DENIAL-OF-SERVICE ATTACK PROTECTING METHOD, DENIAL-OF-SERVICE ATTACK PROTECTING SYSTEM, DENIAL-OF-SERVICE ATTACK PROTECTING DEVICE, REPEATER, DENIAL-OF-SERVICE ATTACK PROTECTING PROGRAM, AND PROGRAM FOR REPEATER

摘要

A gate device (8) acquires normal address information indicating the transmission source of a non-attack packet transmitted by an authorized device (address issuing server (10)) resident on a network (2). According to the normal address information acquired, the gate device (8) generates normal condition information indicating a condition of the non-attack packet. Among the packets received from the network, a packet matched with the condition indicated in the normal condition information is passed while passing of a packet attacking a communication device (7) is limited.