IP Filter is a great little firewall package. It does just about everything other free firewalls (ipfwadm, ipchains, ipfw) do, but it's also portable and does neat stuff the others don't. This document is intended to make some cohesive sense of the sparse documentation presently available for ipfilter. Some prior familiarity with packet filtering will be useful, however too much familiarity may make this document a waste of your time. For greater understanding of firewalls, the authors reccomend reading Building Internet Firewalls, Chapman & Zwicky, O'Reilly and Associates; and TCP/IP Illustrated, Volume 1, Stevens, Addison-Wesley.