Architectural implementation
One Nic is to be connected with external network and the other is connected to the internal network, which will actually provide an additional layer of protection. So with these NICs, all the traffic must go through the firewall in order to move between internal and external networks. So the implementation of this kind of architecture will often make use of Nat. So normally Nat is a method of mapping which is assigned IP addresses to special ranges of no Routable internal IP addresses