network.
Finally, you should plan to use the hardware and technologies that are currently
under development. These hardware and technologies will be adopted in the near
future. Consider, for example, the recently ratified IEEE 802.11n standard. This
standard had been in the draft stage for a long time, but hardware vendors were
already manufacturing numerous products that supported the draft standard for
several years before its release.
In this case, it would have been quite prudent and safe to assume that the IEEE
802.11n would be the wireless LAN standard of the future and plan accordingly.
Practical and prudent planning in this case would ensure that any new wireless
equipment acquisitions had some support for the draft standard, or at least an easy,
built-in upgrade path to the standard.
Interoperability and Incompatibility Issues
Before recommending a bunch of expensive infrastructure hardware for purchase, a
wireless network administrator must make sure that existing client hardware will work
properly with the new hardware to avoid interoperability and incompatibility issues.
These issues can occur in hardware products whose manufacturers do not design and
build their hardware to conform to universally accepted standards. Original equipment
manufacturers (OEMs) sometimes do not fully adhere to standards in their product
designs, hoping to gain market advantages over their competition with “innovative”
unique designs.
Consider, for example, a wireless OEM that advertises a turbo-super-duper operation
mode that promises never-before-seen WLAN speeds. The devices are able to achieve
these speed improvements through nonstandards-based and proprietary means. The
effect of this, however, is that products created by other OEMs that need to interoperate
with the turbo-super-duper hardware in your network will be unable to do so, because
they don’t share the same “secret” design specs that allow this. Another way of
explaining this is that some extended or nonstandard operating modes are often only
achievable when pairing with or using equipment from the same vendor. As a result,
you’re forced to use only one OEM’s equipment throughout your wireless network—
you’ll need the turbo-super-duper wireless client adapter made by ACME Corp. to go
with the turbo-super-duper wireless access point (WAP), also made by ACME Corp.

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Data Throughput
A properly executed site survey (discussed shortly) can help you plan against issues
that affect the overall throughputs on a wireless network. Poor data throughputs, in
user terms, is usually described as a “slow network.” Proper wireless network planning
and designing will take into consideration the applications, data, and other uses of a
wireless network. You can then use this information to design a wireless network that
will provide the best throughputs to support various use cases.
The planning and design might also determine, for example, that some users,
groups, or departments need to be segmented from others. They can also determine
that certain areas need more stringent security requirements than others, or perhaps
help you realize that a wired solution will better serve the users’ needs in certain parts
of the network.
Network Reliability
Network reliability is another important metric by which users measure a network.
You can be sure that the users or clients of the network will let you (and upper
management) know if the network is flaky and unreliable. Unreliable and erratically
behaving networks are not only an annoyance, but they impact user productivity.
Proper planning before deploying a wireless network can help you mitigate issues
of unreliability and other unpredictable behaviors on the network. For example, it
can be easy to overlook the effects of the locations or positions of physical objects on
wireless network—such as furniture, trees, walls, plumbing, and so on. For this reason,
the results of a wireless site survey of an empty office space will likely be different from
a site survey of the same space inhabited with cubicles and furniture.
In shared spaces or buildings with neighbors, wireless equipment can also affect the
reliability of a wireless network. Even though you may not have any control over the
operation of radio equipment of other offices, you can at least plan for the optimization
of equipment under your control. A site survey can help you spot such issues ahead of
the actual deployment of the wireless network.
Estimating Hardware Requirements
It’s important that you neither underestimate or overestimate the hardware requirements
for your wireless network.
Overestimating hardware requirements can mean budgeting or dedicating too many
resources to meet simple needs—recommending an enterprise wireless LAN controller
with a 10 GB/s backplane for a two-man bookkeeping business, for example, would be
considered overkill. Deploying numerous access points (APs) in a small space when it
makes more sense to use a single, well-positioned AP is another example.
On the other hand, by underestimating hardware requirements, you may save a
few dollars in hardware expenditures today, but you may find yourself wishing you’d
spent more to get more appropriate equipment further down the road. Although saving
money makes upper management happy, it is more important that you choose the right
hardware to meet the needs of the wireless network.

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For example, planning a network for ten users and purchasing equipment that is
designed to serve exactly ten users should be considered cutting things too close. You
should instead plan for infrastructure equipment that would easily scale to at least 20
users. Another example: You wouldn’t use a single WAP to provide coverage for a large
area when it is makes more sense to deploy multiple APs or repeaters to extend the
network’s reach.
Note  There are no equations or formulas to help you arrive at the perfect network plan; it’s
mostly about common sense.
Site Survey
A good site survey will yield vital information that will aid in designing and planning
a successful wireless network. Site surveys can help in determining cell coverage,
capacity planning, network documentation, benchmarking, and accessing user
requirements. All these activities impact the final wireless network deployment directly
or indirectly.
Note  Cell coverage refers to the useful area that a WAP’s radio waves can cover. Cell coverage
is useful information when you’re determining the best locations for wireless equipment to meet
users’ needs.
The site survey generally has two facets. The first is nontechnical and involves fact-
finding and paper-pushing processes. It also involves accessing actual user requirements.
The second aspect of a site survey is more technical and physical in nature. It
can involve taking measurements, assessing the radio propagation properties of the
physical environment, and other similar requirements.
Site Survey Metrics
The technical aspects of a proper site survey involves walking around the site and
collecting and recording radio frequency (RF) and data metrics at different points in the
site—such as the received signal strength (RSS), data rates, and signal-to-noise ratio (SNR).
The RSS metric affects the overall coverage in the site. The lower the value of
the RSS, the farther the network will reach. A -65dBm (decibels below 1 milliwatt) is
commonly regarded as a decent value for the RSS at the edges of a wireless network.
The SNR measures the difference between the useful RF signals and the undesirable
(and inevitable) background noise. The SNR directly affects the data rates achievable
on the wireless network. In a good SNR, more of the useful signal is available relative
to the noise signal. So a higher SNR implies that effects of the noise signals are less
noticeable. In real-world applications, an SNR value of 35dB (decibels) is better than
a SNR value of, say, 10dB.
Network data rates reflect the actual data throughputs achievable on the network.

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About RF Interference
You’ll spend a good chunk of time gathering different metrics during your site
survey. Many of these metrics are used eventually in trying to reduce interference
to a bare minimum and in determining optimal network configurations.
Every wireless network will encounter many sources of interference, which
can be cordless phones, neighboring wireless networks, fluorescent lights, and
microwave ovens, for example. Their effects range from the benign to major.
Regardless of the source of the interference, it’s an undesirable factor in a wireless
network deployment.
RF interference in a wireless network has many side effects. Slow network
performance is one example. Because the transmission medium in wireless
networks is a shared medium, there needs to be a way to police the medium so
that all the wireless clients get their fair share of access. Radio interference can
disrupt this policing mechanism and slow down legitimate traffic on the network.
The source of the interference effectively hogs the medium, which prevents other
devices from using it in a timely fashion. This is one of the causes of what users
perceive as a slow wireless network.
It is also possible that, by some freak chance, excessive RF noise can lead to
corruption of the data being transmitted over a wireless network. This corruption
means that the built-in checks that wireless STAs use to confirm receipt of packets
will fail, and the sending STA may be forced to resend the data several times
before the receiving STA finally acknowledges it (provided it isn’t corrupted).
This inevitably leads to unnecessary retransmissions, which can slow down the
network.
Site Survey Tools
It is sometimes wrongly assumed that a site survey can be performed only with certain
specialized equipment and by special individuals and firms. This assumption is also
one of the chief reasons why some people don’t bother conducting surveys.
It is true that expensive and specialized equipment is available for performing site
surveys, and this equipment will do an excellent job. For example, a spectrum analyzer
or an oscilloscope can cost $40,000 and is used to measure the frequency, bandwidth,
noise, and distortion characteristics of RF circuitry.
But if you don’t own your own personal spectrum analyzer, you can choose from
among many other tools that can be used to perform a site survey on the cheap.
With a dose of common sense and commodity hardware and software, you can
perform a site survey that will not break the bank. A side benefit of this low-budget
approach is that you can use the same (or similar) hardware that will be used in the
final network deployment.

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Following are some of the tools you’ll need to perform a basic site survey for an
IEEE 802.11–based WLAN:
■■ Laptop or other portable 802.11-capable device
■■ A decent wireless adapter for the laptop or portable device
■■ Some kind of software to show display wireless RSS on the laptop (however, if
your specific software or utility does not show the RSS value, see the sidebar
“RSS Alternatives”)
■■ An AP or two
■■ Two to three different antenna types that can attach to the AP and/or wireless
adapter on the laptop
■■ A tape measure or a laser-based measuring tool
■■ Site map or floor plan—make a sketch of the floor plan if you need one
■■ A ladder
RSS Alternatives
Any software utility that helps you manage the wireless properties of your
wireless interface will have some way of displaying and expressing the signal
strength. This information is often displayed using a number of colored bars of
different heights—referred to as a “signal strength meter.”
Another common method is to express the quality of the wireless signal as a
percentage from 0 to 100 percent.
Let’s map our fancy RSS values to five little bars or their equivalent percentages
when the actual RSS values are not available. We’ll use the following conventions:
■■ When the wireless signal meter shows all five colored bars, we have an
excellent signal (or 100 percent signal strength) at the receiving station.
■■ When the wireless signal meter shows only three colored bars, we have
an average quality signal of around 50 percent or higher.
■■ We will map three bars or higher to RSS values greater than or equal to
-65dBm.
■■ Whenever the wireless signal meter shows only one colored bar, we have
a very low or poor signal.
Finally, when the wireless signal meter shows no colored bar, we have no
signal at all. At this point, you can replace all references to “-65dBs” when
conducting a real site survey with three bars or more. If your utility uses
percentages, substitute “-65dBs” with a signal strength of 50 percent or higher.

