Wireless Networks dor Dummies phần 1 ppsx

by Barry Lewis and Peter T. Davis
Wireless
Networks
FOR
DUMmIES
‰
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by Barry Lewis and Peter T. Davis
Wireless
Networks
FOR
DUMmIES
‰
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Wireless Networks For Dummies
®
Published by
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Copyright © 2004 by Wiley Publishing, Inc., Indianapolis, Indiana
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About the Author
Barry D. Lewis (CISSP, CISM) has been in the information technology sector
for 35 years, specializing in information security since 1980. He co-founded
Cerberus Information Security Consulting in 1993 and was elevated to
President of the firm shortly thereafter. He served as Secretary and then Vice
President of the ISC(2) organization, past-President of the Toronto ISSA, and
Chairperson of the Eastern Canada ACF2 Users Group. Barry is listed in the
International Who’s Who of Entrepreneurs. Mr. Lewis lectures worldwide on
computer security and audit issues and was honored with the Best Speaker
Award at the annual Computer Associates Enterprise Wide Security & Audit
conference (ESAC), one of North America’s largest security conferences. Mr.
Lewis has written and co-authored numerous articles and seven books,
including Computer Security For Dummies, and Teach Yourself Windows 2000
Server in 21 Days. He lives near Toronto with his wife Elizabeth and son
Derek.
Peter T. Davis (CISA, CMA, CISSP, CWNA, CCNA, CMC, CISM) founded
Peter Davis+Associates (a very original name) as a firm specializing in the
security, audit, and control of information. A 29-year information systems
veteran, Mr. Davis’s career includes positions as programmer, systems ana-
lyst, security administrator, security planner, information systems auditor,
and consultant. Peter also is the past President and founder of the Toronto
ISSA chapter, past Recording Secretary of the ISSA’s International Board, and
past Computer Security Institute Advisory Committee member. Mr. Davis has
written or co-written numerous articles and 10 books, including Computer

Security For Dummies and Securing and Controlling Cisco Routers. Peter was
also the technical editor for Hacking For Dummies and Norton Internet Security
For Dummies. Peter is listed in the International Who’s Who of Professionals. In
addition, he was only the third Editor in the three-decade history of EDPACS,
a security, audit and control publication. He finds time to be a part-time lec-
turer in data communications at Seneca College (
cs.senecac.on.ca). He
lives with his wife Janet, daughter Kelly, two cats, and a dog in Toronto,
Ontario.
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Dedication
To my wife Elizabeth, who puts up with far more than I have a right to expect.
— Barry
To all my friends and enemies. Hopefully, the first group is bigger than the
second.
— Peter
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Author’s Acknowledgments
We’d like to offer special thanks to Pat O’Brien, who started this rolling. Peter
worked as the technical editor for Pat on Hacking For Dummies. Thanks for
passing on Melody’s name.
Thanks to Melody Layne, acquisitions editor, for pitching the book to the edi-
torial committee and getting us a contract. Much appreciated.
Thanks to Becky Huehls, who started us out on this project as editor but
wisely got herself re-assigned. Thanks to Kelly Ewing for picking up the ball
and running with it after Becky. Unfortunately, Kelly fumbled it, but Colleen
Totz was able to struggle with it over the goal line.
Dan DiNicolo, technical editor, is commended for his diligence in reviewing

the material. Thanks, Dan.
Peter would like to thank Kevin Beaver, Ken Cutler, Gerry Grindler, Ronnie
Holland, Carl Jackson, Ray Kaplan, Kevin Kobelsky, Carrie Liddie, Dexter
Mills Jr., and Larry Simon for responding to a request for wireless informa-
tion. Thanks for answering the call for help. The provided information shows
in this book.
Barry would like to thank his co-author Peter. Always a pleasure, sir. He
would also like to acknowledge Craig McGuffin and John Tannahill who are
always there for him, as friends and business associates , and never fail to
lend a helping hand.
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Publisher’s Acknowledgments
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Contents at a Glance
Introduction 1
Part I: Planning and Acquiring Your Network 7
Chapter 1: Removing the Tethers: Entering the Wireless World 9
Chapter 2: If You Fail to Plan, You Plan to Fail 25
Chapter 3: Matching Wireless Technologies to Your Plan 47

