Patent ID: 7649887

Claim:
A bridging device comprising: a storage unit configured to store router identifying information and network prefix information in association with respective lifetimes; a first receiving unit configured to receive a first router advertisement packet containing router identifying information and network prefix information, and the respective lifetimes; an updating unit configured to update the router identifying information, the network prefix information, and the respective lifetimes which are stored in the storage unit by using the router identifying information, the network prefix information, and the respective lifetimes contained in the first router advertisement packet received by the first receiving unit; a determination unit configured to determine whether the router identifying information and the network prefix information stored in the storage unit is valid with respect to the lifetimes stored in the storage unit; a generation unit configured to generate a second router advertisement packet when the determination unit determines that, among the router identifying information stored in the storage unit, identifying information of a router having the highest priority for communication is invalid or when the determination unit determines that any of the network prefix information stored in the storage unit is invalid, the second router advertisement packet containing identifying information of the router having the highest priority of a valid-router identifying information stored in the storage unit and valid-network-prefix information stored in the storage unit, whose lifetimes are set infinite; and a transmission unit configured to transmit the second router advertisement packet to a communication terminal.