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The Actual Site Survey
The following procedure is admittedly a bit crude, but it will suffice in getting the job done.
One of the objectives of this sample site survey is to determine an optimal location for
the APs in the given space. For our purposes, the optimal location within the space provides
the best signal reception to the wireless clients while avoiding sources of interference.
Our second objective is to determine the number of APs that will provide good
coverage for our site.
First, let’s determine the optimal locations for the APs:
1. Power on the laptop.
2. If the laptop or other device does not have a built-in wireless adapter, install
the wireless adapter and any necessary software (such as drivers).
3. Attach the external antenna, if one exists.
4. Grab the floor plan for the space to be surveyed, or create a quick sketch of the floor
plan if one does not already exist. A sample floor plan is shown in Figure 16-1.
Microwave oven
G
H
I
F
J
A
B
K
L
Floor Plan
E
D
C
Figure 16-1.  Example floor plan

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5. Locate the approximate center of the entire space in the floor plan, and walk
over to that location. This is location D on our sample floor plan in Figure 16-1.
6. Power on and place an AP at that location. Make sure that all the wireless
security settings of the AP are disabled and that the radio is turned on.
7. Configure the laptop to associate with the WAP.
8. Because of the shape of our sample space, we’ll use a patch antenna at location
D. Attach the patch antenna to the first AP.
9. Starting at location D, we keep an eye on the wireless signal strength indicator
of the laptop and walk back and forth with the laptop in the directions of A,
B, C, E, F, G, H, I, and J. We stop walking in each direction after the signal
strength drops down to -65dBm.
10. During our sample survey, the -65dBm spot maps perfectly to the following
locations on the floor plan: A, B, C, E, and J.
11. Let’s rename these exact spots (A, B, C, E, and J) to D_end_A, D_end_B, D_
end_C, D_end_E, and D_end_J, respectively (see Figure 16-2). These locations
denote the outer boundaries of the RF coverage provided by the first AP. This
entire coverage area will be denoted as Cell_A.
12. We’ll also rename the location D to D_start.
13. D_start will be the proposed final location of the first AP.
14. These changes are reflected in Figure 16-2.
In some locations on our floor plan, there is still no RF reception. These locations
are denoted by F, G, H, and I in Figure 16-2. To find the optimal location for our second
AP, we start at one of the outer boundaries of Cell_A.
Specifically, we will start at location D_end_J (Figure 16-2).
1. With the laptop still in tow, walk to the location D_end_J and then walk to the
approximate center of F, G, H, D_end_J, and K. This center location is denoted
by I in Figure 16-2.
2. Power on and place the second AP in location I. Make sure that all the wireless
security settings of the AP are disabled and that the radio is turned on.
Configure the laptop to associate with the second WAP.
3. Because of the shape of our sample space (from the perspective of location I),
we’ll use an omnidirectional antenna at location I. Attach the omnidirectional
antenna to the second AP.
4. Starting at location I, keep an eye on the wireless signal strength indicator of
the laptop and walk back and forth with the laptop in the directions of E, F, G,
H, D_end_J, and K. Stop walking in those directions when the signal strength
drops down to -65dBm.

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Microwave oven
G
H
I
F
D_end_ J
D_end_A
K
L
Cell_A
D_end_B
D_end_E
D_start
Patch antenna
First access point
D_end_C
Figure 16-2.  First AP location
5. During our sample survey, the -65dBm spot maps perfectly to locations E, F,
G, H, and K on the original floor plan. Let’s rename locations F, G, H, and K
to I_end_F, I_end_G, I_end_H, and I_end_K, respectively. These locations will
denote the outer boundaries of the RF coverage provided by the second AP.
This entire coverage area will be denoted as Cell_B (Figure 16-3).
6. We’ll also rename location I to I_start, which will be the proposed final location
of the second AP. These changes are also reflected in Figure 16-3.
And that’s it. We now have RF coverage at all locations of our original floor plan.
We were able to do this using only two APs.
The information gathered during this procedure can now be incorporated into the
planning and designing processes.
Note  We could have probably gotten away with locating our second AP in location G of the floor
plan in Figure 16-1, with a directional antenna at that location. We didn’t use location G, however,
because of the industrial microwave oven located nearby.

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I_end_G
I_end_F
Microwave oven
I_end_H
I_start
Second AP
using omnidirectional
antenna
Cell_B
D_end_ J
I_end_K
D_end_A
L
D_end_B
Cell_A
D_end_E
D_start
Patch antenna
Figure 16-3.  Second AP location
First AP
D_end_C
Note  Admittedly, the preceding site survey procedure was a bit tedious to follow because
the reader has to repeatedly refer back to the floor plan for cross referencing. But although the
site survey methodology was a bit crude, you should have gotten the general point of the whole
exercise. Also, it should be noted that other site survey experts might be able to find more optimal
positions for the access points.
Wireless Site Deployment Examples and Considerations
When you’re designing and deploying wireless networks—or any type of networks—
you should keep a few things in mind. Beyond the common underlying wireless
technology, wireless networks at different sites may have different characteristics, and

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these differences can be a result of the application for which the wireless network is
being used. Some examples are discussed in the following sections.
Hospitals
Hospital environments have numerous RF-based devices in place, such as sensor and
alert devices, which serve as lifesaving technologies. Their proper operation can be a
matter of life or death. Deploying wireless networks for data communications in hospital
environments can be a complicated endeavor. Wireless communications equipment
must not cause any interference with other medical equipment. The wireless network
administrator may have to go as far as ensuring that certain areas or rooms in the
hospital are completely shielded from RF waves from wireless networking equipment.
Airports
Airports offer a mixed bag of sometimes conflicting requirements when it comes to
wireless data communications deployments. On the one hand, an airport relies heavily
on radio-based communication equipment to communicate between aircrafts and the
airport control center (tower). And on the other hand, the airport also caters to the
needs of the numerous passengers waiting or in-transit, by providing them a way
to access the Internet. The most convenient and practical way to provide passengers
access to the Internet is unarguably wirelessly.
As a result of these conflicting requirements in an airport environment, careful
network segmentation techniques may have to be employed. This segmentation
may have physical and logical components. The physical component has to do with
minimizing radio interference between flight communication equipment and wireless
data communications equipment. The logical segmentation component has to do with
separating the public (passengers) network data traffic from the airport’s private data
communications traffic.
Because an airport has no easy way of predefining or prequalifying the type of
wireless hardware that its customers intend to use on its Wi-Fi network, network
planners may need to make compromises and support legacy protocols and legacy
wireless technologies to accommodate as many people as possible.
Some airports overcome some of these issues by contracting out the provisioning
and management of their public-facing wireless data networks to third parties that use
captive portals to provision the wireless clients (passengers). The provisioning function
of such captive portals takes care of authentication, authorization, and accounting
needs of the clients.
Retail Environments
Retail environments rely on a multitude of wireless communications technologies. Since
the dependence on these technologies is usually unavoidable in retail environments, the
wireless network administrator must take steps to make the best of a bad situation.

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Retail environments rely heavily on wireless bar code scanners, RFID readers,
cordless payment processing systems, wireless video surveillance cameras, and
demo wireless electronics that are for sale. Most of these gadgets operate in the same
unlicensed radio frequency bands used by wireless networking equipment. This all
makes for an excellent recipe for interference and general chaos.
A specific use case that is more troubling in retail environments regards point-
of-sale systems or payment processing systems that use airwaves that haven’t been
properly secured. It can be easy for the bad guys to capture interesting network traffic
that contains customers’ financial data.
Data throughputs and other bandwidth issues are not too much of a concern in retail
environments because of the nature of the data being sent back and forth. Handheld
scanners, for example, typically transmit only short bursts of data intermittently and do
not occupy the RF spectrum for long periods.
High Security Areas
Examples of high security areas are banking and other financial institutions, government
agencies, and private institutions that deal in sensitive areas (energy, health care,
transportation, or defense, for example).
Let’s start off with a simple advisory list:
■■ The Wired Equivalent Privacy (WEP) is broken.
■■ The WPA is compromised.
■■ The WPA2 will someday be compromised.
■■ WPA3, WPA4, …WPA-unbreakable-edition-version-100 will all be
compromised sooner or later after they have been developed and invented.
Here’s the point: Use wireless technologies for data communications in high security
applications only when you have absolutely no choice.
The fabric (radio waves) of wireless communication makes it difficult to secure
perfectly. Further compounding matters is the fact that as newer and stronger
encryption methods emerge, the processing powers of commodity computers also
keeps increasing, which helps in detecting and exploiting the weaknesses in the
methods.
If a wireless network is absolutely necessary in a high-security environment,
you need to put some best practices in place. These types of environments might
need multilayer protective mechanisms and a distributed infrastructure. This can
be expensive, because it means getting a dedicated server for all the individual
components that could have otherwise been consolidated. But a distributed security
infrastructure means that a compromise or weakness in one of the components does
not automatically mean a compromise of the remaining components.

