Abstract: A network apparatus which is one of two network apparatuses using a tunneling protocol and which accommodates a user, wherein the network apparatus includes a function for uniquely determining an identifier in a header of the tunneling protocol in accordance with a setting made by a network operation administrator, and encapsulating and transmitting a packet with the determined identifier, and the other network apparatuses connected to the DPI apparatus 10 includes a function of carrying out decapsulation processing, converting the identifier in the tunneling protocol header into an identifier associated with the output destination interface, attaching a conversion result to a decapsulated packet as an internal control tag, and transferring the conversion result to hardware carrying out packet transfer processing.