This gauge reports the port identifier of the neighboring device that the physical Ethernet endpoint representing one Ethernet-facing port on the fabric interconnect, together with the neighbor device it discovers on the wire discovered on the far end of the link. An administrator verifying a cabling diagram compares peerPortId on this PhysEtherEp instance against the port number they expect the far end to be using. For example, a peerPortId that shifts unexpectedly between polls could indicate the far-end device rebooted or its port mapping changed.