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Home Environments
Home users should adhere to all commonsense wireless security principles and
properly protect their home wireless networks.
The following scenario shows what can happen if you don’t properly secure your
network:
1. A home user, Mr. A, subscribes to an Internet service provider (ISP) to access
the Internet. No problem.
2. The ISP has some of Mr. A’s personal information, such as his credit card
information, address, phone number, and so on. No problem.
3. Mr. A is connected to the Internet and all is going well. No problem.
4. Mr. A decides that he needs a wireless network at home, so he buys all the
necessary hardware (WAP, wireless adapter, and so on). No problem.
5. Mr. A gets back home and quickly hooks up the new wireless hardware to his
ISP’s network without securing the network. Problem!
6. Next door lives Mr. B. His Internet service was discontinued years ago by
another ISP because he violated the ISP’s terms of use. His violations included
illegal downloads and attempting to buy merchandise online with stolen credit
cards. He did his time on probation and is now back to his usual tricks with
another ISP.
7. Using his laptop, Mr. B easily connects to Mr. A’s unsecured wireless network
to use Mr. A’s access to the Internet. Mr. B resumes his illegal and illicit
activities on the Internet.
8. Mr. A’s ISP is notified that a customer is doing untoward things on the Internet.
The ISP investigates and finds out that the offending activity is originating
from the equipment registered to Mr. A.
9. The ISP alerts the police, gives them Mr. A’s address and phone number, and
then discontinues providing service to Mr. A. Mr. B gets off free and clear.
10. The police visit Mr. A, and the evidence against him is very strong. Mr. A may
be held liable and accountable for any crimes or illegal activities that malicious
third-parties (aka Mr. B) conducted against external networks while using
Mr. A’s home wireless network.
11. Mr. A gets himself a good lawyer. Fortunately, the lawyer has read this book,
so he understands how things like this can happen. The lawyer is able to prove
Mr. A’s innocence, but Mr. B is still a free man.
12. Mr. A has learned his lesson and secures his home wireless network.

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Summary
The Quad-W rule for deploying wireless networks is simple. You learned how it’s
used to survey, plan, and design a wireless network. You learned how to conduct a
site survey on a budget by walking through an actual site survey procedure using
commodity hardware. You also learned about the importance of interference and
security in several types of wireless network deployments.

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Appendix
Troubleshooting
Wireless Networks
283

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Key Skills and Concepts
■■ Learn basic and general troubleshooting techniques.
■■ Learn how to troubleshoot specific wireless networking issues.
Throughout this book, you’ve learned how to assemble and build all the pieces
of a wireless network in a controlled fashion. You learned about preselecting the
infrastructure hardware, choosing the client-side hardware, selecting the security
mechanisms, selecting the operating systems (OSs) that would be used on the client
systems, and so on. After such careful planning and staging, any wireless network
should just work seamlessly.
In reality, this is not always (or often) the case. You might not always have the
luxury of designing and building wireless networks from scratch. And even if you
do, things may not always work out as perfectly as they did for us in our examples.
A common scenario is that the wireless network administrator will inherit or manage
existing wireless networks. Another scenario is that you might be responsible for
building and connecting a wireless with an existing wired network. And, of course,
existing networks come with their own set of issues or constraints within which you
will have to operate.
This appendix is dedicated to scenarios for which things just don’t work out like
they should. The troubleshooting methodology will work like this:
■■ We will go all the way back to the beginning of this book and work our way
through each chapter and topic.
■■ Under each chapter and topic, some of the things that can go wrong will be
discussed, as well as the possible fixes.
■■ Some topics (and chapters) will have more troubleshooting information than
others, while some topics may not have any relevant troubleshooting aspects.
Tip  Even though this appendix has been organized into different sections based on some of the
preceding chapters, issues can arise from a single or a combination of any of these areas. So, in
general, you should always aim for the lowest hanging fruit when troubleshooting. This means that
you should address the issues that are easiest to solve or the issues that have the least impact on
the network before bringing out the big guns. The ability to easily recognize or identify the low-
hanging fruits comes with experience.
Let’s begin with troubleshooting regulatory and technical organization issues.

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Troubleshooting Regulatory and
Technical Organization Issues
The reasons for misbehaving or improperly functioning wireless networks that can be
attributed to regulatory issues can be simultaneously salient and trivial to troubleshoot.
As long as you remember that various countries and regions have different radio
spectrum usage and allocation rules, you’ll be ahead of the game.
So if, for example, you purchase infrastructure-side wireless hardware that was
originally designed to be used in Asia, Australia, and the Pacific Rim (Region 3), you
should not expect it to work properly with client-side hardware that was designed to
be used in North and South America and the Pacific (Region 2). Besides the obvious
interoperability issues, you may also be breaking local radio spectrum usage laws by
operating wireless equipment that does not conform to local rules and regulations.
In a similar vein, hardware used for wireless wide area network (WWAN)
communications or mobile broadband communications are also similarly affected. So,
for example, don’t expect to be able to set up a mobile broadband adapter that uses
Global System for Mobile (GSM) in a country or region where Code Division Multiple
Access (CDMA) is the prevailing cellular technology. If, however, your hardware
supports multiple modes or bands of operation, you stand a better chance of being able
use the hardware in different regions of the world.
Troubleshooting Client-Side Hardware Issues
On the client side, problems that can be attributed to hardware are pretty straightforward
to diagnose. Having said this, it should be noted that software issues can sometimes
manifest themselves in hardware, thereby making the hardware appear faulty. But once
you have ascertained that everything is fine on the software side, you can proceed to
diagnose client hardware issues. The subsequent sections cover software troubleshooting
methods.
Classic technology troubleshooting techniques start with a systematic elimination
and substitution process—you swap out suspect or dodgy hardware with other
hardware that is known to be good. Because typical client-side hardware has become so
commonplace and affordable these days, it may be prudent and expedient to begin your
troubleshooting efforts in this way. Again it’s all about the lowest hanging fruit—if it’s
quicker and easier to change the hardware, and your intuition tells you the hardware is
the problem, you can start from there.
Another cost-effective and quick approach to debugging and fixing hardware-
related problems is to look out for hardware switches and/or buttons that may need to
toggled to enable or power-on the wireless component in the device.

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Troubleshooting Infrastructure-Side Hardware Issues
Unlike the client-side wireless hardware, infrastructure-side equipment is often more
expensive and as such may not be so easy to swap out. In addition, infrastructure devices
these days are often multifunctional, in the sense that the device may serve multiple roles
or functions on the network. It may, for example, be used by both wireless clients and
wired clients. So if the device needs to be taken off-line for whatever reason, other critical
network services that are not wireless related may also be impacted.
Use the following information to help narrow down and troubleshoot problems
that are caused by infrastructure side hardware:
Symptom  Absolutely nothing is working, but everything seems fine at the client end.
Possible Fix  Reboot or power cycle the infrastructure device.
Impact  All network services that depend on the device might be affected.
Mitigation  The network should be designed using a layered approach. This means, for
example, that outages that affect wireless devices should not affect wired devices, if
separate layers of hardware are used for the wireless and wired devices. This will help
prevent having a single point of failure.
When financially feasible, equipment spares should always be handy. The spares
should, of course, be configured ahead of time. Having spares handy will help when
infrastructure hardware must be sent off for repairs.
Symptom  Only certain aspects of the network service provided by the infrastructure
hardware are functioning.
Possible Fixes  If available, review the system or error logs that the device generates to
understand the problem.
When possible, restart the specific service or functionality provided by the equipment.
Reboot or power cycle the equipment when all else fails. If the problem persists,
contact the hardware manufacturer for support.
Impact  Certain network services or functionality may be temporarily impacted.
Mitigation  A decent familiarity with your infrastructure devices is useful and will help
you know where to look for certain things, such as systems logs; it will also help to
know what commands to run or which buttons to click to control different functions.
Because nobody is expected to memorize the commands and syntax for the
gazillions of network equipment available today, you should at least know where to
look for information when its needed or know whom to ask.
Troubleshooting Issues with the Wireless Building Blocks
As mentioned in Chapter 2, wireless communication technologies rely on some
fundamental principles and concepts—the building blocks of all wireless technologies.
These principles govern the behavior of radio waves and the propagation of the radio

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Appendix:  Troubleshooting Wireless Networks 287
waves as they travel through space, and the building blocks are what make actual
wireless communications possible.
Numerous avoidable and unavoidable environmental and physical factors can
affect the proper functioning of wireless networks.
In general, having a decent understanding of wireless building blocks can help
you in troubleshooting. Use the following information to help narrow down and
troubleshoot problems that are caused by building blocks:
Symptom  There is no signal.
Possible Causes
a. The signal source may be switched off.
b. The receiver on the client STA may be switched off or disabled.
c. The wireless client STA may be too far away from the signal source or the
access point (AP).
d. Too many physical obstacles or barriers lie between the transmitter and the
receiver.
Fixes
a. Verify that the signal source is enabled.
b. Verify that wireless hardware on the receiver is enabled and working.
c. Relocate the STA to a location physically closer to the signal source.
d. Remove the obstacles or barriers if possible.
Symptom  Signal strength is low.
Possible Causes
a. The wireless client STA is too far away from the signal source or the AP.
b. Too many obstacles lie between the transmitter and the receiver.
Fixes
a. Relocate the STA to a location physically closer to the signal source. If possible,
use a better antenna on the client STA. If possible, use a better antenna on the
infrastructure device to focus or channel the wireless signal.
b. Remove the obstacles or barriers if possible.
Symptom  Strong signal, but no connection.
Possible Cause  Other aspects of the wireless network are the cause.
Fixes  See the troubleshooting infrastructure and TCP/IP troubleshooting issues
techniques.

