you need a powerful firewall in Linux use iptables

firestarter

Firestarter is an Open Source visual firewall program. The software aims to combine ease of use with powerful features, therefore serving both Linux desktop users and system administrators.

We strongly believe that your job is to make the high level security policy decisions and ours is to take care of the underlying details. This is a departure from your typical Linux firewall, which has traditionally required arcane implementation specific knowledge.