Patent ID: 8854949

Claim:
A network relay device configured to relay data in a layer 2 network, comprising: first and second communication ports configured to belong to the layer 2 network; a snooping module configured to generate snooping information, based on snooping with respect to a multicast joining message for notifying of joining to a multicast group, wherein the snooping information correlates the first communication port set to a multicast transfer port, from which a multicast frame is to be transferred, to a destination MAC address of the multicast frame; a transfer information storage unit configured to store the snooping information; a multicast sending module configured to refer to the snooping information stored in the transfer information storage unit and send a multicast frame received from the layer 2 network, from the correlated multicast transfer port; a failure detector configured to detect a communication failure in the layer 2 network; and a port adding module configured to, in response to detection of the communication failure by the failure detector, additionally set the second communication port, in addition to the first communication port, to the multicast transfer port, so as to update the snooping information stored in the transfer information storage unit.