This read-only integer identifies which interface a given row of the ClearTrac7 IP address table's address is bound to; the source description is empty, so this is inferred from the field name pairing an address with an interface reference. An administrator uses it to map a specific configured IP address back to the physical or logical interface carrying it. For example, cross-referencing this value against the intfIndex table lets the admin determine exactly which port a particular address in ipaddrAddr is assigned to.