BUILDING A WIRELESS NETWORK GILBERT HELD AUERBACH PUBLICATIONS A CRC Press Company Boca Raton London New York Washington, D.C. This edition published in the Taylor & Francis e-Library, 2005. “To purchase your own copy of this or any of Taylor & Francis or Routledge’s collection of thousands of eBooks please go to www.eBookstore.tandf.co.uk.” 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 This book contains information obtained from authentic and highly regarded sources. Reprinted material is quoted with permission, and sources are indicated. A wide variety of references are listed. Reasonable efforts have been made to publish reliable data and information, but the author and the publisher cannot assume responsibility for the validity of all materials or for the consequences of their use. 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Visit the Auerbach PublicationsW eb site at www.auerbach-publications.com © 2003 by CRC Press LLC Auerbach is an imprint of CRC Press LLC No claim to original U.S. Government works International Standard Book Number 0-8493-1271-X 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