FreeBSD Network Tap
From NSMWiki
Here's the quick how-to for FreeBSD Network Tap setup, as usual 3 network interfaces are needed -
rl0 + rl1 = bridge0
vr0 = mirrored port
To create bridge pseudo interface
# ifconfig bridge0 create
Adding rl0 and rl1 to bridge0 members
# ifconfig bridge0 addm rl0 addm rl1 up
Mirror network traffics that received by bridge0 to vr0
# ifconfig bridge0 span vr0
That's pretty basic for the setup, never forget to tune your sysctl to allow ip forwarding and you are done.

