1. A network-based communication system, comprising: at least one server containing a processor for connecting a plurality of processing modules including: a processing module embodied in hardware for obtaining a corresponding dynamic address by sending an identifier to a mapping notification system which stores a pair of an identifier and a dynamic address; and at least one additional processing module embodied in hardware for determining whether or not a dynamic address stored in the mapping notification system is correct by accessing other communication node to which the dynamic address obtained by the processing module is assigned, wherein when the determining means determines that the address is not correct, (i) said obtaining process and determination process are executed again, (ii) an execution of a process to be executed after said determination process is stopped, or (iii) a control process for preventing from sending back a reply of said address from the mapping notification system is executed.