OpenBSD Firewall/VPN Resources
Kyle Amon,  Page 32
OpenBSD
http://www.openbsd.org/

IP Filter
http://coombs.anu.edu.au/~avalon/

IP Filter HOWTO
http://www.obfuscation.org/ipf/

Packet Filter
http://www.benzedrine.cx/pf.html

Packet Filter HOWTO
http://www.inebriated.demon.nl/pf-howto/

BackWatcher, Inc.
http://www.backwatcher.com/ 
http://www.backwatcher.org/ 
http://www.backwatcher.net/