Bridging and port mirroring

[Brian McCann]

I've poked around on the web, but come up empty.  And I find it hard
to believe there's not a simple way to do this, if it hasn't been done
before.

I've got a server with two nics configured for bridging and running
bunches of ipfw rules.  I'd like to add a 3rd NIC and have it mirror
the 2nd NIC (so all traffic into and out of nic2 goes to nic3), so I
can run an IDS on another server.  Yes, I know that has the potential
to overload nic3 if there is a lot of traffic going in and out of
nic2, but that's not an issue for me.

Has anyone done this before, or know how to do this?

Thanks,
--Brian