Part II: Implementing Your Wireless Network 59
Chapter 4: Getting a Quick Start with Wireless Personal Area Networks 61
Chapter 5: Moving On to a Wireless LAN: Your Wireless Access Point 83
Chapter 6: Connecting Your Clients 103
Chapter 7: Building the Multi-Zone Network 121
Chapter 8: Using Wireless on the Road to Connect to the Office 133
Part III: Using Your Network Securely 147
Chapter 9: Considering a Deadbolt: Understanding the Risks of
Wireless Networks 149
Chapter 10: Designing a Secure Network 169
Chapter 11: Maintaining Network Security 185
Chapter 12: Secure Wireless Access with Virtual Private Networking 209
Part IV: Keeping Your Network on the Air —
Administration and Troubleshooting 229
Chapter 13: Problems with Keeping on the Air 231
Chapter 14: Bridging Networks to Manage Coverage 249
Chapter 15: Dealing with Network Throughput Issues 265
Chapter 16: It’s Ten O’Clock: Do You Know Where Your Access Points Are? 283
Part V: The Part of Tens 303
Chapter 17: Ten Administrator Tools and What They Do 305
Chapter 18: Top Ten Ways to Secure Your Network 313
Chapter 19: Ten Ways Wireless Is Used in Business 327
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Part VI: Appendixes 339
Appendix A: Industry Trade Associations 341
Appendix B: Wireless Standards 347
Appendix C: The Fundamentals of Radio Frequency 353
Index 371
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Table of Contents

Introduction 1
About This Book 2
How to Use This Book 3
How This Book Is Organized 3
Part I: Planning and Acquiring Your Network 3
Part II: Implementing Your Wireless Network 4
Part III: Using Your Network Securely 4
Part IV: Keeping Your Network on the Air —
Administration and Troubleshooting 4
Part V: The Part of Tens 5
Part VI: Appendixes 5
Icons Used in This Book 5
Where to Go from Here 6
Part I: Planning and Acquiring Your Network 7
Chapter 1: Removing the Tethers: Entering the Wireless World . . . . .9
Understanding the Risks and Rewards of Going Wireless 10
What you risk 10
The benefits you gain 11
Applications of Wireless Networks 11
Sorting Out the Nets: Do I Need a WPAN, WLAN, or WMAN? 12
Let’s get personal: WPAN 13
The holy grail of wireless networking: WLAN 14
Where the rubber hits the road: WMAN 15
Using Wireless Networks 16
Accessing networks 16
Extending the network 17
Connecting buildings 17
Going mobile 18
Getting mail on the road 19
Turning a Notion into a Network 20

Planning your wireless network 20
Installing your wireless network 20
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Configuring a wireless network 21
Staying secure in the wireless world 22
Administering and maintaining a wireless network 22
Convergence of Wireless Technologies —
What Will the Future Hold? 23
Chapter 2: If You Fail to Plan, You Plan to Fail . . . . . . . . . . . . . . . . . . .25
Evaluating Your Wireless Needs 25
What is my environment? 26
What is my budget? 26
How many clients do I expect? 27
Where will they want to access the network? 28
What does the data look like? 28
What technology do I want to use? 29
Do I need to protect the data? 31
What coverage do I need? 31
Preparing for a Site Survey 32
Analyzing your facility 33
Working with existing networks 33
Area coverage 34
Purpose and business requirements 36
Bandwidth and roaming requirements 37
Available resources 37
Security needs analysis 38
Developing a site survey checklist 38
Using Site Survey Equipment to Get It Right 39
Doing That Site Survey 41
Analyzing your indoor network 42

Analyzing your outdoor network 42
Calculating a link budget 42
Describing Your Final Plan in a Site Survey Report 45
Defining the business requirements and methodology 45
Documenting the requirements 46
Chapter 3: Matching Wireless Technologies to Your Plan . . . . . . . . .47
Choosing the Right Networking Hardware 47
Are You Being Served? IBSS, BSS, and ESS 50
Selecting the Wireless Mode 51
Considering ad hoc mode 51
Using infrastructure mode 52
Wireless Networks For Dummies
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Gearing Up to Send and Receive Signals 52
Frequencies and spectrums 53
Get the right antennae 54
Introducing the zone — a wireless diet 56
Understanding and Using Layer 2 and 3 Concepts 57
Part II: Implementing Your Wireless Network 59
Chapter 4: Getting a Quick Start with
Wireless Personal Area Networks . . . . . . . . . . . . . . . . . . . . . . . . . . . . .61
Understanding IrDA 61
Installing infrared devices 63
Using IrDA to transfer data 64
Securing IrDA 66
Understanding Bluetooth 67
Adding Bluetooth capabilities 71
Securing Bluetooth 74
Protecting Bluetooth networks 75

