Peter N. M. Hansteen, The Book of PF, 2nd Edition, No Starch Press November 2010, also The Book of PF (1st Ed), No Starch Press December 2007
My online PF tutorial, several formats http://home.nuug.no/~peter/pf/.
Slides for this talk at http://home.nuug.no/~peter/pf/eurobsdcon2012/
OpenBSDs web http://www.openbsd.org/
OpenBSDs FAQ, http://www.openbsd.org/faq/index.html
PF User Guide http://www.openbsd.org/faq/pf/index.html
Daniel Hartmeier's PF pages, http://www.benzedrine.cx/pf.html
Daniel Hartmeier: Design and Performance of the OpenBSD Stateful Packet Filter (pf), http://www.benzedrine.cx/pf-paper.html (presented at Usenix 2002)
Randal L. Schwartz: Monitoring Net Traffic with OpenBSD's Packet Filter, http://www.stonehenge.com/merlyn/UnixReview/col51.html
Unix.se: Brandvägg med OpenBSD, http://unix.se/Brandv%E4gg_med_OpenBSD
Randal L. Schwartz: Blog for Thu, Jan 29, 2004, http://use.perl.org/~merlyn/journal/17094
RFC 1631, "The IP Network Address Translator (NAT)", May 1994 http://www.ietf.org/rfc/rfc1631.txt?number=1631
RFC 1918, "Address Allocation for Private Internets", February 1996 http://www.ietf.org/rfc/rfc1918.txt?number=1918
The FreeBSD PF home page, http://pf4freebsd.love2party.net/
Marcus Ranum: The Six Dumbest Ideas in Computer Security, September 1, 2005
Kjell Jørgen Hole WiFi courseware, http://www.kjhole.com/Standards/WiFi/WiFiDownloads.html, also see wifinetnews.com; also The Unofficial 802.11 Security Web Page comes higly recommended.
Greylisting.org greylisting.org
Evan Harris: The Next Step in the Spam Control War: Greylisting (the original greylisting paper)
Mark Uemura: What's New in 4.3: authpf-noip
Henning Brauer: Carp and STP meet switch security
Henning Brauer: 10 years of pf
Henning Brauer: Puffy At Work: Code Right And Secure, The OpenBSD Way
Michael W. Lucas: Network Flow Analysis, No Starch Press 2010