The Shoreline Firewall, more commonly known as "Shorewall", is a high-level tool for configuring Netfilter. You describe your firewall/gateway requirements using entries in a set of configuration files. Shorewall reads those configuration files and with the help of the iptables utility, Shorewall configures Netfilter to match your requirements. Shorewall can be used on a dedicated firewall system, a multi-function gateway/router/server or on a standalone GNU/Linux system. Shorewall does not use Netfilter's ipchains compatibility mode and can thus take advantage of Netfilter's connection state tracking capabilities. http://www.shorewall.net/
Shorewall is a great firewall package for Linux it's, most distro's have packages available. What do you think about Shorewall? Do you have any other favorite firewall package.
Devil-Linux is a distribution which boots and runs completely from CD. The configuration can be saved to a floppy diskette or a USB pen drive. It was originally intended to be a dedicated firewall/router but now Devil-Linux can also be used as a server for many applications. Attaching an optional hard drive is easy, and many network services are included in the distribution.
Have you used any Linux distributions which are design to be used as a firewall or router? This article looks at the Devil-Linux distribution with some useful links to learn more about this Linux distro.
(The)Demilitarized zone, used to secure an internal network from external access. You can use Linux firewall to create DMZ easily. There are many different ways to design a network with a DMZ. The basic method is to use a single Linux firewall with 3 Ethernet cards. The following simple example discusses DMZ setup and forwarding public traffic to internal servers.
There's a little advanced know-how required here and he recommends a couple good firewalls to set up such functionality just in case this very useful guide doesn't fit the bill. If you are looking to set up a Linux Demilitarized zone a couple of options include EnGarde, IpCop and others.