Current face implementation requires every face to be assigned with a unique local IP address. That was used to identify the incoming face for data packets although it implies that routers will have multiple ip addresses assign to an interface (strong constraint).

New design will identify the incoming face on data from the PIT entry. The face-input-node for the data forwarding path could possibly identify a list of possible incoming face for the data packet. The datafwd-node will check if the interest outgoing face in the PIT is in the list of the possible incoming face for the data. If no the data is dropped, otherwise accepted.