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by Brian Komar, Ronald Beekelaar,
and Joern Wettern, PhD
Firewalls
FOR
DUMmIES
‰
2ND EDITION
Firewalls For Dummies
®
, 2nd Edition
Published by
Wiley Publishing, Inc.
909 Third Avenue
New York, NY 10022
www.wiley.com
Copyright © 2003 by Wiley Publishing, Inc., Indianapolis, Indiana
Published by Wiley Publishing, Inc., Indianapolis, Indiana
Published simultaneously in Canada
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About the Authors
Brian Komar, B. Comm (Hons), a native of Canada, makes his living as a
Public Key Infrastructure (PKI) consultant, speaker, author, and trainer. Brian
speaks at conferences around the world on network design and security
topics. His consulting practice focuses on PKI design and architecture pro-
jects and on research assignments specializing in interoperability between
different vendors’ security products. In his spare time, Brian enjoys traveling
and biking with his wife Krista and sharing a fine bottle of wine (or more)
with his good friends.
Ronald Beekelaar, M.Sc., a native of The Netherlands, makes his living as a net-
work security consultant, author, and trainer. Ronald frequently trains network
administrators on network design and enterprise security topics. He writes
articles for several computer magazines, mostly about operating systems and
security issues. Ronald lives in Utrecht, The Netherlands, with his wife Kim.
They enjoy traveling abroad. If they find the time, they often travel to European
cities, especially London, to see a theater show and visit museums.
Joern Wettern, Ph.D., a native of Germany, is a network consultant and
trainer. Joern has also developed a range of training materials for a large soft-
ware publisher, and these materials are used to train thousands of network
administrators around the world. He frequently travels to several continents
to speak at computer conferences. Joern is paranoid enough to use an enter-
prise-class firewall to connect his home network. Somehow, he still manages
to enjoy the occasional sunny day and the many rainy ones in Portland,
Oregon, where he lives with his wife Loriann and three cats. In his spare time,
of which there is precious little, Joern and his wife hike up the mountains of
the Columbia Gorge and down the Grand Canyon. You can also find him
attending folk music festivals and dancing like a maniac. Joern’s latest project
is to learn how to herd his cats — without much success thus far.
The authors can be reached at FirewallsForDummies@hotmail.com.
Dedication
To Loriann, Krista, and Kim, and our parents.
Author’s Acknowledgments
This second edition would not have been possible without a large number of
people, especially the good folks at Wiley. We want to thank Byron Hynes for
being an excellent technical editor, and especially the humor he contributed
to the project. Melody Layne for pulling us together for another run at the
content, Paul Levesque for his insights on the content, and Rebekah Mancilla
for her editorial assistance.
Beyond the Wiley crew, we received help from firewall vendors who made it
possible for us to cover a number of different products and helped us with
issues that came up during the writing of the book. We would like to espe-
cially thank the ISA Server and PKI teams at Microsoft and Check Point for
providing an evaluation copy of FireWall-1 NG.
Finally, not a single chapter of this book would have been possible without
our spouses, who were willing to let us work on this project and thus are the
real heroes in this story.
Publisher’s Acknowledgments
We’re proud of this book; please send us your comments through our online registration form
located at
www.dummies.com/register/.
