Patent ID: 7804768

Claim:
A method for redundantly linking a WAN node device that forms a WAN and a LAN-communication linking device that forms a LAN, to enable communication between the two, the method comprising: first selecting, using a processor, one of a plurality of WAN-side input-output steps by which packets are exchanged between the WAN and the LAN in the WAN node device, wherein a packet from the LAN to the WAN is received and a packet from the WAN to LAN is sent, by the first selected WAN-side input-output step; storing source terminal identification data of a packet received by the LAN-communication linking device, in association with identification data of a LAN-side input-output step at which the packet is received; second selecting, based on the identification data of the LAN-side input-output step stored by the storing, the LAN-side input-output step from a plurality of LAN-side input-output steps to transmit a packet from the LAN to the WAN node device; monitoring failure in the LAN-side input-output step; and deleting the source terminal identification data stored in association with the LAN-side input-output step when failure is detected at the monitoring.