A relay server mainly includes a VPN group information storage unit, an address filter information storage unit, and a communication control unit. The VPN group information storage unit is arranged and programmed to store information concerning routing apparatuses that define a VPN group and a routing session. The address filter information storage unit is arranged and programmed to store address filter information in association with identification information of the routing apparatus. The communication control unit is arranged and programmed to perform controls of: upon detection of that an address included in the address filter information overlaps, causing a translated address to be associated with the overlapping address, and transmitting the translated address to another routing apparatus; and performing routing based on the address filter information and the translated address.