Setting method, network device, and communication system

A network device that forwards frames in a home network, the network device comprising:

• an obtainer that obtains a first certificate of one of a plurality of types from a first device that is attempting to connect to the network device and that holds the first certificate;
• an identifier that identifies a first type as the type of the first certificate obtained by the obtainer;
• and
• a setter that performs first setting processing for connecting the first device to the network device such that the first device belongs to a first segment associated with the first type identified by the identifier among one or more segments that are one or more forwarding ranges of the frames of the network device and that are each associated with a type of certificate.