How To Enable (NetBSD)

Introduced to NetBSD 2.0 as the package security/pflkm, in the base system from NetBSD 3.0 onwards (PF in NetBSD 5.1 is ~ OpenBSD 4.2)

Your kernel configuration file needs these non-default options:

pseudo-device  pf		# PF packet filter
pseudo-device  pflog		# PF log interface

Add to /etc/rc.conf:

pf=YES 
pflogd=YES

in /etc/lkm.conf:

/usr/lkm/pf.o - - - - BEFORENET