Building a wireless office

282 Pages·2003·5.805 MB·English

by  Gilbert Held

BUILDING
A
WIRELESS
NETWORK
GILBERT HELD
AUERBACH PUBLICATIONS
A CRC Press Company
Boca Raton London New York Washington, D.C.
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Library of Congress Cataloging-in-Publication Data
Held, Gilbert, 1943-
Building a wireless office / Gilbert Held.
p. cm.
Includes index.
ISBN 0-8493-1271-X (alk. paper)
1. Wireless LANs. I. Title.
TK5105.78 .H4497 2002
004.6'8--dc21
2002071209
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Library of Congress Card Number 2002071209
ISBN 0-203-97271-6 Master e-book ISBN
Dedication
Being on the faculty of a school of higher education has both privileges and
responsibilities. In addition, it provides an author with a human laboratory of
inquisitive minds that enable different presentation concepts to be tested and
refined.
The ability to teach at Georgia College and State University is a truly enjoyable
experience. I have been fortunate to have students with a mixture of backgrounds
that have provided different views concerning the operation and utilization of both
wired and wireless LANs. Recognizing that learning is a two-way process, this
book is dedicated to the students at Georgia College and State University as well
as the person who provided me with the opportunity to teach there. Thus, to Dr.
Harry Glover I would like to both publicly say “thank you” and dedicate this book
to him.
v
Contents
Introduction...............................................................................................xvii
1 Introduction to Wireless LANs....................................................................1
Wireless Networking Devices........................................................................................1
Wireless LAN Network Adapters...............................................................................2
Access Point..............................................................................................................3
Types of Networking............................................................................................4
Wireless Bridge..........................................................................................................5
Wireless Routers........................................................................................................6
Wireless Access Server..............................................................................................7
Rationale for Wireless LANs...........................................................................................8
Economics.................................................................................................................8
Adds, Moves, and Changes.........................................................................................9
Roaming...................................................................................................................10
Disadvantages to Wireless LANs..............................................................................11
Learning New Technology..................................................................................11
Proliferation of Standards...................................................................................11
Security...............................................................................................................12
Applications.............................................................................................................13
Home Use...........................................................................................................13
Hospital...............................................................................................................15
College Campus..................................................................................................15
Office Support....................................................................................................16
Portals.................................................................................................................17
Book Preview...............................................................................................................18
Technology and Terminology..................................................................................18
IEEE Standards.........................................................................................................18
Basic Wireless LAN Operations...............................................................................18
The TCP/IP Protocol Suite.......................................................................................19
Security....................................................................................................................19
Working with Vendor Products...............................................................................19
The Future...............................................................................................................19
vii
viii Building a Wireless Office
2 Technology and Terminology...................................................................21
Basic Communications Concepts................................................................................21
Frequency................................................................................................................21
Wavelength..............................................................................................................23
Bandwidth...............................................................................................................25
Modulation Methods....................................................................................................26
Amplitude Modulation.............................................................................................26
Frequency Modulation.............................................................................................27
Phase Modulation....................................................................................................28
The Nyquist Relationship...................................................................................28
Quadrature Amplitude Modulation..........................................................................29
Differential Modulation...........................................................................................31
Signaling Methods........................................................................................................32
Infrared....................................................................................................................33
Types of Infrared Transmission...........................................................................33
Limitations..........................................................................................................33
Frequency Hopping Spread Spectrum....................................................................34
Rationale for Spread Spectrum...........................................................................34
Operation............................................................................................................34
Direct Sequence Spread Spectrum.........................................................................35
Operation............................................................................................................35
Orthogonal Frequency Division Multiplexing........................................................36
Evolution.............................................................................................................36
Operation............................................................................................................37
The Frequency Spectrum and Wireless LANs.........................................................37
ISM Bands...........................................................................................................37
Where Wireless LANs Reside..............................................................................38
Measurements..........................................................................................................39
Power Ratios.......................................................................................................39
Bel.......................................................................................................................39
Decibel................................................................................................................40
Decibel-Milliwatt.................................................................................................41
Signal-to-Noise Ratio...........................................................................................42
Channel Capacity................................................................................................43
Antenna Considerations......................................................................................45
Radiation Pattern................................................................................................45
Beamwidth..........................................................................................................45
Antenna Gain......................................................................................................46
Wireless LAN Terminology...........................................................................................47
Architecture..................................................................................................................47
The Station..............................................................................................................47
Network Topologies................................................................................................48
Ad Hoc Networking............................................................................................48
Infrastructure Networking..................................................................................48
Access Point Operation...........................................................................................49
The Distribution System..........................................................................................50
The Extended Service Set...................................................................................50
Media Access Control...................................................................................................50
CSMA/CA.................................................................................................................50
The Hidden Node Problem.....................................................................................51
ix
3 IEEE Standards.............................................................................................53
Basic Architecture.........................................................................................................53
Layer Separation...........................................................................................................53
Physical Layer Operation.............................................................................................54
Infrared....................................................................................................................54
Frequency Hopping Spread Spectrum....................................................................55
Modulation..........................................................................................................55
Frequency Channels...........................................................................................55
Direct Sequence Spread Spectrum.........................................................................56
Barker Code........................................................................................................56
Modulation..........................................................................................................56
Comparison to FHSS...........................................................................................56
Complementary Code Keying............................................................................57
Code Sets............................................................................................................57
Orthogonal Frequency Division Multiplexing....................................................58
Frequency Allocation..........................................................................................58
Scope of Coverage..............................................................................................58
Physical Layer Operations............................................................................................59
FHSS.........................................................................................................................59
DSSS.........................................................................................................................60
OFDM......................................................................................................................60
MAC Layer Operations.................................................................................................61
