ISA Server and Network Card Config

I am setting up an ISA server and having trouble configuring the NIC cards. WAN card going to router is 10.2.1.3/16 and LOCAL card goes to 10.1.1.2/16 . My inside router address is 10.2.1.1 . What do I have for default gateway and dns for the two cards? How does ISA know which card is which?