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Symptom  Low data rates.
Possible Causes
a. RF channels are overcrowded.
b. RF modulation methods are not being used in an optimal way.
c. The network is poorly designed.
Fixes
a. Change the channels being used for wireless communications to less crowded
RF channels.
b. Make sure that the transmitting devices as well as the receiving devices
are using the most optimal modulation techniques. For example, the use of
802.11b-based clients in 802.11g wireless networks can impact the overall data
rates at which the normally faster 802.11g can communicate.
Remember that the building blocks for wireless communications force a trade-
off between data rates and distance. So if you want high data rates, you may
have to settle for modulation techniques that provide high data rates at short
distances.
c. Make sure that the wireless network is used for applications for which it is
capable of handling. For example, don’t expect to be able to stream high-
definition (HD) video content over an IEEE 802.11b network infrastructure.
Symptom  Packet loss.
Possible Cause  RF noise or interference.
Fix  Find and eliminate the sources of the interference.
Symptom  Intermittent connectivity issues.
Possible Causes
a. RF interference.
b. Oversubscribed wireless network.
Fixes
a. Find and eliminate the sources of interference. Check to determine whether the
intermittent connection happens at certain times during the day. If it does, find
out what event coincides with the disturbance and deal with that. For example,
you may find that the event occurs mostly during lunch periods when the
microwave oven is in constant use.
b. This issue may be a result of inadequate capacity planning. This means that
you may have too many wireless client devices trying to access the network at
the same time, thereby overloading the AP.

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Symptom  Frequent wireless client disconnections and reconnections.
Possible Causes  The driver for the wireless adapter is faulty, or other parts of the
system to which the wireless adapter connects might be faulty.
Fixes  Look to the device manufacturer for updated drivers for the client adapter. If
possible, switch out the wireless adapter for a known good one and see if the problem
persists. If the issue continues, something is wrong with other hardware parts of the
wireless station.
Problems with Establishing Wireless Connections
To troubleshoot issues that can occur when a wireless client STA tries to establish a
wireless connection, you need to understand the steps or stages involved during the
process: scanning, selection, authentication, association, and TCP/IP configuration.
Problems can arise during one or more of these stages, and your being able to identify the
exact stage at which the problem occurs can help to simplify the task of troubleshooting.
Scanning
Wireless clients scan to search and locate wireless networks to which they can connect.
Scanning occurs via the use of information embedded within special wireless management
frames, called beacons, sent periodically by infrastructure devices. Beacons are similar to
advertisements in wireless networking. The advertisement contains information such as
network name (SSID), wireless channel information, supported data rates, and time stamps.
Scanning can be either passive or active.
Passive Scanning
In passive scanning, the wireless STA is placed in a listening mode. It listens for
beacons being transmitted by APs. The STA does not need to do anything special when
operating in this mode.
Virtually all of today’s APs make it possible to suppress the advertisement of
network names through a configuration option that’s called something like “Prevent
SSID broadcast” or “Hide wireless network name.” Passive scanning by wireless clients
is a little more tricky but not impossible when the network name is hidden or cloaked
by the WAP. The wireless client STA needs to explicitly know the name of the wireless
network to join it when the network name is not being broadcasted.
When the option to hide the SSID on the WAP is enabled, it is always a good idea
to “unhide” the network name temporarily when you’re troubleshooting wireless
connectivity issues that may occur at the scanning stage.
Active Scanning
In active scanning, the wireless client STA is placed in a probing mode. This means
that the STA actively probes or queries the wireless airwaves for information about
available wireless networks. The STA sends out a special type of wireless management

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frame known as a probe request. Available infrastructure devices, such as WAPs, respond
to probe request frames with “probe response” frames.
Active scanning can be initiated by a wireless STA under several scenarios. In one
scenario, the STA is in a new environment and has no prior knowledge of any available
wireless networks. The STA begins an active scan of the so-called “any” wireless
network name or SSID. The “any” here simply means that the SSID is not specified or
has a null value. All WAPs and other such infrastructure devices that are configured to
broadcast their availability respond to the client. The client can then select the desired
wireless network name to which it will connect.
In another scenario, the STA is within the range of a wireless network or
environment in which it was previously configured to participate. The STA begins
an active scan for the previously configured network. This is how portable wireless
devices appear to remember and connect to wireless networks to which they’ve
connected in the past as long as they are within physical range of the network.
Selection
The selection stage occurs whenever a wireless client STA tries to connect to a wireless
network. Note that selection happens at the client end—specifically, it occurs within
the connection management software or utility on the STA. And, more important, the
act of selecting an AP or wireless network does not guarantee anything. You can select
any network, but other factors come into play to ensure a successful final connection.
Selection is just one of the steps.
It was mentioned earlier that the management beacon frames contain information
that advertises information about the wireless network, such as network name (SSID),
wireless capabilities, supported data rates, and signal strength. Some of this information
comes in handy during the selection stage. Let’s look at how these factors are used in the
selection stage.
Wireless Network Name
The wireless network name (SSID) is, among other things, information used by
the wireless client STA to identify the wireless networks to which it has previously
connected. It is also used to identify the wireless networks to which the STA has been
preconfigured to connect.
When duplicate wireless network names appear, other factors are considered when
choosing an SSID—for example, the SSID from the AP with the strongest signal will be
selected for pairing with the wireless STA.
Wireless Capabilities
Wireless capabilities are important factors to consider when a wireless client STA is
trying to select an AP or a distribution system with which to connect. The capabilities
advertised by APs can include the data rates supported by the AP, the supported
security options, the supported radio channels and/or frequencies, and the supported
IEEE 802.11 MAC and PHY types.

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The STA compares its own capabilities with those advertised and supported by the
AP and makes a selection based on what provides the best fit. As a simple example, a
wireless client STA that supports and implements the IEEE 802.11g standard will tend
to favor an AP that advertises and supports IEEE 802.11g as opposed to another AP that
supports only the IEEE 802.11b standard.
Signal Strength
The wireless STA can use the signal strength information of the AP stored in the
probe response frame to select an AP with which to connect. The higher the value of
the signal strength, the better the affinity of the STA to want to connect to that AP.
The signal strength value can also be used as a sort of tie-breaker when all the other
selection factors are equal.
Authentication
At the authentication stage in the wireless connection setup, the wireless client STA needs
to prove that it is indeed permitted to use or connect to the wireless or network resources.
Sometimes the infrastructure-side wireless devices also need to prove or confirm their
own identities, too. This is known as mutual authentication and is determined by type
of security mechanisms in place. You read about different authentication techniques in
Chapter 11.
At this stage, the security mechanisms that have been preconfigured on the wireless
infrastructure devices come into play. The encryption and decryption ciphers and
cryptographic systems are used.
Needless to say, a lot can go wrong here and can lead to hours and hours of
troubleshooting. For example, a single mistyped character can throw things off.
Following are some problems and possible fixes for several scenarios.
Problem  Characters were mistyped.
Things to Check and Possible Fixes  If possible, remove the security passphrase from the
infrastructure device and client device and start off with no security. If possible, change
the encryption keys to something simple that will be difficult to mistype. After you’ve
established that a mistyped character is the problem, you can go back and change to
more complicated or stronger passphrases.
Problem  Mismatched security settings: The infrastructure devices and client devices
must be using the same or a compatible security setting. For example, if the AP is
configured to authenticate clients using WPA2, and a wireless STA is trying to use
WPA, the authentication stage will not succeed.
Things to Check and Possible Fixes  Make sure that the security types and options configured
on the client STA match those that are configured on the infrastructure-side devices.
To eliminate a mismatched security setting being the cause of the authentication
problem, completely eliminate the use of encryption on both the infrastructure-side

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device and the client-side device. If things work using no encryption, you can work
your way up starting from low-strength encryption all the way to high-strength
encryption settings. This should be done until you find a mutually compatible setting
to use.
Problem  Interference: Under normal circumstances, interference is a nuisance in
wireless communication systems, because it simply disrupts the communication.
Interference can occur at any stage during the connection setup process or even after
the connection has been established. The probability of RF interference occurring at the
same instance as the authentication stage is slim but not impossible. When the effect of
RF interference is too great, it may prevent the authentication process from completing
successfully.
Things to Check and Possible Fixes  Try to eliminate or reduce all sources of RF
interference in the environment where wireless communication systems are in use.
Possible sources of interference are too numerous to list them all here. But some
examples include other wireless devices, other non-wireless electrical devices,
and unintentional emitters (microwave ovens, consumer electronics, light fixtures,
electric motors, power transmission lines, and so on).
Association
The association stage occurs after the authentication stage has been successfully
completed. Once the STA associates successfully, it becomes a part of the wireless basic
service set (BSS). During association, the minor little details of the wireless relationship
are ironed out.
Association begins by the wireless client STA sending an association request to the
infrastructure device. The association request frame contains information such as the
data rates supported by the client STA, the name of the wireless network (SSID), and
other special wireless extensions. The infrastructure device responds to the association
request with an association response.
Things rarely go wrong at this stage, but the association stage can fail even after a
successful authentication stage. When and if something does go wrong at this stage, the
problem may be out of the user’s control, because it may be caused by something as
low-level as the software driver. The wireless device driver on the client STA may, for
example, be advertising or requesting a functionality that the infrastructure device does
not support or understand. RF interference and poor signal strength can also hinder
association.
TCP/IP Configuration
Wired and wireless networks today are based on the venerable TCP/IP suite. This may
well change tomorrow when something better comes along, but this is the way things
stand today. This means that any wireless node that wants to communicate with other
nodes needs to be able to speak TCP/IP.

