Abstract: A transfer device (10) transfers a packet between a first network (31) and a second network connected to a network device (32) via a first communication path and a second communication path, the network device (32) functioning as a gateway for connecting to the first network (31). The transfer device (10) includes a control unit (16, 22). The network device (32) holds correspondence information indicating a correspondence relationship between each of a first communication port for connecting to the first communication path and a second communication port for connecting to the second communication path, and address information regarding a destination of the packet. The control unit (16, 22) transmits, to the network device (32), an update control signal for the network device (32) to update the address information associated with the first communication port in the correspondence information.

Abstract: The disclosure has an object to allow local expansion without causing any loop. The disclosure is a system to which two nodes respectively belonging to different ring networks are connected, wherein the two nodes are connected to each other using a predetermined customized port, upon receipt of a predetermined unicast frame, one of the two nodes transmits the frame to another of the two nodes using the customized port, upon receipt of the predetermined unicast frame from the customized port, the other of the two nodes forwards the unicast frame, and upon receipt of a frame different from the predetermined unicast frame from the customized port, the other of the two nodes discards the frame.

Abstract: An object of the present disclosure is to provide a communication system, a communication path switching method, a communication device, and a program capable of continuing communication or shortening a communication disconnection time even during an operation of switching paths. A communication system according to the present disclosure is a communication system including two communication devices forming a duplex path with a common access network.

Abstract: An object is to provide a route switching method, a transfer device, and communication system that can continue communication even during route switching work. In a route switching method according to the present invention, in bypass transfer that transfers a packet while bypassing a non-transferable route, the transfer device having detected the non-transferable route attaches a bypass packet flag to the packet that passes through a non-transferable route and specifies the packet as a bypass packet, the transfer device having detected the non-transferable route returns the bypass packet and transfers the bypass packet in a direction opposite to that of the packet in the ring network, and the transfer device for which the blocked port is set in the ring network transfers the bypass packet through the blocked port before the route switching work.