A first relay server connected to a communication terminal via a first LAN and connected to a second relay server via a wide area network, the second relay server being connected to a second LAN, the first relay server comprising: a setting unit configured to activate or deactivate a routing function; a relay group information sharing unit configured to share, with the second relay server, a relay group information including information used to specify the first relay server and the second relay server constituting the relay group; a network address information registration unit configured to register a network address information; a routing session establishment unit configured to, upon receiving an instruction to route a communication packet between the first relay server and the second relay server after the routing function is activated, by the setting unit, transmit a network address information of the first LAN that routes a communication packet via the first relay server to the second relay server, receive a network address information of the second LAN that routes a communication packet via the second relay server from the second relay server, register the network address information of the first LAN and the network address information of the second LAN in the network address information registration unit, and establish a routing session with the second relay server to route the communication packet between the first LAN and the second LAN; a routing processing unit configured to, upon receiving a communication packet from the communication terminal, determine whether or not a network address information corresponding to the destination address of the communication packet has been registered in the network address information registration unit, specify the second relay server as a relay server capable of routing the communication packet to a network address corresponding to the destination address, and transfer the communication packet through the routing session with the second relay server; and a routing session disconnection unit configured to receive an instruction to deactivate the routing session from the setting unit, deactivate the routing session, and delete the network address information from the network address information registration unit. a setting unit configured to activate or deactivate a routing function; a relay group information sharing unit configured to share, with the second relay server, a relay group information including information used to specify the first relay server and the second relay server constituting the relay group; a network address information registration unit configured to register a network address information; a routing session establishment unit configured to, upon receiving an instruction to route a communication packet between the first relay server and the second relay server after the routing function is activated, by the setting unit, transmit a network address information of the first LAN that routes a communication packet via the first relay server to the second relay server, receive a network address information of the second LAN that routes a communication packet via the second relay server from the second relay server, register the network address information of the first LAN and the network address information of the second LAN in the network address information registration unit, and establish a routing session with the second relay server to route the communication packet between the first LAN and the second LAN; a routing processing unit configured to, upon receiving a communication packet from the communication terminal, determine whether or not a network address information corresponding to the destination address of the communication packet has been registered in the network address information registration unit, specify the second relay server as a relay server capable of routing the communication packet to a network address corresponding to the destination address, and transfer the communication packet through the routing session with the second relay server; and a routing session disconnection unit configured to receive an instruction to deactivate the routing session from the setting unit, deactivate the routing session, and delete the network address information from the network address information registration unit.