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In the TCP/IP configuration stage of a wireless connection setup, wireless client
STAs are provided their unique TCP/IP addressing configuration information. This
is needed by the STA for communicating with other STAs or with other network
resources, and it is also used by other network resources for communicating back with
the STA.
Various aspects of TCP/IP configuration as it pertains to wireless networking will
be discussed in the coming sections of this appendix.
Problems with Infrastructure Services and Protocols:
TCP/IP, DNS, and DHCP Issues
Infrastructure services work quietly and invisibly in the background of any wireless
network. These services are essential to the proper functioning of any wireless network
and actually make the wireless network useful to the end users.
The infrastructure services and protocols discussed here are implemented in
software. Thankfully, most of the services are based on well-defined and mature
standards, so troubleshooting procedures of services can be based on standard methods
and tools. However, the value and expediency that simple experience provides when
troubleshooting infrastructure protocol and service outages cannot be overemphasized.
Unfortunately, experience is not something that you learn in the classroom or from
a book. Experience is that thing—that je ne sais quoi. Experience is what tells the
network administrator to check that the network cable is properly plugged into the
equipment when the link or status light is off, before firing off the other complicated
debugging tools. Thankfully, you begin to build your experience repertoire once you’ve
fixed a problem more than once.
Following are some generic symptoms and solutions that can help you in
troubleshooting infrastructure services and protocol issues. Troubleshooting
techniques on specific OS platforms will be covered a bit later in the appendix.
Symptom  Network layer connectivity problems are occurring.
Things to Check and Possible Fixes  If available, check the system error logs.
Recent software changes or bugs may have affected the underlying network stack
(TCP/IP stack) of the system. Reset the network stack to a known working state if
possible.
These issues may also be caused by problems at the other layers. So, for example,
a problem that appears at the network layer may be resolved by checking the physical
cabling between any of the network components that depend on such cabling.
Symptom  Name-resolution problems are occurring.
Things to Check and Possible Fixes  Check the DNS server and its logs to look for
anomalies recorded there.

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Check to determine whether the issue affects a single system or the entire WLAN
system. If the issue affects only a single system, the problem might be a misconfiguration
at the client end.
Test to determine whether the name-resolution issues affect only the LAN systems
or the external or Internet residing hosts as well.
If wireless network clients are able to resolve the names of local systems properly
using the DNS server, the problem might be with the upstream DNS server to which
the internal DNS server forwards requests.
Symptom  Wireless network clients are unable to obtain network configuration
information (DHCP).
Things to Check and Possible Fixes  Check the DHCP server, and check the logs of the
DHCP server. Make sure that the DHCP server service is actually running. On certain
platforms, it may be necessary to explicitly authorize the DHCP server for the network
it will serve. Check the scope or range of the addresses that the DHCP server is leasing
out to clients.
If there are more wireless clients or wireless devices in use than the range the DHCP
server is authorized to manage, only some devices will be lucky enough to obtain a
DHCP lease from the server. In this case, you will need to increase the DHCP range to
accommodate the additional network clients.
Check to determine whether the issue is related to a specific client device or
whether it is a general problem that affects all the networked devices. If it affects only a
single device, check for the presence of a firewall at the server or client end that might
be causing the issue.
Symptom  Wireless network clients or devices are receiving incorrect network
configuration information (DHCP).
Things to Check and Possible Fixes  There might be a rogue AP or a rogue DHCP server
on the network that is giving out incorrect information to the wireless clients. You need
to track down the device and disable it.
Troubleshooting Networking Issues on Different OSs
Wireless capabilities can be found in all types of devices, in different shapes and sizes,
platforms, and applications. Regardless of how the wireless capabilities are implemented,
the underlying principles and technologies are all similar.
Earlier in the book, we used three popular computer OS platforms for demonstrating
wireless client configuration techniques: Windows, Apple OS X, and Linux-based Free
Open Source Software (FOSS). Let’s continue here by discussing how to troubleshoot and
fix different wireless issues on these platforms.

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Note  Some of the techniques and tools used here are OS-independent, but whenever this is not
possible or applicable, the specific differences are highlighted.
Table A-1 shows the locations for informational system messages and system
error messages, also called system logs, on these three platforms. These log resources
provide useful information that can aid in troubleshooting various wireless networking
issues on different platforms.
Table A-2 shows troubleshooting tools, problems, and symptoms that can occur
at OSI reference model layers 3 through 7. Note that most of these troubleshooting
tools and utilities are command-line–based, so you will type the command in the
appropriate command interpreter on the platform. In FOSS/Linux-based systems, the
command interpreter is also called the shell. Sample shell environments are bash, korn,
csh, and sh. You can get to the shell by using graphical front-ends gnome-terminal,
xterm, or konsole. The GUI front-end, known as xterm, also exists on Apple OS X. On
Windows systems, you can run the commands by using the cmd command interpreter.
Platform
FOSS/Linux
Apple OS X
MS Windows
Common Name
Location of System Log Files
System logs:
/var/log/messages
dmesg  Used for viewing the ring To view the current contents
buffer of the Linux kernel; shows
of the kernel’s ring buffer,
diagnostic messages as various events type dmesg. To monitor the
happen within the kernel, such as
dmesg output in real time,
detection of new hardware, loading type watch -n 1 "dmesg
and unloading of kernel modules
| tail".
(drivers), activation or deactivation
of network interfaces, diagnostic
information from modules for
wireless interfaces.
To view wireless connection
authentication, association,
deauthentication, and
disassociation messages as
iw  Displays information about
they are happening in real
wireless devices and for manipulating time, type iw event -f.
wireless device configuration.
Console  A repository for all the
various log files created by OS X.
Applications | Utilities |
Console
Event viewer  Displays various
Start | Control Panel |
information about significant
System and Maintenance |
events on the computer. Useful for Administrative Tools | Event
troubleshooting problems and errors. Viewer
Records system errors and other events.
Table A-1.  Locations of Informational System Messages and System Error Messages

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Symptoms, Problems, &
Objectives
TCP/IP: Verifying
and viewing TCP/IP
configuration information
Verifying and viewing
wireless configuration
specific information
Platform
Tool, Fixes & Things to Check
MS Windows ipconfig  Used for displaying, manipulating various TCP/IP
configuration parameters—e.g., to view current TCP/IP settings
of the local STA running MS Windows operating system type:
ipconfig /all
The command will display IP address, subnet mask, DNS server
address, the gateway address, hostname of the wireless STA
running an MS Windows operating system.
Apple OS X
ifconfig  Used for displaying and manipulating TCP/IP
configuration information for network interfaces on Macintosh
systems
FOSS/Linux ifconfig  Similar to the ipconfig command in Windows.
ip  Used for showing and manipulating TCP/IP configuration,
routing functions on FOSS-based systems.
FOSS/Linux iw  To view the device capabilities for all wireless devices, such
as RF band information, type:
iw list
To view wireless regulatory domain information for the wireless
device, type:
iw event -f
To display the wireless station statistic information, such as the
amount of tx/rx bytes, the last TX bit rate, type:
iw dev <interface_name> station dump

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Driver-related problems
MS Windows
MS Windows
FOSS/Linux
netsh  Use wlan context of the netsh utility. Some example
usages are listed next.
To display the entire collection of wireless device and wireless
networks information, type:
net wlan show all
To display a list of the current wireless interfaces on the system,
type:
net wlan show interfaces
To display the properties of the wireless adapter drivers on the
system, type:
net wlan show drivers
To display a list of wireless networks that are visible on the
system, type:
net wlan show networks
To display the current global settings of the wireless LAN, type:
net wlan show settings
Use Windows Device Manager to uninstall the device and its
driver. Reboot and then reinstall the driver.
modprobe  Adds and removes modules (drivers) from the Linux
Kernel—e.g., to remove a module named ath5k forcefully for a
wireless device, type:
modprobe -r ath5k
To load the module back again, type:
modprobe ath5k
Table A-2.  Troubleshooting OSI Upper Layer Problems on Different OS Platforms (Continued)

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Symptoms, Problems, &
Objectives
General TCP/IP problems
Platform
Universal
Tool, Fixes & Things to Check
ping  Generates and sends ICMP messages that can be used
to test TCP/IP settings of a system and test that other hosts are
reachable. Can be used to check that the TCP/IP stack installed on
the local system is functioning properly at a basic level.
If you suspect problems with the local TCP/IP stack of the STA,
you can begin troubleshooting by running a simple ping test to
probe the loopback interface on the STA. To test, type:
ping 127.0.0.1
If the above simple test fails, this is an indication that something
is very wrong with the TCP/IP stack on the local system. You can
begin fixing this by using the techniques in the repair sections of
this table.
Still, on checking the TCP/IP stack of the local STA, you should
try pinging the IP address of the STA. This too should succeed.
Type:
ping <IP-address-of-local-system>.
If everything checks out within the local system, you might want
to check that other systems are reachable on the local network.
Type:
ping <IP-address-of-remote-host>
The above test may fail, in certain situations. For example, if there
are intervening firewalls in use on the network, the firewalls may
prevent or block ICMP packets which the ping utility uses by
default. Host-based firewall software running on the local system
may also block ICMP packets.

