A technique is disclosed, by which it is possible to identify a communication node having special function under the condition that a certain communication node knows only the address of a communication node having no special function. According to this technique, a first communication node 10 having a first function (e.g. the mounting of IPv6 and ICMPv6) and a second function (e.g. the mounting of NSIS) transmits a search packet by an echo request packet of ICMPv6 with the purpose of searching a communication node having the first function and the second function to a second communication node 20 having only the first function. The second communication node sends back a response packet to this by an echo response packet of ICMPv6. A communication node 15 having the first function and the second function and being the first receiver of this response packet grasps that own communication node is the search object of the first communication node. Also, by the search packet, desired information can be offered from the first communication node to the communication node of the search object.