Patent ID: 7680949

Claim:
A source address selection system comprising: a router device connectable to a plurality of Internet service providers, and a communication node connected to the router device, wherein: the router device includes: a storage unit configured to store management information on connectivities with the Internet service providers; a first checking unit configured to periodically check connectivities of each of the Internet service providers and update the management information according to a result of the check; a first receiving unit configured to receive a network prefix provided by an Internet service provider for which a connectivity is confirmed by the first checking unit and store the network prefix into the storage unit as a piece of the management information; and a notification unit configured to notify the communication node of the network prefix received by the first receiving unit; the communication node includes: a second receiving unit configured to receive the network prefix from the router device; a generation unit configured to generate a network address according to the network prefix and an identifier unique to the communication node; and a transmission unit configured to transmit a packet by attaching the network address as a source address to a header; and the router device further includes: a second checking unit configured to search the management information stored in the storage unit for whether or not the packet received from the communication node has the source address of the network prefix received from the Internet service provider indicating that the Internet service provider's connectivity has been currently confirmed; and a control unit configured to control a transferring of the packet from the communication node to the Internet service provider, wherein, when it is determined by the second checking unit that the source address includes a network prefix, provided by the Internet service provider and for which the connectivity has been confirmed, the control unit permits the router to transfer the packet to the Internet service provider based on the determination that the source address includes the network prefix, and wherein, when it is determined by the second checking unit that the source address includes a different network prefix from the network prefix, provided by the Internet service provider and for which the connectivity has been confirmed, the control unit does not permit the router to transfer the packet to the Internet service provider but does permit the router to notify the communication node that the transferring of the packet was not carried out based on the determination that the source address includes the different network prefix.