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Address Resolution
Protocol (ARP)
TCP/IP: Repairing
If you suspect that the
software TCP/IP stack of
the local STA is corrupted
or otherwise confused, you
can try to repair it.
Universal
arp  After verifying that basic things are fine with the TCP/IP
stack of the local STA, but the STA can still not ping other local
systems, you could trying clearing out the local ARP cache for the
STA. If you can ping both the loopback address (127.0.0.1) and
your IP address, but you cannot ping any other IP addresses, use
the arp tool to clear out the ARP cache.
To view the current cache entries, type:
arp -n
To delete the entries, type:
arp -
MS Windows netsh  Use the netsh configuration utility (see Chapter 13) to
reset TCP/IP in Windows. This has the same effect as uninstalling
and reinstalling the TCP/IP protocol. Type:
netsh int ip reset logfile.txt
FOSS/Linux
This may be as simple as stopping and restarting the different
scripts that control the wireless network interface. Different
Linux-based distributions have different ways for doing this.
On Debian or Ubuntu platforms, type:
/etc/init.d/network-manager restart
or
/etc/init.d/network restart
or
restart network-manager
On Fedora or RHEL or Centos systems, type:
restart network
or
service network restart
On OpenSUSE or SUSE systems, type:
rcnetwork restart or service network restart
Table A-2.  Troubleshooting OSI Upper Layer Problems on Different OS Platforms (Continued)

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Symptoms, Problems, &
Objectives
General DHCP-related
issues
Platform
DHCP-related issues: The MS Windows
client may have incorrect
TCP/IP configuration or
is simply not getting any
TCP/IP configuration from
a working DHCP server. Try FOSS/Linux
manually forcing a DHCP
request.
Apple OS X
Tool, Fixes & Things to Check
You should first make sure that the wireless STA is indeed
configured to obtain its TCP/IP configuration information via
DHCP. It is possible that the STA is configured to use static
or manual IP configuration, and that statically configured
information may be incorrect.
Verify that the DHCP client software on the STA is running.
A listing of all running processes on the system, as well as the
system log files, are a good place to check for this.
The wireless STA must successfully complete all stages of
scanning, selection, authentication, and association before TCP/IP
configuration can complete successfully.
ipconfig  To force a request for new DHCP configuration, type:
ipconfig /renew
To release the current DHCP lease, type:
ipconfig /release
dhclient  Used for configuring network interfaces with the
DHCP.
To request a new DHCP configuration information or lease, type:
dhclient <name_of_interface>
To release the current DHCP lease, type:
dhclient –r
Disable and then re-enable wireless interface using the Connection
Manager applet.

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General routing problems:
These problems manifest
themselves as the inability
of the host system to reach
some networks and not
others. For example, a
STA may be able to reach
other systems on the same
network as itself but is
unable to reach systems on
other networks.
Universal
Unable to reach Internet
Universal
hosts. A wireless STA that is
able to communicate only
with other local systems but
is unable to communicate
with hosts on the Internet or
that reside on non-directly
connected networks; most
likely a routing-related
problem.
route  Displays and manipulates the routing table. Examining
the routing table on a wireless STA will help show how the STA
plans on reaching other networks.
To view the route table on an MS Windows system, you would
type:
route print
To view the route table on a Linux-based system, you would type:
route –n
Use the route utility to view the local routing table. If the STA
needs to reach other nondirectly connected networks, there
should be an entry for a default route in the routing tables. The
default route entry will have a reference to the “0.0.0.0” network.
Whenever this entry is absent, it means that the STA will not
know where to send packets destined for foreign networks, such
as the Internet.
The fix for this is to make sure that the STA has a default route
entry in its routing table.
In MS Windows systems, you would issue this command at a
command prompt (single line): route add 0.0.0.0 mask
0.0.0.0 <IP_ADDRESS_OF_GATEWAY>
In FOSS/Linux-based systems, you would issue this command at
a shell prompt (single line):
route add default gw \\ <IP_ADDRESS_OF_GATEWAY>
Table A-2.  Troubleshooting OSI Upper Layer Problems on Different OS Platforms (Continued)

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Symptoms, Problems, &
Objectives
General name resolution
issues: Common name
resolution methods are
NetBIOS, DNS, database,
local text files.
The litmus test for
identifying a name
resolution problem is when
a host system is unable
to communicate with
other systems using their
hostnames, but is able to
communicate with the
systems by other means,
such as via IP address.
Platform
MS Windows
FOSS/Linux
Tool, Fixes & Things to Check
nslookup  Simple utility for querying DNS servers interactively.
Please note that nslookup is also available on other operating
system platforms.
For example, to query the locally configured DNS server for the IP
address for the example.com domain, you would type:
nslookup example.com
nbtstat  This is used for displaying current NetBIOS information
that the local system knows about; also used for manipulating the
NetBIOS name cache.
dig  This is a powerful DNS lookup utility found in many Linux-
based distributions. Its syntax is simple.
For example, to query the locally configured DNS server for the IP
address for the example.com domain, you would type:
dig example.com
If you think that something is wrong with the locally configured
DNS server and you want to query using another DNS server:
dig @<DNS_SERVER_IP> example.com

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Name resolution issues:
Unable to reach external
hosts or sites using their
domain names.
A simple test to confirm
this scenario is by replacing
the friendly domain name
of any well known external
site with its IP address
and then substituting
this information for web
address for the site.
For example, if visiting
this web address
http://66.249.80.104 using
a web browser takes you to
Google’s home page while
http://www.google.com
fails, then you know you
have this problem.
Universal
If the wireless STA is able to browse Internet sites using only the
IP address of the remote host, it can mean either of the following:
The DNS server configured for the STA is unreachable or
unavailable.
The DNS server is reachable and available, but the DNS server
is itself unable to resolve external host names on behalf of the
wireless STA. This might be a problem with an upstream DNS
server that the local DNS server depends on.
Table A-2.  Troubleshooting OSI Upper Layer Problems on Different OS Platforms (Continued)

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304
Wireless Network Administration: A Beginner’s Guide
Summary
Some things that can go wrong in wireless networks were reviewed in this chapter.
Specifically, the different subject areas covered earlier in this book as well as the
common things that can go wrong in those areas were reviewed.
This appendix is by no means an exhaustive look at troubleshooting wireless
network systems, and it’s impossible to cover every single thing that can possibly go
wrong in a wireless network—a separate book would be required to do that, and that
book itself would span about 100 different volumes! I didn’t feel you’d want to read
such a boring book and so I didn’t write it!

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Index
References to figures are in italics.
2G cellular technologies, GSM, 90–94
3DES, 163
A
AAA, 144–146
access points (APs), 76
access server (AS), 144
accounting, 146
ACK frames, 84
active scanning, 289–290
ad-hoc networks
Linux, 262–265
Mac OS X, 229–230
aerials. See antennas
AirPort, 219, 222
AirPort Extreme, 219
AirPort Extreme Base Station, 219–220
airports, 278
airwaves, 5
See also waves
algorithms, 157–158
AM. See amplitude modulation (AM)
amplification, 19
amplitude, 19
amplitude modulation (AM), 27
amplitude-shift keying (ASK), 25
antennas
aesthetics, 62
beam width, 57
considerations for selecting, 61–62
directional, 61
equivalent isotropically radiated
power (EIRP), 55–56
gain and loss, 56–57
intentional radiator (IR), 55
mounting kits, 62
omnidirectional, 59–60
outdoor vs. indoor, 62
overview, 54–55
placement, 62
planar, 60
polarization, 57–58
safety, 62
semidirectional, 60
yagi, 60
305

