Abstract: A system for rewriting a VLAN-ID in an Ethernet frame containing VLAN-IDs is provided to solve a communications problem that could arise due to the difference between IDs in a plurality of interconnected networks employing different schemes for determining an ID. In a VLAN comprised of a plurality of interconnected Ethernet networks (NX, NY), converters (CONVX, CONVY) for converting a user ID in one of the Ethernet networks to another ID of the same user in another Ethernet network is provided in an interface portion where the plurality of Ethernet networks are connected. The converters make it possible to uniquely identify all the users by their IDs throughout the VLAN.