Firewall Fundamentals
暫譯: 防火牆基礎知識

Table of Contents

      Introduction

Part 1      Introduction to Firewalls3

Chapter 1 Introduction to Firewalls

What Is a Firewall?

What Can Firewalls Do?

     Firewalls Manage and Control Network Traffic

     Firewalls Authenticate Access

     Firewalls Act as an Intermediary

     Firewalls Protect Resources

     Firewalls Record and Report on Events

What Are the Threats?

     Targeted Versus Untargeted Attacks

     Viruses, Worms, and Trojans

     Malicious Content and Malware

     Denial of Service

     Zombies

     Compromise of Personal Information and Spyware

     Social Engineering

     New Attack Vectors

     Insecure/Poorly Designed Applications

What Are the Motives?

Security Policies

     Examples of Security Policies

     Firewalls and Trust

Determining If You Need a Firewall

Summary

Chapter 2 Firewall Basics

Firewall Taxonomy

     Personal Firewalls

     Network Firewalls

Firewall Products

     Software Firewalls

     Appliance Firewalls

     Integrated Firewalls

Firewall Technologies

     Personal Firewalls

     Packet Filters

     NAT Firewalls

     Circuit-Level Firewalls

     Proxy Firewalls

     Stateful Firewalls

     Transparent Firewalls

     Virtual Firewalls

Open and Closed Source Firewalls

Summary

Chapter 3 TCP/IP for Firewalls

Protocols, Services, and Applications

     The OSI Model

     The Department of Defense (DoD) Model

     How Firewalls Use Protocols, Applications, and Services

Internet Protocol (IP)

     IP Packet Structure

     The IP Packet Header

     Bad IP Packets

Transmission Control Protocol (TCP)

     TCP Segment Structure

     TCP Segment Header

     Bad TCP

User Datagram Protocol (UDP)

     UDP Message Structure

     UDP Datagram Header

     Bad UDP

Internet Control Message Protocol (ICMP)

     ICMP Message Structure

     Bad ICMP

Addressing in IP Networks

     Physical Addresses

     Logical Addresses

     IP Addressing

     Subnets

     IPv6

Network Address Translation (NAT)

