gibraltar
I have to set up a firewall (bridged network – transparent firewall). I am using a Debian-based distribution from Austria (no, not where the kangaroos live ;)) called Gibraltar. Main documentation can be found in the mailinglist-archiv, Rene Mayrhofer from Gibraltar writes really nice and helpfull stuff. Gibraltar is really a great piece of Software! I should take some ideas for my own project called grml.