IrDA and Bluetooth Comparison 82
Chapter 5: Moving On to a Wireless LAN:
Your Wireless Access Point . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .83
Parts Is Parts — Do You Have Them All? 83
Connecting and Configuring Your Access Point 84
Connecting the access point 85
Configure your browser 86
Changing the default network settings 87
Initial Setup and Testing 88
Deciding on initial setup options 88
Performing the advanced setup functions 92
Back up your work 94
Turning Off the Defaults 94
Changing the password 95
Changing the access point name 95
Changing security options 96
Understanding the other options 98
Configuration and setup of a Cisco Aironet 1200 99
Testing the Signal 102
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Chapter 6: Connecting Your Clients . . . . . . . . . . . . . . . . . . . . . . . . . . . .103
Adding Hardware to the PC 104
Peripheral Component Interconnect (PCI) 105
Universal Serial Bus (USB) 106
Ethernet client adapter 106
The final decision 107
Wireless print server 108
Installing the Wireless Hardware 109

Upgrading the firmware or software 109
Important guidelines for upgrading 111
Configuring the Client’s Operating System 112
Configuring Windows XP Professional clients 112
Configuring Windows 2000 clients 114
Configuring Mac OS clients 117
Configuring your Centrino systems 118
Configuring Linux and FreeBSD Clients 119
Making Sure the Connection Works 120
Chapter 7: Building the Multi-Zone Network . . . . . . . . . . . . . . . . . . .121
Roaming Around with a Wireless Machine 121
Wireless roaming standards 122
Connectivity issues as you move around 126
Reassociation — Getting back together as you move
from AP to AP 129
Load Balancing — Are All Zones Used Equally? 131
Chapter 8: Using Wireless on the Road
to Connect to the Office . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .133
Spontaneous Communities: Ad Hoc Networks 133
Wi-Fi Warriors on the Road 134
Wireless at the airport 135
Wireless in hotels 136
E-Mailing Wirelessly with Microsoft Exchange 137
Setting up POP access 138
Connecting directly to Exchange 140
Wireless Hot Spots: What’s New Around the World? 144
In the air 145
New ideas for wireless network attacks 146
Wireless Networks For Dummies
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Part III: Using Your Network Securely 147
Chapter 9: Considering a Deadbolt: Understanding
the Risks of Wireless Networks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .149
Risks to the Network 149
Going to war: War nibbling, war driving, war flying,
and war chalking 150
A roguish WLAN 156
Open broadcast of SSIDs 156
Jamming 157
Signal loss 158
Risks to Your Users 160
Target profiling 160
Identity theft 160
Lack of authentication 161
Default passwords are de fault 162
Risks to Your Data 163
You call that encryption?! 164
Accidental associations 165
Eavesdropping 165
Man-in-the-middle attacks 166
Hijacking 166
Chapter 10: Designing a Secure Network . . . . . . . . . . . . . . . . . . . . . .169
Security as a Cost of Doing Business 170
Developing a Security Architecture 171
Developing a Wireless Security Policy 173
Developing Wireless Security Standards 175
Developing Wireless Security Best Practices 176
General best practices 176
Access point best practices 177

Password best practices 178
SSID best practices 178
Authentication best practices 178
Encryption best practices 179
Client best practices 179
Network best practices 180
Managing Your Wireless Security Policy 181
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Designing a Secure Network 182
Performing a Risk Analysis 182
Chapter 11: Maintaining Network Security . . . . . . . . . . . . . . . . . . . . .185
Understanding Security Mechanisms 186
Three States of Authentication 187
Authentication 187
Protecting Privacy 189
Protecting Message Integrity 190
Filtering the Chaff 191
SSID filtering 191
MAC filtering 191
Protocol filtering 193
Using Encryption 193
Hip to WEP 194
WEP weaknesses 196
Attacking WEP 198
Key management problems 199
Protecting WEP Keys 200
Default WEP keys 200
Using WPA 202

