This read-write object identifies, via a standard ifIndex value, the interface on which a given network-address-to-media-address equivalence entry is effective, analogous to an ARP table entry but for the CLNS network layer. An admin reviewing address-to-media mappings uses this to know exactly which interface a given NSAP-to-hardware-address binding applies to, important on a device with multiple interfaces on the same CLNS network. For example, if two interfaces both connect to CLNS-capable segments, this field tells the admin which specific interface's mapping table a particular NSAP-to-media-address entry belongs to.