Abstract

A table memory stores an address transformation table (AT table) which contains no address pairs therein before initialization of the system. A hash function memory stores a plurality of hash functions which are selectively used in correspondence with the sizes of a backbone network (BN) and a local area network (LAN), when an address pair consisting of a node address and a LAN address, of a LAN to which a node indicated by the node address belongs, is registered in the AT table. When a control unit receives frame data from the LAN or the BN, it automatically generates the above address pair consisting of the node address and the LAN address in the AT table by selecting one of the plurality of hash functions. During registration, if the AT table reaches the limit of its available storage space, and a new address is to be registered, the control unit then generates an AT table larger in size than the current AT table, using another hash function, and registers the already registered address pairs and the new address pair in the newly enlarged AT table.