This carries the Dn of the underlying local endpoint object that this compute cartridge's physical port endpoint actually represents, letting a management tool resolve this row back to the concrete hardware endpoint it describes. Because a cartridge can expose more than one physical port endpoint object internally, this field is how an admin's script disambiguates which specific port on that cartridge a given row of the fabric table is describing. A value like 'sys/chassis-3/slot-2/board/port-1' points at the first physical port on the board of that specific cartridge.