IPFilter, also called ipf is a packet filter, a software that can be used as a firewall or as a NAT to translate Internet addresses.
IPFilter has been written by Darren Reed since the early 1990s; Version 1.0 was released on 22 April 1993. IPFilter is active as open source software developed ( BSD-like license). Currently, the 5.1 series, which was published on May 9, 2010.
See also: pf, ipfw, iptables