High Quality Content by WIKIPEDIA articles! PF (Packet Filter, also written pf) is a BSD licensed stateful packet filter, a central piece of software for firewalling. It is comparable to iptables, ipfw and ipfilter. PF is developed on OpenBSD, but has been ported to many other operating systems including Mac OS 10.7 ‘Lion’, FreeBSD, NetBSD, DragonFly BSD and Debian GNU/kFreeBSD.