March 2001

Filtering Packets with iptables

by Joe "Zonker" Brockmeier

My initial plan for this column was to cover the use of iptables. However, after reading questions sent to the Netfilter mailing list, and some of the questions I ran across on various forums, I decided to spend a little more time on the basics of compiling a kernel and installing iptables. While many folks who are interested in using iptables are probably Linux gurus already, there are probably an equal number of novice Linux users who would benefit from starting at the beginning.

This month and next month, I'm going to take a look at filtering packets with iptables, the replacement for ipchains in the 2.4 Linux kernel. This month, I will deal with the basics of getting iptables up and running, and next month I'll explore using iptables in detail.

What Is iptables?

There are two components to iptables: the kernel modules and the user interface application. Support for iptables must be compiled into the Linux kernel, or as a loadable module; then there are several components that handle various tasks, such as masquerading, port forwarding, or packet filtering.