Chapter List

Introduction

Over the years, the open source community has excelled in creating firewall software that is ideally suited for networks of any size. Linux natively supports the ability to route and/or filter packets. Modern Linux systems use either Ipchains or Iptables to do this.

Iptables supports Linux kernel 2.4 and higher (it was first implemented in Linux kernel 2.3). For those still using Linux kernel 2.2, use Ipchains instead. The Iptables package supports packet masquerading and filtering functionality as found in the 2.3 kernel and later. This functionality is known as netfilter, which is what Iptables is based on. Therefore, in order to use Iptables, you must recompile the kernel so that netfilter is installed, and you must also install the Iptables package. This is found by clicking Networking Options IP: NetFilter Configuration.

Depending on your kernel version, you can use these applications to configure your Linux system to act as a router, which means that it ensures that packets are sent from one network to another. At this level, a Linux router does not examine or filter any traffic. It simply ensures that all traffic addressed to a remote network gets sent to...