Some of the people who helped bring this book to market include the following:
Acquisitions, Editorial, and Media
Development
Project Editor: Paul Levesque
(Previous Edition: Linda Morris)
Acquisitions Editor: Melody Layne
Copy Editor: Rebekah Mancilla
Technical Editor: Byron Hynes
Editorial Manager: Leah Cameron
Media Development Manager:
Laura VanWinkle
Media Development Supervisor:
Richard Graves
Editorial Assistant: Amanda Foxworth
Cartoons: Rich Tennant,
www.the5thwave.com
Production
Project Coordinator: Ryan Steffen
Layout and Graphics: Seth Conley,
Carrie Foster, Lauren Goddard,
Michael Kruzil, Tiffany Muth,
Shelley Norris, Lynsey Osborn,
Jacque Schneider
Proofreaders: Andy Hollandbeck, Angel Perez,
Kathy Simpson, Charles Spencer,
Brian Walls, TECHBOOKS Production
Services
Indexer: TECHBOOKS Production Services
Publishing and Editorial for Technology Dummies
Richard Swadley, Vice President and Executive Group Publisher
Andy Cummings, Vice President and Publisher
Mary C. Corder, Editorial Director
Publishing for Consumer Dummies
Diane Graves Steele, Vice President and Publisher
Joyce Pepple, Acquisitions Director
Composition Services
Gerry Fahey, Vice President of Production Services
Debbie Stailey, Director of Composition Services
Contents at a Glance
Introduction 1
Part I: Introducing Firewall Basics 7
Chapter 1: Why Do You Need a Firewall? 9
Chapter 2: IP Addressing and Other TCP/IP Basics 23
Chapter 3: Understanding Firewall Basics 47
Chapter 4: Understanding Firewall Not-So-Basics 71
Chapter 5: “The Key Is under the Mat” and Other Common Attacks 97
Part II: Establishing Rules 111
Chapter 6: Developing Policies 113
Chapter 7: Establishing Rules for Simple Protocols 121
Chapter 8: Designing Advanced Protocol Rules 143
Chapter 9: Configuring “Employees Only” and Other Specific Rules 163
Part III: Designing Network Configurations 169
Chapter 10: Setting Up Firewalls for SOHO or Personal Use 171
Chapter 11: Creating Demilitarized Zones with a Single Firewall 179
Chapter 12: Designing Demilitarized Zones with Multiple Firewalls 197
Part IV: Deploying Solutions Using
Firewall Products 211
Chapter 13: Using Windows as a Firewall 213
Chapter 14: Configuring Linux as a Firewall 233
Chapter 15: Configuring Personal Firewalls: ZoneAlarm, BlackICE,
and Norton Personal Firewall 249
Chapter 16: Microsoft’s Firewall: Internet Security and Acceleration Server 295
Chapter 17: The Champ: Check Point FireWall-1 Next Generation 331
Chapter 18: Choosing a Firewall That Meets Your Needs 357
Part V: The Part of Tens 365
Chapter 19: Ten Tools You Can’t Do Without 367
Chapter 20: Ten Web Sites to Visit 375
Appendix: Protocol Listings and More 383
Index 393
Table of Contents
Introduction 1
About This Book 2
How to Use This Book 2
What You Don’t Need to Read 2
Foolish Assumptions 2
How This Book Is Organized 3
Part I: Introducing Firewall Basics 3
Part II: Establishing Rules 3
Part III: Designing Network Configurations 4
Part IV: Deploying Solutions Using Firewall Products 4
Part V: The Part of Tens 4
Icons Used in This Book 5
Where to Go from Here 5
Part I: Introducing Firewall Basics 7
Chapter 1: Why Do You Need a Firewall? . . . . . . . . . . . . . . . . . . . . . . . .9
Defining a Firewall 9
The Value of Your Network 11
Get Yourself Connected 12
Modem dial-up connections 13
ISDN connections 14
DSL connections 14
Cable modems 15
T1 and T3 16
Address types 17
The need for speed and security 17
TCP/IP Basics 18
What Firewalls Do 19
What Firewalls Look Like 20
A firewall that fits 20
Network router 21
Appliance 21
Software-only firewalls 21
All-in-one tools 21
Rules, Rules, Everywhere Rules 22
Chapter 2: IP Addressing and Other TCP/IP Basics . . . . . . . . . . . . . . .23
How Suite It Is: The TCP/IP Suite of Protocols 24
Sizing up the competition 24
Networking for the Cold War: A very short history of TCP/IP 25
Peeling Away the Protocol Layers 26
The Numbers Game: Address Basics 28
URLs: How to Reference Resources 32
Understanding IP Addresses 33
1 and 1 is 10 33
What IP addresses mean 34
Private IP Addresses 36
Dissecting Network Traffic: The Anatomy of an IP Packet 37
Source address 37
Destination address 38
Transport layer protocol 38
Other stuff 38
The other Internet layer protocol: ICMP 38
Transport Layer Protocols 39
Staying connected: UDP and TCP 39
Ports are not only for sailors 40
Some ports are well known 41