AES-CCMP 204
Using Port Authentication 204
Using LEAP, PEAP, and other forms of EAP 206
EAP Questions 207
Chapter 12: Secure Wireless Access with
Virtual Private Networking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .209
Secure Access with a VPN 209
Defining the VPN 211
VPN considerations 213
Understanding tunneling 214
Deploying VPNs in WLANs 216
Wireless VLANs 217
Various Other Methods for Secure Access 218
Using Microsoft’s Point-to-Point Tunneling Protocol 218
Considering Layer 2 Tunneling Protocol 225
Using Windows IPSec 225
Oldies but goodies — SSH2 226
Who Is Doing the Talking? 228
Wireless Networks For Dummies
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Part IV: Keeping Your Network on the Air —
Administration and Troubleshooting 229
Chapter 13: Problems with Keeping on the Air . . . . . . . . . . . . . . . . . .231
Troubleshooting Redux 231
Am I in Your Fresnel Zone? 234
Multipath Interference 236
You Can’t Go That Far: Free Space Loss 238
Contention-Free Frames 239
Hidden Node — So Where Is It? 241

Managing Power 243
Power over Ethernet (PoE) 244
Calculating your Power Budget 245
Chapter 14: Bridging Networks to Manage Coverage . . . . . . . . . . . .249
Using That Site Survey 250
Bridges and Switches and Routers, Oh My! 250
Understanding Wireless Bridges 251
Using root mode 254
Using non-root mode 254
Using access point mode 255
Using repeater mode 255
Wireless Workgroup Bridge 255
Going to the Movies: A Bridge Too Far? 257
Building Hardware Bridges 258
Bridging the Gap: Getting Started 259
Troubleshooting Your Bridged Network 260
Building Network Bridges in Windows XP 260
Creating a network bridge 261
Troubleshooting a wireless bridge 262
Using Wireless Switches 262
Chapter 15: Dealing with Network Throughput Issues . . . . . . . . . . .265
Watching Traffic 265
Estimating network performance 266
Sniffing your traffic 272
Traffic management and analysis 277
Outsourcing your network management 278
Monitoring the Network for Trouble Spots 279
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Chapter 16: It’s Ten O’Clock: Do You Know Where Your
Access Points Are? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .283
Discovering the Extent of Your Wireless Network 283
Using programs that came with your operating system 284
Using utilities that came with your network adapter 284
Using war driving or network discovery tools 285
Using traffic management and analysis tools 286
Using network management tools 287
Using vulnerability testing software 289
Detecting Wireless Intrusion 291
Incident Response and Handling 299
Auditing Activities 300
Part V: The Part of Tens 303
Chapter 17: Ten Administrator Tools and What They Do . . . . . . . . . .305
Using Ethereal to Look at Traffic 306
Stumbling on Networks with NetStumbler 306
With Luck, You Can Find Networks with Kismet 308
Surfing for Networks with Wellenreiter 308
Using AirSnort to Obtain WEP Keys 309
Rooting Around with THC-RUT 309
Cracking Encryption with WEPCrack 310
Getting a MAC Address 310
Creating Sham Access Points with FakeAP 311
Let’s Sneak a Peek with AiroPeek, Shall We? 312
Chapter 18: Top Ten Ways to Secure Your Network . . . . . . . . . . . . . .313
Using the Highest Level of Encryption 314
Changing the Default SSID 315
Looking for Rogue WAPs 315
Disabling Ad Hoc Mode 317
Disabling SNMP or Select Strong String 317

Turning Down the Power 319
Securing WAPs with a Subnet and a Firewall 321
Using a WIDS 325
Disabling Wired Access from Public Areas 325
Hardening the Access Point and Clients 326
Wireless Networks For Dummies
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Chapter 19: Ten Ways Wireless Is Used in Business . . . . . . . . . . . . .327
Attending Meetings with Tablet PCs 327
Getting Your E-mail As You Wander the Building 329
Getting Corporate Access in the Lunchroom 329
Setting Up Wireless Conference Rooms 329
Querying Your Corporate Database 331
Keeping in Touch at the Airport 331
Maintaining a Presence While Having Coffee 332
Using Bluetooth Phones in Your Car 334
Accessing a Wireless Network in Your Hotel 335
Using the Phone to Check Your Stocks 338
Part VI: Appendixes 339
Appendix A: Industry Trade Associations . . . . . . . . . . . . . . . . . . . . . .341
Government Organizations 341
International Standards Organizations 342
Wireless-Related Organizations and Associations 343
Local Wireless Groups 345
Other Industry Associations 346
Appendix B: Wireless Standards . . . . . . . . . . . . . . . . . . . . . . . . . . . . .347
802.1x 347
802.11 348
802.11a 348

