The netfilter/iptables project is the Linux 2.4.x / 2.5.x firewalling subsystem. It delivers you the functionality of packet filtering (stateless or stateful), all different kinds of NAT (Network Address Translation) and packet mangling.
If you are running a recent Linux system (Kernel 2.4.x or above) on a router, you can use netfilter/iptables for all kinds of firewalling, NAT or other advanced packet processing.
