Building a Firewall with IP Chains
Ip chains is a very powerful tool that allows you to create many complex rules in order to protect your network. Just for fun, I built a small C program to build simple firewall scripts and simplify the rc.d process. It is open source and available at linuxgo.persogo.com.br/ipchains.html. Good places to get more information on how to build great scripts are the HOWTOs (see Resources). Read them before you start to build your own firewall scripts.