802.11b 348
802.11c 349
802.11d 349
802.11e 349
802.11f 349
802.11g 350
802.11h 350
802.11i 350
802.11j 350
802.11k 351
802.11n 351
802.15 351
802.16 352
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Appendix C: The Fundamentals of Radio Frequency . . . . . . . . . . . . .353
Radio Frequency 353
Behavior of Radio Waves 360
Gain 360
Loss 360
Reflection 361
Refraction 361
Diffraction 361
Scattering 361
Absorption 362
Free space loss 362
Fresnel zone 362
RF Units of Measure 362
Watt’s that, you say? 363

I hear ’bels 363
RF Mathematics 365
Calculating decibels 365
Calculating path loss 367
Calculating antenna length 367
Calculating coaxial cable losses 368
Calculating the Fresnel zone 368
Calculating the measurements for a home-grown antenna 370
Index 371
Wireless Networks For Dummies
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Introduction
R
ecently, a very knowledgeable speaker at a presentation for a wireless
vendor talked about wireless as ubiquitous. We would have to disagree.
Wireless is widespread, but it is not everywhere. But it is rapidly becoming
ubiquitous.
In about 1990, cell phone users carried around a phone that looked and felt
like a World War II walkie-talkie. You didn’t casually whip that baby out and
start a conversation. At that time, you either had a deep wallet, a big ego, or
a compelling need to talk to your mother. Now, depending on where you live
in the world, the cell phone provides better quality at a lower cost — and in a
much smaller form factor.
In about 1994, Wireless Local Area Network (WLAN) equipment manufacturers
sold gear that was comparable to the wireless phone market. The devices were
large and very expensive and provided poor bandwidth. You had to have a
compelling reason to spend the money on the low bandwidth. But that has
changed. In 2004, you can buy a reasonably priced laptop with onboard sup-
port for 802.11b and Bluetooth. You can add a fairly inexpensive 802.11a

and g PC Card and easily connect wirelessly and, if you have a Centrino-based
system or Microsoft Windows XP, somewhat seamlessly. The WLAN market
of today is analogous to the Ethernet market of the mid 1980s. In those years,
solutions were proprietary, and standards were being approved. Companies
were jockeying for position. Now, you would have difficulty finding a desktop
or laptop computer that does not come with Ethernet support. When we look
back from the future, we will see some parallels between 802.3 and 802.11
development.
Telephone companies have wrestled with the issue of the “last mile” for
a while. But forget the last mile; Bluetooth and IrDA provide the last foot.
Mice, keyboards, phones, PDAs, and other devices support Bluetooth for
wire replacement. When you have a Bluetooth-enabled printer, you no longer
need to hook up to the network to print one page or a contact.
Vendors are trying to get along with each other to develop standards so that
one day we can walk around with a phone, PDA, or laptop and connect to any
network, anywhere, anytime.
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We wrote this book for those of you who want to release your company from
its bondage. If you want to unfetter your clients so that they can access their
e-mail before getting on the red-eye to New York or Toronto, this book is for
you. If your desktop looks like spaghetti junction and you want to rid yourself
of all those wires, this book is for you. If you want to provide up-to-the-minute
stock quotes to the Chair of your company while she sits in the boardroom,
this book is for you. If you have a small to medium enterprise (SME) or busi-
ness (SMB) or a small office/home office (SOHO) and don’t want to rewire
(or pay someone to rewire) your office, this book is for you. If you have wire-
less at home and want to learn about features that you can expect for home
gear, this book is for you.
About This Book
Mark Twain once wrote, “Writing is easy. All you have to do is cross out

the wrong words.” So we have done the easy part for you. We crossed out
all the wrong words and came up with this book. What are left are the words
that will help you plan for, install, acquire, protect, manage, and administer
wireless networks from personal area to wide area.
We have started your journey by providing information on
ߜ Differentiating WPAN, WLAN, WMAN, and WWAN
ߜ Planning your wireless network
ߜ Doing a site survey
ߜ Using IrDA for transferring files
ߜ Using Bluetooth for wire replacement
ߜ Securing IrDA and Bluetooth
ߜ Acquiring the right equipment
ߜ Installing and configuring an access point
ߜ Acquiring and installing client hardware
ߜ Installing and configuring client software
ߜ Building a network to allow roaming
ߜ Connecting while on the go
ߜ Securing your WLAN
ߜ Understanding WEP, WPA, and RSN
ߜ Understanding EAP
2
Wireless Networks For Dummies
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