A network relay device includes a communication unit, an authentication processing unit, a DHCP snooping processing unit, and a terminal search processing unit. The authentication processing unit creates first information specifying an authenticated terminal device according to web authentication, and manages whether relay of communication data between a terminal device and a node on the specified network is permissible based on the first information. The DHCP snooping processing unit executes snooping of DHCP communication data between a terminal device and a DHCP server, and creates second information specifying a layer 3 address allocated to each terminal device. The terminal search processing unit specifies an authenticated terminal device based on the first information, specifies a layer 3 address allocated to the specified authenticated terminal device based on the second information, and causes the communication unit to send, to the specified layer 3 address, confirmation communication data.