Data communication system, cache DNS device and communication attack prevention method

摘要

PROBLEM TO BE SOLVED: To solve problems of delay of cyclic investigation caused by ASP, non-linked malicious Web server being latent, flexible communication control being disabled, outflow of communication privacy of a client to ASP and a load of the client.SOLUTION: The present invention relates to a data communication system comprising a cache DNS server 15 and an authority DNS server 23. When a DNS query is received from a client 12, the cache DNS server receives a DNS response including an IP address corresponding to a URL and a safety evaluation result from the authority DNS server 23. In a case where the received safety evaluation result meets a communication permission policy, the cache DNS server permits a transmission to the IP address described on the DNS response for the client 12. The authority DNS server holds the safety evaluation result of each URL connected within an ISP network 92 and, when the DNS query is received, transmits the DNS response to the cache DNS server 15.SELECTED DRAWING: Figure 4