This field records the local physical port number that this direct-attached FC storage port maps to on its fabric interconnect or fabric extender. For one physical FC port on the fabric interconnect that is a member of a direct-attached (non-SAN-switch) external storage connection, this port number is the piece of information an on-site technician actually needs to find the right physical port on the chassis, since the DN alone is not something you can read off a faceplate. For instance this instance might report port 18, meaning it corresponds to the physical port labeled 18 on that switch's faceplate.