This gauge identifies the local port number associated with the physical Fibre Channel endpoint representing one FC-facing port on the fabric interconnect, together with the neighbor device it discovers on the wire. An administrator cross-referencing SNMP data with a physical rack diagram uses portId on this PhysFcEp instance to know exactly which physical port the reading applies to. For example, an alert referencing this PhysFcEp instance's DN is only actionable once the operator also reads portId to know which physical port to walk over and inspect.