Linux Firewalls, Third Edition

Differences Between IPFW and Netfilter Firewall Mechanisms

Because iptables is so different from the previous ipchains, this book won't attempt to cover the older implementation.

The next section is written for the reader who is familiar with or is currently using ipchains. If iptables is your first introduction to Linux firewalling, you can skip ahead to the section “Netfilter Packet Traversal.”

If you are converting from ipchains, you'll notice several minor differences in the iptables syntax, most notably that the input and output network interfaces are identified separately. iptables is highly modularized, and the individual modules must occasionally be loaded explicitly. Logging is a rule target rather than a command option. Connection state ...