NAT Implementations

     NAT and IPsec: The Issues and the Solutions

Broadcast and Multicast

IP Services

IP Routing

     Types of Routing

     How the IP Routing Process Works

     Different Classes of Routing Protocols

     Common Routing Protocols

Applications Using IP

     Common Applications Using IP

     Less-Common Applications Using IP

     Protocols Used to Implement Security

Summary

Part II     How Firewalls Work

Chapter 4 Personal Firewalls: Windows Firewall and Trend Micro’s PC-cillin

Windows Firewall and Windows XP

     How Windows Firewall Works

     Configuring Windows Firewall

     Windows Firewall Features

     Windows Firewall Checklist

Trend Micro’s PC-cillin Firewall Feature

     PC-cillin Requirements

     How the Trend Micro Firewall Works

     Configuring the Trend Micro Firewall

     Trend Micro Firewall Features

     Trend Micro Firewall Checklist

Summary

Chapter 5 Broadband Routers and Firewalls

How Broadband Routers and Firewalls Work

Linksys Broadband Routers/Firewalls

     Security and Filtering Features

     Routing Features

     Management and Administration Features

     Miscellaneous Features

Linksys Requirements

How the Linksys Router/Firewall Works

     Filtering Traffic from External Sources

     Filtering Traffic from Internal Sources

Configuring Linksys

     Configuring Basic Setup

     Configuring Security

     Configuring Applications & Gaming

     Configuring Administration

Linksys Checklist

Summary

Chapter 6 Cisco PIX Firewall and ASA Security Appliance

PIX/ASA Features

Choosing Between the PIX and the ASA

Cisco PIX Firewall and ASA Models

     SOHO Solution

     Medium- to Large-Office Solution

     Enterprise Office and Service Provider Solution

How the PIX/ASA Firewall Works

     Firewall Security Policy

     Firewall Modes of Operation

     Stateful Inspection

Configuring the Cisco PIX/ASA

     Assigning IP Addresses to the Firewall Interfaces

     Configuring the Firewall Name, Domain Name, and Passwords

     Configuring the Firewall Routing Settings

     Configuring the Firewall for Remote Management Access

     Configuring NAT Settings for Outbound Access

     Configuring the ACLs

     Configuring Logging on the Firewall

PIX/ASA Checklist

Summary

Chapter 7 Linux-Based Firewalls

NetFilter Features

NetFilter Requirements

How NetFilter Works

Configuring NetFilter

     IPTables Command-Line Tool

     Firewall Builder

     Firestarter

     Webmin

NetFilter Checklist

Summary

Chapter 8 Application Proxy Firewalls

Application Layer Filtering

     How Application Filtering Works

     The Difference Between Application Filtering and Deep Packet Inspection

Proxy Server Functionality

Limitations of Application Proxy Firewalls

Microsoft ISA Server 2004 Firewall

     Microsoft ISA Server 2004 Features

     Microsoft ISA Server 2004 Requirements and Preparation

     How the Microsoft ISA Server 2004 Firewall Works

     Microsoft ISA Server 2004 Checklist

Summary

Chapter 9 Where Firewalls Fit in a Network

Different Types of Office Requirements

     Central Office

     Remote Office

Single-Firewall Architectures

     Internet Firewall with a Single DMZ

     Internet Firewall with Multiple DMZs

     Internet-Screening Firewall (No DMZ)

Dual-Firewall Architecture

The Firewall System

     Single-Firewall System

     Dual-Firewall System

Where Personal/Desktop Firewalls Fit in a Network

Where Application Firewalls Fit in a Network

Firewalls and VLANs

     Virtual Firewalls

Using Firewalls to Segment Internal Resources

     Protecting Sensitive Internal Resources

     Protecting from WAN or Remote-Access Requests

     Protecting Individual Internal Resources

     Be Realistic When Implementing Internal Firewalls

High-Availability Firewall Designs

Summary

Part III    Managing and Maintaining Firewalls

Chapter 10 Firewall Security Policies

Written Security Policies

     The Difference Between Policies, Standards, Guidelines, and Procedures

     Security Policy Format

     Common Security Policies

     Firewall Security Policy

Firewall Policies/Rulesets

     Ingress Filters

     Egress Filters

     Management-Access Ruleset

Summary

Chapter 11 Managing Firewalls

Default Passwords

Maintaining the Underlying Platform

Firewall Management Interface

     Managing Firewalls with a CLI

     Managing Firewalls with a GUI

     Interface Preference

Management Access

     In-Band Management

     Out-of-Band Management

     Telnet vs. SSH

     HTTP vs. HTTPS

Common Firewall Management Tasks

     Initial Configuration

     Modifying the Configuration

     Updating the Firewall Software

Summary

Chapter 12 What Is My Firewall Telling Me?

Firewalls and Logging

     The Syslog Protocol

     Proprietary Logging Methods

     Why Logging Is Important

Firewall Log Review and Analysis

     What to Look for in Firewall Logs

     Cisco Secure PIX Firewall Syslog Event Baseline

Firewall Forensics

     The Value (or Not) of IP Addresses

     Deciphering Port Numbers

     Securing the Firewall

Summary

Chapter 13 Troubleshooting Firewalls

Developing a Troubleshooting Checklist

     Step 1: Verify the Problem Reported

     Step 2: Test Connectivity

     Step 3: Physically Check the Firewall

     Step 4: Check for Recent Changes

     Step 5: Check the Firewall Logs for Errors

     Step 6: Verify the Firewall Configuration

     Step 7: Verify the Firewall Ruleset

     Step 8: Verify That Any Dependent, Non-Firewall-Specific
Systems Are Not the Culprit

     Step 9: Monitor the Network Traffic

Basic Firewall Troubleshooting

     Troubleshooting Connectivity Through the Firewall

     Troubleshooting Connectivity to the Firewall

Advanced Firewall Troubleshooting

Troubleshooting Example

Summary

Chapter 14 Going Beyond Basic Firewall Features

Content Filtering

     Implementing a URL Filter

     Maintaining URL Filters

     What to Do If. . .

Performing Application Filtering

     Applications That Are Hard to Firewall

Intrusion Detection and Prevention

     Overview of IDS

Virtual Private Networks

     IPsec VPNs

     SSL VPNs

Summary

Endnotes

Part IV     Appendixes

Appendix A Firewall and Security Tools

Appendix B Firewall and Security Resources