An extranet direct route allowing extranet forwarding to a directly linked device is written in a layer 2-layer 3-integrated forwarding table. The procedure of introducing a layer 3 address-to-layer 2 address correspondence relation table entry into the layer 2-layer 3-integrated forwarding table searches the layer 2-layer 3-integrated forwarding table with a layer 3 address of the correspondence relation table entry and a layer 3 interface as search keys to retrieve any forwarding entry relating to an extranet direct route as a forwarding destination. The procedure subsequently extracts a VRF of each retrieved forwarding entry and introduces the correspondence relation table entry for the extracted VRF into the layer 2-layer 3-integrated forwarding table.