This value is the index number that uniquely identifies one entry in the device's IPX traffic filtering/forwarding table, tying together a source address, destination address, and the filtering action to apply between them. An admin assigns this when creating a new IPX filter rule, and it becomes the key used to reference that specific rule's settings afterward. For example, creating a rule with index 5 lets the admin later reference that specific source/destination/action combination distinctly from other filter rules in the table.