| 摘要 |
PROBLEM TO BE SOLVED: To provide a DNS server filter which prevents the intrusion of a nonmember of an organization into the network of the organization through the user of network architecture information and prevents the operation of the DNS server from becoming abnormal by receiving a packet of an abnormal system. SOLUTION: The DNS server filter is provided with a packet reception part receiving an inquiry from a terminal and the DNS server in a DNS protocol and a response packet from the DNS server, a session management part which is provided with a session management table for managing an inquiry request, manages inquiry and response packets and controls a whole system, a packet verification part inspecting whether or not the inquiry and response packets are abnormal, a request generation part generating the inquiry packet to the DNS server, a response generation part generating the response packet returned to the transmission source of the inquiry packet and a packet transmission part transmitting the inquiry and response packets. It is inspected whether abnormality occurs in a content before the received DNS packet is transferred to the DNS server and an error response packet is generated when abnormality is detected so as to return it to the request source.
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