"Between 2000 and mid-2008, I've read and reviewed nearly 250 technical books. I've also written several books, so I believe I can recognize a great book when I see it. Linux Firewalls is a great book."
—Richard Bejtlich, TaoSecurity.com, from the foreword to Linux Firewalls

View a sample chapter, Chapter 10: Deploying fwsnort

System administrators need to stay ahead of new security vulnerabilities that leave their networks exposed every day. A firewall and an intrusion detection systems (IDS) are two important weapons in that fight, enabling you to proactively deny access and monitor network traffic for signs of an attack.

Linux Firewalls discusses the technical details of the iptables firewall and the Netfilter framework that are built into the Linux kernel, and it explains how they provide strong filtering, Network Address Translation (NAT), state tracking, and application layer inspection capabilities that rival many commercial tools. You'll learn how to deploy iptables as an IDS with psad and fwsnort and how to build a strong, passive authentication layer around iptables with fwknop.

Concrete examples illustrate concepts such as firewall log analysis and policies, passive network authentication and authorization, exploit packet traces, Snort ruleset emulation, and more with coverage of these topics:

• Passive network authentication and OS fingerprinting
• iptables log analysis and policies
• Application layer attack detection with the iptables string match extension
• Building an iptables ruleset that emulates a Snort ruleset
• Port knocking vs. Single Packet Authorization (SPA)
• Tools for visualizing iptables logs

Perl and C code snippets offer practical examples that will help you to maximize your deployment of Linux firewalls. If you're responsible for keeping a network secure, you'll find Linux Firewalls invaluable in your attempt to understand attacks and use iptables—along with psad and fwsnort—to detect and even prevent compromises.

Visit the book's companion site for supporting files, downloads, errata, and more.

Michael Rash is a security architect with Enterasys Networks, Inc., where he develops the Dragon intrusion and prevention system. He is a frequent contributor to open source projects and the creator of psad, fwknop, and fwsnort. Rash is an expert on firewalls, intrusion detection systems, passive OS fingerprinting, and the Snort rules language. He is co-author of Snort 2.1 Intrusion Detection (Syngress, 2004) and author of Intrusion Prevention and Active Response (Syngress, 2005), and he has written security articles for Linux Journal, Sys Admin magazine, and ;login:.