This read-only MacAddress, held on the ComPort, holds a MAC address value learned or configured in that STU's Ethernet action table - the actual client/host address, not the STU's own identity. An admin reviews these entries to see exactly which host devices have been seen on a subscriber's LAN segment behind the STU. For example, an unexpected third MAC address showing up as stuEtherMacAddr on a residential STU that should only have two devices would suggest an unauthorized device sharing the connection.