Bridges Anyone?

[Mike Barton <mike@dad.state.vt.us>]

Hi all! Here's the story... I'd like to setup a dual NIC Debian box to act
as a filtering bridge. The goal is to filter IP traffic in by port and,
hopefully, other protocols. For example, I'd like to ship traffic destined
to two (or more) web servers to their respective hosts untouched. However,
any other IP requests for port 80 would be silently dropped. The traffic
through the bridge would use real IP addresses which makes NAT unsuitable.
Any pointers, hints, greatly appreciated....