Untangle 11.0 Install - NIC setup

I have installed Untangle 11.0 on a standalone PC. I have a duel nic card and an on board nic. I have assigned the internal nic to 192.168.0.170 (our internal IP) and the external is set to 192.168.2.1. My confusion lies on what ip to set the external. This will be the connection going from my cisco to the untangle box.

I can provide additional info as need.

Thanks.