Outernet DNS searching units are included in a host, a DNS server, a router where a DNS server is registered, and a router where a DNS server is not registered, allowing Internet-enabled terminals to automatically search for a DNS server in an outernet. The host creates a DNS search message and transmits it to a subnet to which the host belongs so as to receive a response message. If no response message is received from the subnet (i.e., a DNS server is not connected to the subnet), the DNS search message is transmitted to an outernet to which the host does not belong, to which a DNS server is connected. Further, when a DNS server does not respond to a DNS search message from a host, a hop limit is increased to resend the DNS search message, thereby preventing waste of network bandwidth and easily detecting the closest DNS server.