iptables

Website/Download: http://www.netfilter.org/projects/iptables/index.html
License: Freeware
OS: Linux
Latest Version:
Publisher's description:
iptables is the userspace command line program used to configure the Linux 2.4.x and 2.6.x IPv4 packet filtering ruleset. It is targeted towards system administrators.

Since Network Address Translation is also configured from the packet filter ruleset, iptables is used for this, too.