This chapter covered the majority of features available in iptables—certainly, the features most commonly used. I’ve tried to give a general sense of the differences between Netfilter and IPFW, if for no other reason than to give you a "heads up" for the implementation differences that will appear in the following chapters. The modular implementation divisions of three separate major tables—filter, mangle, and nat—was presented. Within each of these major divisions, features were further broken down into modules that provide target extensions and modules that provide match extensions.
Chapter 4, "Building and Installing a Standalone Firewall," goes through a simple, standalone firewall example. Basic antispoofing, denial of service, and other fundamental rules are presented. The purpose of the chapter isn’t to present a general firewall for people to cut and paste for practical use, as much as to demonstrate the syntax presented in this chapter in a functional way.
Subsequent chapters are more specific. User-defined chains, firewall optimization, LAN, NAT, and multihomed hosts are covered separately, as are larger local network architectures.