This read-write value identifies the interface to which this SMDS address is assigned, i.e., the physical or logical port on the switch that this address's traffic enters or exits through. This ties an otherwise abstract address entry to a concrete piece of hardware, which is necessary for the switch to know where to deliver traffic destined for this address. An engineer moving a customer's SMDS service to a different port after a hardware upgrade would update smdsaddrIf to point at the new port's interface index.