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Wireless Network Administration: A Beginner’s Guide
anycast addresses, 120
Apple. See Mac OS X; Macintosh
ASK. See amplitude-shift keying (ASK)
association, 292
Association Request frames, 84
Association Response frames, 84
asymmetric encryption algorithms, 157
Australian Communications and Media
Authority (ACMA), 9
authentication, 144–145, 153, 154, 291–292
Authentication frames, 85
authoritative servers, 128–129
authorization, 145–146
B
b and g mode, 34
b only mode, 33
b43-fwcutter utility, 241
bands, 21–22
basic service areas (BSAs), 79
basic service set (BSS), 76–78
beacon frames, 84
beacons, 289
beam width, 57
bitwise AND operations, 118
block ciphers, 160–162
Bluetooth, 98
Dial-Up Network (DUN), 231–234
networks, 99–100, 101
profiles, 98, 100
protocols, 98, 99
SIGs and manufacturers, 101
standards, 98
versions, 100
bridges, wireless, 68–69
Broadcom drivers, 240
BSSID, 78
C
caching, 149
caching proxy servers, 149
caching servers, 130–131
Canadian Radio-Television and
Communications Commission (CRTC), 10
CAPWAP, configuring, 192
CBC-MAC, 167–168
CCMP/AES, 166
cell coverage, 271
CF cards, 50–51
cfg80211, 239
Challenge-Handshake Authentication
Protocol. See CHAP
channel bonding, 34
channels, 22
how channels map to frequencies in
the ISM band, 23
CHAP, 145
chipsets
components, 41–42
makers, 42–43
overview, 40–41
ciphers, 158–160
3DES, 163
concealment vs. running key, 160
DEA (DES), 162
implementations, 163–168
RC4, 163
stream vs. block, 160–162
substitution vs. transposition, 160
clear text. See plain-text
CLI, 243–249
generic Linux wireless client
configuration, 254–259
Communications Act of 1934, 8
Communications Act of 2003, 9
CompactFlash cards, 50–51
compatible addresses, 121
concealment ciphers, 160
confidentiality, 154
ConnMan, 243
constructive interference, 20
content-filtering proxy servers, 149
Control and Provisioning of Wireless
Access Points protocol. See CAPWAP
control frames, 84, 153
converters, 51
cost, hardware, 70
cryptographic manipulation, 153
cryptography. See public-private key
cryptography; security
CSMA/CD, 83
CTS frames, 84

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Index 307
D
data frames, 85, 154
data throughput, 270
DEA, 162
Deauthentication frames, 85
decryption, 155
demodulation, 41
demodulators, 22
DES, 162
destructive interference, 20
dhcp, 264
DHCP
clients, 137
options, 137
overview, 136
relay, 137–139
servers, 137
Dial-Up Network (DUN), 231–234
Diameter protocol, 147–148
directional antennas, 61
direct-sequence spread spectrum (DSSS), 24
Disassociation frames, 85
Distributed Coordination Function (DCF), 83
distribution system, 75
wireless distribution system (WDS), 76
DNS, 124
caching servers, 130–131
CNAME records, 134–135
domain and host naming
conventions, 124–128
forward resolution, 128
in-addr.arpa domain, 128
MX records, 134
NS records, 133
primary servers, 128–129
PTR records, 133–134
record types, 131–135
A records, 133
root domain, 125
root name servers, 130
RP records, 135
secondary servers, 129–130
second-level domain names, 126
SOA records, 131–132
subdomains, 126–128
third-level domain names, 126
top-level domain names, 125–126
TXT records, 135
zones, 128
dnsmasq, 264
Domain Name System. See DNS
DS. See distribution system
DSSS. See direct-sequence spread
spectrum (DSSS)
E
EAP, 145, 168–169
EAP-AKA, 172
EAP-PSK, 171
EAP-SIM, 172
EAP-TLS, 170–171
EAP-TTLS, 171
entities, 169
grammar, 169
efficiency, 30
encryption, 155
E-plane, 58
equivalent isotropically radiated power
(EIRP), 55–56
ETSI, 13
European Telecommunications Standards
Institute. See ETSI
exclusive OR (XOR), 156
ExpressCard, 48–49
extended service set (ESS), 79
Extensible Authentication Protocol. See EAP
F
FCC, 8–9
FDM, 25
Federal Communications Commission.
See FCC
FHSS. See frequency-hopping spread
spectrum (FHSS)
firmware, 241–242, 259–261
Fixed WiMAX, 97
FM. See frequency modulation (FM)
forward resolution, 128
four-way handshake, 173
FQDN. See fully qualified domain name
(FQDN)

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34.1 Page 331

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308
Wireless Network Administration: A Beginner’s Guide
frequency, 17–18
how channels map to frequencies in
the ISM band, 23
ISM frequencies, 21
UNII frequencies, 22
frequency modulation (FM), 27
frequency-division multiplexing. See FDM
frequency-hopping spread spectrum
(FHSS), 23–24
frequency-shift keying (FSK), 25
FSK. See frequency-shift keying (FSK)
fully qualified domain name (FQDN),
124–125
G
g only mode, 33
General Packet Radio Service. See GPRS
GMS, cells, 91
GPRS, 93–94
greenfields, 33
GSM
Base Station System (BSS), 92
GPRS, 93–94
GSM SIGs, 93
Mobile Station (MS), 92
Network Switching System (NSS), 92
overview, 90–91
H
HAL, 241–242
hardware
choosing, 51–52
CompactFlash cards, 50–51
converters, 51
cost, 70
estimating requirements, 270–271
ExpressCard, 48–49
interoperability, 70
Macintosh, 218–221
Mini PCI, 45
overview, 43–44
PC Card, 46–47
PCI, 44
PCI Express Mini, 45–46
planning and design considerations,
268–269
SDIO cards, 50–51
troubleshooting, 285–286
USB, 49–50
wireless hardware on Linux
platforms, 237
hash functions, 166–168
headers, 109
hertz, 17
hidden node problem, 83
high security areas, 279
High Speed Downlink Packet Access.
See HSDPA
High Speed Packet Access. See HSPA
High Speed Uplink Packet Access.
See HSUPA
HMAC, 167
home environments, 280–281
hospitals, 278
hosts, and networks, 116–117
HSDPA, 94
HSPA, 94
HSPA+ Evolved, 95
HSUPA, 95
Hz. See hertz
I
ICMP, 111
IEEE, 10–12
IEEE 802, 31
IEEE 802.11, 31–32, 33, 79–87
IEEE 802.11a, 33
IEEE 802.11b, 32
IEEE 802.11g, 33–34
IEEE 802.11i, 35–36, 172–174
IEEE 802.11k, 35
IEEE 802.11n, 34
IEEE 802.11y, 35
IEEE 802.15, 36
IEEE 802.3, 31
IEEE K band, 21
IETF, 12–13
ifconfig, 248

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Index 309
in-addr.arpa domain, 128
incompatibility, 269
independent BSS, 77
infrastructure BSS, 76
Institute of Electrical and Electronics
Engineers. See IEEE
integrity, 154
Intel Corporation, 97
Intel wireless drivers, 240–241
intentional radiator (IR), 55
International Telecommunication Union
Radiocommunication Sector. See ITU-R
Internet Connect Sharing (ICS), 210–214
Internet Engineering Task Force.
See IETF
Internet Protocol. See IP
Internet sharing, 226–229
interoperability, 30, 269
hardware, 70
ip, 249
IP
Different Services (DiffServ) field, 110
Flags field, 110
Fragmentation Offset field, 110
Header Checksum, 111
Identification Number field, 110
Length field, 110
overview, 108–109
Protocol field, 111
Source and Destination IP Address
fields, 111
Total Length field, 110
TTL field, 110–111
Version field, 110
IP-based networks, 116–119
iptables, 264
IPv4, 109
class ranges, 116
IPv6, 119
address format, 119–120
address types, 120
backward-compatibility, 121
ipwXXXX, 241
ISM band, 21
how channels map to frequencies in
the ISM band, 23
ITU-R, 5, 7–8
iw, 239, 244–245, 246
iwconfig, 244
iwl3945, 241
iwlagn, 241
iwlwifi Project, 240–241
K
key management, 165
keys, 155
keyspace, 155
keystream, 156
L
LANs, IEEE 802.3, 31
licenses, 5
lite license, 35
Linux, 236
ad-hoc networks, 262–265
CLI, 243–249
ConnMan, 243
generic wireless client configuration,
254–259
Mac80211, 238–239
NetworkManager, 242–243
wireless API, 237–239
wireless drivers, 237, 239–242
Wireless Extensions API, 238
wireless hardware on Linux
platforms, 237
Wireless Interface Connection
Daemon, 243
See also Ubuntu
lite license, 35
local area networks. See LANs
loopback addresses, 116
LTE, 95–96
M
MAC frames, 85
fields, 86–87
types, 84–85, 153–154
MAC layer, 82–85, 254–256

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Wireless Network Administration: A Beginner’s Guide
Mac OS X
ad-hoc networks, 229–230
Bluetooth Dial-Up Network, 231–234
changing connection preferences, 225
Internet sharing, 226–229
setting up a wireless location,
221–225
setting up hardware, 220–221
WAP specifications, 220
wireless Mac client specifications, 221
See also Macintosh
Mac80211, 238–239
MAC/BBP, 41
Macintosh
hardware, 218–219
software, 218
wireless hardware, 219–220
See also Mac OS X
MadWifi Driver Project, 239–240
management frames, 84–85, 153
MANs, IEEE 802, 31
mapped addresses, 121
Master Session Key (MSK), 173
Media Access Controller and Baseband
Processor. See MAC/BBP
Medium Wave (MW) band, 21
mesh networks, 214–215
message authentication code, 166
message integrity code, 166
metropolitan area networks. See MANs
Microsoft Challenge-Handshake
Authentication Protocol. See
MS-CHAP
Mini PCI, 45
Mini PCIe, 45–46
mobile units (MUs), 75
Mobile WiMAX, 97
modulation, 22–23, 41
analog modulation techniques,
26–27
digital modulation techniques, 24–26
spread-spectrum modulation
techniques, 23–24
modulators, 22
MS-CHAP, 145
multicast addresses, 120
mutual authentication, 291
See also authentication
N
NATO K band, 21
netmasks, 117–119
Netsh utility, 206–209
configuring SoftAP and VWiFi,
210–212
network access server (NAS), 143
network reliability, 270
NetworkManager, 242–243
networks, and hosts, 116–117
nix-WAP-2012, 181
configuring, 182–186
specifications, 182
nix-WLC-2012, configuring, 187–194
nl80211, 239
nm-tool, 247
Ubuntu wireless client configuration,
249–253
O
OFDM, 25
Office of Communications (Ofcom), 9
omnidirectional antennas, 59–60
orthogonal frequency-division
multiplexing. See OFDM
oscillation, 17
OSI model, 79, 80
MAC layer, 82–85
Physical (PHY) layer, 79–82
P
Pairwise Master Key (PMK), 173
PANs, 215
IEEE 802, 31
PAP, 145
passive scanning, 289
Password Authentication Protocol. See PAP
PC card standard, 46–47
PCI, 44
PCI-SIG, 44
personal area networks. See PANs
phase, 19–20

