To first relate information for authenticating a user who is a packet transmitter, to a network where a user IP packet passes, and to further use this information for user authentication and service authentication in the network in a domain name resolution/authentication method and apparatus for providing the information to the network whereon the IP packet is relayed.

A notification 801 indicating an FQDN that a present device 100 manages, and an IP address of the present device 100 is sent to a neighboring DNS server, the FQDN indicated in the received notification 801 and an IP address of the neighboring DNS server 100 are correspondingly registered in an FQDN database 81, and the notification 801 is transferred to the next neighboring DNS server. An authenticated transmission source IP address 83a is registered in advance, a domain name resolution request 802 is transferred through a path that is determined on the basis of the FQDN database 81, and when a transmission source IP address contained in the request 802 is not authenticated, the request 802 is discarded.

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