This field records the port number reported by the device at the far end of this direct-attached FC storage port's physical link. For one physical FC port on the fabric interconnect that is a member of a direct-attached (non-SAN-switch) external storage connection, comparing local and peer port numbers lets UCS Manager render an accurate topology diagram, and a peer port number that keeps changing between polls can itself be a symptom of a flapping or misbehaving link partner. A stable link here would report the same peer port number, say port 11, on every poll rather than jumping around.