You might want to check out the January issue of SysAdmin Magazine. They had an interesting article on running a firewall using ipchains on Redhat Linux.

RedDog
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...We will have peace, when you and all your works have perished -- and the works of your dark master to whom you would deliver us. You are a liar, Saruman, and a corrupter of men's hearts. -- Theoden in The Two Towers --