This read-only INTEGER is the index key for a specific entry in the IPX station fast-forwarding table. It's the identifier an admin's SNMP tooling uses to walk through and correlate the various per-station IPX forwarding fields (destination network, node, MAC addresses) that belong to the same station entry. For example, when auditing which stations have IPX routes installed, this index is what ties together a given station's full set of forwarding attributes.