The Drawbridge firewall is part of a security package that was developed
at Texas A&M University and was designed with a large academic
environment in mind.  It is a copyrighted, but freely distributable,
bridging IP packet filter with a powerful filter language and very good
performance.  It's greatest strength is the ability to perform high
speed packet filtering for a large number of individual hosts within an
intranetwork.  It uses a constant-time table lookup algorithm so it can
provide the same level of packet throughput regardless of the number of
filters defined.
