Communication system, communication method, network device and program

A communication method executed by a communication system in which a first network and a second network are connected to each other by a plurality of network apparatuses, the method comprising:

• disabling, by only a specific path of a plurality of paths, a transfer prevention unit that prevents transfer of a broadcast frame, an unknown unicast frame, and a multicast frame from the second network to the first network, the transfer prevention unit being included in the plurality of paths;
• transferring a broadcast frame, an unknown unicast frame, and a multicast frame from the second network to the first network by only a specific path of the plurality of paths;
• and
• preventing transfer of the broadcast frame, the unknown unicast frame, and the multicast frame while permitting transfer of known unicast frames on the paths other than the specific path in the plurality of paths by setting a buffer length for temporarily storing frames to zero.

A network apparatus connected to a boundary between a first network and a second network, the network apparatus comprising:

• a transfer prevention unit, including one or more processors, configured to prevent transfer of a broadcast frame, an unknown unicast frame, and a multicast frame from the second network to the first network while permitting transfer of known unicast frames from the second network to the first network;
• a BUM passing/non-passing determination unit, including one or more processors, configured to acquire identification information of a network apparatus provided at a boundary between the first network and the second network via the first network, and determine enabling of the transfer prevention unit by using the acquired information;
• and
• a transfer prevention enabling unit, including one or more processors, configured to enable the transfer prevention unit according to the determination by the BUM passing/non-passing determination unit,
• wherein the transfer prevention unit is configured to prevent transfer of the broadcast frame, the unknown unicast frame, and the multicast frame by setting a buffer length for temporarily storing frames to zero.