Application Layer Protocols 42
HTTP 42
SMTP 43
POP3 43
DNS 43
Telnet 43
Complex protocols 44
FTP 44
Future protocols 45
The Keeper of the Protocols 45
Putting It All Together: How a Request Is Processed 46
Chapter 3: Understanding Firewall Basics . . . . . . . . . . . . . . . . . . . . . .47
What Firewalls Do (And Where’s the Fire, Anyway?) 48
Basic functions of a firewall 48
What a firewall can’t do 50
General Strategy: Allow-All or Deny-All 51
Packet Filtering 54
Filtering IP data 55
Stateful packet filtering 60
Network Address Translation (NAT) 62
Security aspects of NAT 63
Consequences of NAT 64
Application Proxy 65
Monitoring and Logging 68
Chapter 4: Understanding Firewall Not-So-Basics . . . . . . . . . . . . . . .71
Making Internal Servers Available: Static Address Mapping 73
Static IP address assignment 74
Static inbound translation 75
Filtering Content and More 76
Firewalls For Dummies, 2nd Edition
x
Detecting Intrusion 79
Detecting an intrusion in progress 80
Responding to an intrusion 81
Reacting to a security incident 82
Improving Performance by Caching and Load Balancing 83
Caching Web results 84
United we stand, dividing the load 86
Using Encryption to Prevent Modification or Inspection 88
Encryption and firewalls 88
Who are you: Authentication protocols 89
The S in HTTPS 90
IP and security: IPSec 91
Virtual Private Networks (VPNs) 92
Chapter 5: “The Key Is under the Mat” and Other
Common Attacks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .97
Intrusion Attacks: A Stranger in the House 97
Denial-of-service Attacks 99
When everyone is out to get you: Distributed DoS attacks 100
How Hackers Get In 101
The key is under the mat: Insecure passwords 100
Default configurations 101
Bugs 102
Back doors 104
It’s a zoo: Viruses, worms, and Trojan horses 105
Who are you? Man-in-the-middle attacks 106
Impersonation 107
Eavesdropping 107
Inside jobs 108
Other techniques 108
Can a Firewall Really Protect Me? 109
Are You Scared Yet? 110
Part II: Establishing Rules 111
Chapter 6: Developing Policies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .113
Defining an Internet Acceptable Use Policy 114
Defining a Security Policy 118
Setting a Security policy 118
Chapter 7: Establishing Rules for Simple Protocols . . . . . . . . . . . . .121
For Starters, Some Default Rules 123
Allowing Web Access 123
Configuring inbound firewall rules 125
Configuring outbound firewall rules 126
xi
Table of Contents
Finding Internet Resources 126
Providing name resolution to Internet-based clients 127
Providing Internet name resolution to internal clients 128
File Transfer Protocol (FTP) 131
Messaging and Conferencing 133
America Online (AOL) Messaging 133
MSN Messenger and Windows Messenger 134
NetMeeting 135
Thin Client Solutions 137
Citrix Metaframe 137
Windows Terminal Services 138
Internet Control Message Protocol (ICMP) 139
Chapter 8: Designing Advanced Protocol Rules . . . . . . . . . . . . . . . . .143
Rain, Sleet, Snow, and Firewalls: Getting the E-Mail Through 144
Answering the right questions 146
Allowing access to external mail services 147
Allowing access to internal mail services 148
Knock, Knock: Who Goes There? 149
RADIUS functionality 150
Configuring inbound RADIUS firewall rules 151
IPSec Encryption 152
When does IPSec fail? 154
What will the future bring? 155
Configuring a firewall to pass IPSec data 157
Let Me In: Tunneling through the Internet 158
Selecting a tunneling protocol 158
Using PPTP firewall rules 159
Using L2TP/IPSec firewall rules 160
Chapter 9: Configuring “Employees Only”
and Other Specific Rules . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .163
Limiting Access by Users: Not All Are Chosen 163
Filtering Types of Content 165
Filtering Other Content 166
Preventing access to known “bad” sites 166
Implementing Content Rating 167
Setting the Clock: Filtering on Date/Time 168
Part III: Designing Network Configurations 169
Chapter 10: Setting Up Firewalls for SOHO or Personal Use . . . . . .171
No-Box Solution: ISP Firewall Service 171
Single-Box Solution: Dual-Homed Firewall 172
Screened Host 173
Bypassing the screened host 174
Firewalls For Dummies, 2nd Edition
xii