Layer 2: Framing......................................................................................................61
Protocol Version Field.........................................................................................62
Type and Subtype Fields....................................................................................62
ToDS/FromDS Fields...........................................................................................62
More Frag Field...................................................................................................62
Retry Field..........................................................................................................62
Power Management Field...................................................................................63
More Data Field..................................................................................................64
WEP Field............................................................................................................64
Order Field..........................................................................................................64
Duration/ID Field................................................................................................65
Address Fields.....................................................................................................65
Sequence Control Field......................................................................................66
Frame Body Field................................................................................................66
CRC Field............................................................................................................66
Management Frames................................................................................................67
The Beacon Frame..............................................................................................67
The Probe Response Frame................................................................................67
Control Frames........................................................................................................68
Hidden Nodes.....................................................................................................68
Use of RTS and CTS Frames...............................................................................69
RTS and CTS Frame Formats..............................................................................69
ACK Frame..........................................................................................................70
Media Access............................................................................................................70
Time Gaps...........................................................................................................70
DCF Operation....................................................................................................71
PCF Operation....................................................................................................72
x Building a Wireless Office
4 Basic Wireless LAN Operations.................................................................75
Ad Hoc Networking.....................................................................................................75
Adapter Card Setup......................................................................................................76
Configuring a Wireless Network Adapter................................................................77
Ad Hoc Settings..................................................................................................77
TxRate.................................................................................................................78
WEP.....................................................................................................................78
PS Mode..............................................................................................................78
Channel...............................................................................................................78
Network Software....................................................................................................80
Enabling File and Print Sharing..........................................................................80
Assigning Identifiers...........................................................................................81
Sharing Network Resources...............................................................................81
Setting TCP/IP Parameters..................................................................................85
The Proof Is in the Pudding....................................................................................89
Internet Connection Sharing...................................................................................90
Installation..........................................................................................................91
Configuration......................................................................................................92
Infrastructure Operations.............................................................................................94
Wireless Router Configuration.....................................................................................94
Access the Router...................................................................................................95
Configuring a PC IP Address..............................................................................95
Configuring the DNS..........................................................................................95
Gateway Configuration.......................................................................................95
Using Your Browser.................................................................................................97
Accessing the Configuration Setup Utility.........................................................97
Using the Setup Wizard......................................................................................99
System Name Assignment...................................................................................99
Wireless LAN Setup Parameters.........................................................................99
Defining the Wired Connection.......................................................................103
Defining Address Assignments..........................................................................103
Internet Access via the Router..............................................................................106
Site Selection.........................................................................................................106
5 TCP/IP Protocol Suite...............................................................................109
The Internet Protocol................................................................................................109
Datagrams and Segments.......................................................................................110
Datagrams and Datagram Transmission.................................................................110
Routing..................................................................................................................110
The IP Header.......................................................................................................111
Vers Field..........................................................................................................111
Hlen Field..........................................................................................................111
Service Type Field.............................................................................................112
Total Length Field.............................................................................................113
Identification and Fragment Offset Fields........................................................113
Flags Field.........................................................................................................115
Time to Live Field.............................................................................................115
Protocol Field....................................................................................................115
Header Checksum Field....................................................................................116
Source and Destination Address Fields.............................................................116
IP Addressing..............................................................................................................116
The IP Addressing Scheme....................................................................................120
xi
Address Classes......................................................................................................121
Rationale...........................................................................................................122
Class Addressing Overview...............................................................................122
Class A Addresses..............................................................................................123
Class B Addresses..............................................................................................125
Class C Addresses..............................................................................................125
Class D Addresses.............................................................................................126
Class E Addresses..............................................................................................127
Dotted Decimal Notation......................................................................................127
Basic Workstation Configuration...........................................................................128
Reserved Addresses...............................................................................................131
Subnetting..............................................................................................................133
Overview..........................................................................................................133
Subnetting Example..........................................................................................133
Host Restrictions...............................................................................................135
The Zero Subnet...............................................................................................136
Internal Versus External Subnet Viewing.........................................................136
Using the Subnet Mask.....................................................................................137
Multiple Interface Addresses.................................................................................139
Address Resolution................................................................................................140
Ethernet and Token Ring Frame Formats.........................................................141
LAN Delivery....................................................................................................141
Address Resolution Operation..........................................................................142
ARP Packet Fields.............................................................................................142
Locating the Required Address.........................................................................143
Gratuitous ARP..................................................................................................143
Proxy ARP.........................................................................................................143
RARP.................................................................................................................144
ICMP...........................................................................................................................144
Overview...............................................................................................................144
The ICMP Type Field........................................................................................145
The ICMP Code Field.......................................................................................145
Evolution................................................................................................................145
The Transport Layer...................................................................................................146
TCP Overview............................................................................................................148
The TCP Header....................................................................................................148
Source and Destination Port Fields..................................................................148
Multiplexing and Demultiplexing.....................................................................149
Port Numbers...................................................................................................149
