cmProxyArpPII is a read-only Permanent Interface Identifier identifying the DSL port a given proxy ARP table entry applies to, and it also serves as the index into that table. An administrator uses it to locate the proxy ARP configuration entry for a specific subscriber's DSL port. For example, to check whether proxy ARP is active on a particular customer's line, the operator would look up the table entry matching that line's cmProxyArpPII.