[...]... firewall serves and the basics of configuring a firewall 2 Firewalls For Dummies, 2nd Edition About This Book We try to provide you with a book that can act as a reference guide for firewalls We don’t expect you to read the book from cover to cover but to look at specific topics that meet your needs Twenty chapters and an appendix cover all topics of firewalls and their implementation Just turn to the chapter... out about firewalls Sidebars and extra information included in the book provide additional information that can help you, but you don’t need to read them to use firewalls This additional information is marked with the Technical Stuff icon However, if you want that extra technical information, you now know where to find it! Foolish Assumptions When we sat down to come up with the outline for this book,... process of determining what protocols to allow in and out of your network If you don’t have guidelines for securing your network, coming up with a configuration for your firewall is almost impossible! 3 4 Firewalls For Dummies, 2nd Edition Part III: Designing Network Configurations Put on your helmets for a trip to the world of Demilitarized Zones (the computer kind, not the combat kind) Part III puts... Sharing: NAT for Dummies 218 Windows NT 4.0 221 Packet filtering 222 PPTP server 223 Windows 2000 224 Packet filtering 224 Network Address Translation (NAT) .227 L2TP and IPSec 229 Windows XP 230 Internet Connection Firewall (ICF) 231 Windows Server 2003 232 xiii xiv Firewalls For Dummies, 2nd Edition... organization firewall: These firewalls are designed to protect all the computers in an office of limited size that is in a single location Firewalls in this category have the capacity to screen network traffic for a limited number of computers, and the reporting and management capabilities are adequate for this function ߜ Enterprise firewall: Enterprise firewalls are appropriate for larger organizations,... of Contents, find a topic that interests you, and go to that chapter If you’re looking for configuration details for specific firewalls, jump to Part IV where we provide detailed steps on how to install and configure popular firewall products used today If you’re just looking for tips on how to configure a firewall for specific protocols, Parts II and III look at simple and advanced protocol rules in... memorize a topic related to firewalls Tips provide you with inside information on how to quickly configure a rule or get past a common hurdle when designing firewalls Where to Go from Here You have the book in your hand, and you’re ready to get started Feel free to turn to any topic in the book that interests you! Look in the Table of Contents for the topic that drew your interest to firewalls If you’re not... to firewalls If you’re not curious about any specific topic but just want an overview, turn the page and start with Part I Either way, enjoy yourself and let us help you learn about firewalls! 5 6 Firewalls For Dummies, 2nd Edition Part I Introducing Firewall Basics F In this part irewalls — who needs ’em? Well it turns out, most of us do If you or your company is connected to the Internet, you may... nowhere to be found; for them the problem had been solved — the virus was gone For everyone else the problem had just started ߜ Hijacked computer: Imagine that someone broke into your computer and used it for his own purposes If your computer is not used much anyway, this may not seem like a big deal However, now imagine that the intruder uses your computer for illegitimate purposes For example, a hacker... computer to another using TCP/IP includes information on what IP address the data comes from and what IP address it is being sent to TCP/IP defines the methods that computers connected to the Internet use to transmit information This includes dividing this information in small manageable chunks called packets Each packet contains header information and data Most firewalls examine the packet header to determine . by Brian Komar, Ronald Beekelaar, and Joern Wettern, PhD Firewalls FOR DUMmIES ‰ 2ND EDITION Firewalls For Dummies ® , 2nd Edition Published by Wiley Publishing, Inc. 909 Third Avenue New. Port Listing 384 Index 393 Firewalls For Dummies, 2nd Edition xvi Introduction W elcome to Firewalls For Dummies, a book written to help the average Joe understand how firewalls work and how to. Wiley, the Wiley Publishing logo, For Dummies, the Dummies Man logo, A Reference for the Rest of Us!, The Dummies Way, Dummies Daily, The Fun and Easy Way, Dummies. com and related trade dress are
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