Well-Known Ports.............................................................................................150
Registered Ports................................................................................................150
Dynamic or Private Ports.................................................................................150
Sequence and Acknowledgment Number Fields.............................................151
Hlen Field..........................................................................................................152
Code Bits Field..................................................................................................153
Window Field....................................................................................................153
Checksum Field................................................................................................154
Urgent Pointer Field.........................................................................................154
Options Field....................................................................................................154
Padding Field....................................................................................................154
Connection Establishment.........................................................................................155
Connection Function Calls....................................................................................155
xii Building a Wireless Office
Port Hiding............................................................................................................155
Passive OPEN.........................................................................................................156
Active OPEN..........................................................................................................156
The Three-Way Handshake....................................................................................156
Overview..........................................................................................................157
Operation..........................................................................................................157
The TCP Window...................................................................................................158
Avoiding Congestion.............................................................................................159
TCP Slow Start..................................................................................................160
The Slow-Start Threshold..................................................................................160
TCP Retransmissions.............................................................................................161
Session Termination...............................................................................................161
UDP............................................................................................................................162
The UDP Header...................................................................................................162
Source Port and Destination Port Fields..........................................................163
Message Length Field........................................................................................163
Checksum Field................................................................................................163
Operation..........................................................................................................163
Applications......................................................................................................164
The DNS.....................................................................................................................164
The Domain Name Structure................................................................................165
The Domain Name Tree........................................................................................165
The Name Resolution Process..............................................................................166
Data Flow..........................................................................................................166
Time Consideration..........................................................................................168
DNS Records..........................................................................................................168
Checking Records..................................................................................................169
Diagnostic Tools.........................................................................................................170
Ping........................................................................................................................170
Operation..........................................................................................................170
Implementation................................................................................................170
Using Windows NT Ping...................................................................................171
Traceroute..............................................................................................................173
Operation..........................................................................................................174
Using Windows Tracert.....................................................................................174
Tracing a Route.................................................................................................175
Applications......................................................................................................176
NSLOOKUP............................................................................................................177
Operation..........................................................................................................177
Viewing the SOA Record..................................................................................179
Protecting Server Information..........................................................................179
Finger.....................................................................................................................179
Format...............................................................................................................180
Security Considerations....................................................................................181
Applications......................................................................................................181
6 Security........................................................................................................183
Security Risks.............................................................................................................183
Architecture...........................................................................................................184
The Role of the SSID.............................................................................................184
Insertion Attacks....................................................................................................186
Monitoring Attacks................................................................................................186
Masquerade............................................................................................................188
xiii
Broadcast Monitoring............................................................................................191
Denial-of-Service Attacks........................................................................................192
Other Attack Methods...........................................................................................193
Exploiting File Sharing.....................................................................................193
SNMP Community Names................................................................................193
Accessing the Management Console................................................................194
Encryption Attacks............................................................................................194
Theft of Hardware............................................................................................194
Understanding WEP....................................................................................................196
Overview...............................................................................................................196
Setup Example.......................................................................................................197
Cipher Operation..................................................................................................197
RC4........................................................................................................................198
Algorithm Operation.........................................................................................198
WEP Key Definition...............................................................................................199
Authentication Methods.............................................................................................200
Open Authentication.........................................................................................200
Shared Key........................................................................................................200
MAC Address.....................................................................................................201
Vulnerabilities........................................................................................................201
The IV...............................................................................................................202
Attack Methods.................................................................................................202
Using the IV......................................................................................................203
Enhancing Wireless Security......................................................................................204
MAC Address-Based Authentication.......................................................................204
Use Dynamic WEP Keys........................................................................................204
LEAP Authentication..............................................................................................205
Using Secure Sockets.............................................................................................206
The VPN Solution..................................................................................................206
Bar Code Authentication.......................................................................................206
The IEEE 802.1x Standard.....................................................................................207
Overview..........................................................................................................207
Cisco Implementation......................................................................................208
Orinoco Implementation..................................................................................209
Router Access Control...........................................................................................209
Shielding................................................................................................................210
7 Working with Vendor Products..............................................................213
Agere Systems Orinoco Wireless Kit..........................................................................213
Client Setup...........................................................................................................213
Installation Software.........................................................................................214
Client Manager..................................................................................................214
Adjusting the Configuration.............................................................................217
Network Name.................................................................................................218
Security Setting.................................................................................................219
Power Management..........................................................................................220
TCP/IP Behavior...............................................................................................221
Setting Up the Residential Gateway......................................................................222
The Welcome Screen........................................................................................222
RG Identification...............................................................................................223
Specifying the Internet Connection.................................................................224
Settings Summary.............................................................................................225
Network Topology............................................................................................226