Relay system and switching device

A relay system comprising:

• a first switching device and a second switching device each having a first port group made up of one or a plurality of first ports, a second port and a bridge port, the first switching device and the second switching device being connected to each other by a communication line via the bridge ports;
• and
• a third switching device connected to the one or the plurality of first ports of the first switching device and the one or the plurality of first ports of the second switching device via different communication lines, the third switching device setting a link aggregation group on ports serving as connection sources of the communication lines,
• wherein each of the first switching device and the second switching device includes:
• a MCLAG table which retains the one or the plurality of first ports in association with a first identifier;
• a port control unit which controls the first port group to a first state in which transmission and reception are both permitted when no fault is present and the first port group is set to active and controls the first port group to a second state in which transmission and reception are both prohibited when no fault is present and the first port group is set to standby;
• a relay processing unit which relays a frame containing the first identifier as a destination port to the first port group when the first port group is controlled to the first state and relays a frame containing the first identifier as a destination port to the bridge port when the first port group is controlled to the second state;
• and
• a transmission stop instructing unit which instructs the third switching device to stop frame transmission to the first port group when the first port group is controlled to the second state, and
• the first port group of the first switching device is set to the active and the first port group of the second switching device is set to the standby.