How to configure FreeBSD machine as a bridged router?

[Jake Conk]

Hello,

I have 2 nic cards in my machine and I want to place this machine  
between my internet connection and my router without it looking like  
another router between the 2 networks (internet  and my network). I  
want to connect the internet line in the first nic card and the line  
to my network in the second nic card as if it were a 1 port router in  
bridge mode that has 1 line with the internet and the second line that  
goes to my network. Is a setup like this possible with FreeBSD?

The reason why I'm asking is because I want to configure this machine  
with the net.inet.tcp.inflight options and see if it boosts up data  
transfer speeds without changing my network configuration, just adding  
this device in front of it.

Thanks,
- Jake