iptables 1.3.3-2ubuntu4 (i386 binary) in ubuntu dapper

 netfilter and iptables provide a Linux kernel framework for
 stateful and stateless packet filtering, network and port addresss
 translation, and other IP packet manipulation. The framework is the
 successor to ipchains.
 .
 netfilter and iptables are used in applications such as Internet
 connection sharing, firewalls, IP accounting, transparent proxying,
 advanced routing and traffic control.
 .
 iptables web site: http://www.iptables.org/