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phase difference, 20
phase-shift keying (PSK), 25–26
Physical (PHY) layer, 79–82, 254–256
plain-text, 154–155
planar antennas, 60
point-to-multipoint links, 69
point-to-point links, 68–69
polarization, 57–58
Power over Ethernet (PoE), 69
prevention of vendor lock-in, 30
primary servers, 128–129
primitives, 76
private IPs, 117
Probe Request frames, 85
probe requests, 290
Probe Response frames, 85
proprietary drivers, 259–261
protection mechanism, 34
proxy servers, 148–149
popular implementations, 150
types of, 149
when to use, 150
PSK. See phase-shift keying (PSK)
public-private key cryptography, 158, 159
Q
QAM, 26
Quadrature Amplitude Modulation.
See QAM
R
radio frequency, 18
radio frequency (RF) transceiver, 42
radio waves, 5, 17
See also waves
RADIUS, 142–144
popular implementations, 147
when to use, 146
RC4, 163
Reassociation Request frames, 84
Reassociation Response frames, 84
received amplitude, 19
received signal strength (RSS), 271
alternatives, 273
Index 311
receiver sensitivity, 52
regulatory organizations
Australian Communications and
Media Authority (ACMA), 9
Canadian Radio-Television and
Communications Commission
(CRTC), 10
FCC, 8–9
ITU-R, 5, 7–8
map of international regulatory
bodies, 6
national radio communications
regulatory bodies, 6
Office of Communications (Ofcom), 9
overview, 5
Telecom Regulatory Authority of
India (TRAI), 9–10
troubleshooting issues with, 285
regulatory regions, 7–8
Requests for Comment. See RFCs
retail environments, 278–279
RF. See radio frequency
RF interference, 272
RFCs, 12
root name servers, 130
root servers, 126
routers, wireless, 67–68
RTS frames, 84
running key ciphers, 160
tabula recta, 161
Rx sensitivity, 52
S
scanning, 289–290
SDIO cards, 50–51
secondary servers, 129–130
security
algorithms, 157–158
background, 152–154
decryption, 155
encryption, 155
keys, 155
keyspace, 155
keystream, 156
plain-text, 154–155
services, 154

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Wireless Network Administration: A Beginner’s Guide
selection, 290–291
semidirectional antennas, 60
servers
access server (AS), 144
authoritative servers, 128–129
caching servers, 130–131
DHCP, 137
network access server (NAS), 143
primary servers, 128–129
proxy servers, 148–150
root name servers, 130
root servers, 126
secondary servers, 129–130
signal strength, 291
signaling techniques, 80, 81–82
signal-to-noise ratio (SNR), 271
sine waves, 17, 18
See also waves
site deployment examples and
considerations
airports, 278
high security areas, 279
home environments, 280–281
hospitals, 278
retail environments, 278–279
site surveys, 271
example, 274–277
metrics, 271
RF interference, 272
tools, 272–273
software access point (SoftAP), 210
configuring using netsh, 210–212
SOHO/residential wireless routers.
See SRWRs
SRWRs, 67–68
SSID, 78, 290
standards, 10
Bluetooth, 98
ExpressCard, 48–49
IEEE 802, 31
IEEE 802.11, 31–32, 33, 79–87
IEEE 802.11a, 33
IEEE 802.11b, 32
IEEE 802.11g, 33–34
IEEE 802.11i, 35–36, 172–174
IEEE 802.11k, 35
IEEE 802.11n, 34
IEEE 802.11y, 35
IEEE 802.15, 36
IEEE 802.3, 31
IEEE standards formulating process,
11–12
Mini PCI, 45
overview, 30
PC Card, 46–47
PCI, 44
PCI Express Mini, 45–46
USB, 49–50
See also ETSI; IEEE; IETF;
Wi-Fi Alliance
STAs, 56, 74–75
modes, 75
and wireless controllers, 65–66
stream ciphers, 160
subdomains, 126–128
subnetting, 117
substitution ciphers, 160
symmetric encryption algorithms, 157
system messages, locations of
informational system messages and
system error messages, 295
T
tabula recta, 160, 161
TCP
connection overview, 113–115
header length, 112
Miscellaneous Flags field, 113
overview, 111–112
Sequence and Acknowledgment
fields, 112
Source and Destination Port
fields, 112
TCP Checksum field, 113
Urgent Pointer field, 113
Window Size field, 113
TCP/IP, 108
configuration, 292–293
IP, 108–111
TCP, 111–115
technical organizations
ETSI, 13

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Index 313
IEEE, 10–12
IETF, 12–13
overview, 10
troubleshooting issues with, 285
Wi-Fi Alliance, 13–14, 34, 36
Telecom Regulatory Authority of India
(TRAI), 9–10
Telecommunications Act, 8
temporal keys, 173
Time Capsule, 220
TKIP/WPA, 164–165
TLDs. See top-level domains
top-level domains, 125–126
transient keys, 173
Transmission Control Protocol. See TCP
transmit amplitude, 19
transmit power, 52
transmitter, 19
transparent proxy servers, 149
transposition ciphers, 160
troubleshooting
client-side hardware issues, 285
infrastructure services and protocols,
293–294
networking issues on different OSs,
294–303
OSI upper layer problems on
different OS platforms, 296–303
regulatory and technical organization
issues, 285
wireless building block issues,
286–289
wireless connections, 289–293
tunneling, 121
Tx power, 52
U
Ubuntu wireless client configuration,
249–253
UDP, 115
UMTS, 94–95
unicast addresses, 120
UNII band, 22
USB, 49–50
User Datagram Protocol. See UDP
V
Very High Frequency (VHF) band, 21
Virtual WiFi (VWiFi), 209–210
configuring using netsh, 210–212
W
WAP, 181
bridge mode, 63
configuring, 182–186
modes, 63–64
overview, 62–63
repeater mode, 64
root mode, 63
specifications, 198
specifications of the nix-WAP-2012, 182
when to use, 65
wavelength, 18–19
waves, 16–17
See also airwaves; radio waves
WCs, 65–67
web proxy servers, 149
WEP, 35–36, 163–164
wicd, 243
Wi-Fi Alliance, 13–14, 34, 36
Wi-Fi Protected Access. See WPA
WiMAX, 96–97
WiMAX Forum, 97
Windows 7 wireless features
Internet Connect Sharing (ICS),
210–214
mesh networks, 214–215
PANs, 215
software access point (SoftAP), 210–214
Virtual WiFi (VWiFi), 209–214
Windows clients
compatibility, optimization and
suitability considerations, 205
manually connecting to a wireless
network, 205–206
setting up a wireless profile, 201–204
setting up hardware, 199–201
WAP specifications, 198
wireless client specifications, 199
wireless network configuration
cloning with Netsh, 206–209

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Wireless Network Administration: A Beginner’s Guide
Wired Equivalent Privacy. See WEP
wireless access point. See WAP
wireless bridges, 68–69
wireless building blocks, troubleshooting
issues with, 286–289
wireless capabilities, 290–291
wireless controllers, 65–67
wireless distribution system (WDS), 76,
77–78
Wireless Extensions API, 238
Wireless Interface Connection Daemon, 243
wireless medium (WM), 74
wireless metropolitan area networks.
See WMANs
wireless network management utilities, 204
wireless network name. See SSID
wireless personal area networks.
See WPANs
wireless routers, 67–68
wireless stations. See STAs
wireless switches and controllers, 65–67
wireless wide area networks. See WWANs
WLAN controller, 186–187
configuring, 187–194
WLANs
access points (APs), 76
basic service areas (BSAs), 79
basic service set (BSS), 76–78
basic service set ID (BSSID), 78
defined, 74
distribution system, 75
extended service set (ESS), 79
IEEE 802.11 standard, 79–87
service set ID (SSID), 78
stations, 44
wireless medium, 74
wireless stations (STAs), 74–75
WMANs
overview, 96
WiMAX, 96–97
Worldwide Interoperability for Microwave
Access. See WiMAX
WPA, 36, 164–165
wpa_passphrase, 247
wpa_supplicant, 245–247
WPA2, 165–168
WPANs
Bluetooth, 98–101
IEEE 802.15, 36
overview, 97–98
ZigBee, 101–104
WWANs, 90
GSM, 90–94
LTE, 95–96
UMTS, 94–95
X
XOR, 156
Y
yagi antennas, 60
Z
ZigBee
components and architecture,
102, 103
overview, 101–102
SIGs and manufacturers, 104
special features, 102
versions, 102
zones, 128