Frame-transfer control device, DoS-attack preventing device, and DoS-attack preventing system

摘要

A prior information collecting unit transmits in advance a SYN/ACK frame to an address of a client in an external network, and monitors a response to the SYN/ACK frame. If there is no response, the prior information collecting unit determines that the address is a valid attack address. If there is a response with a RST frame, the prior information collecting unit determines that the address is an invalid attack address. An address holding unit stores a responding state of the client. A valid attack identifying unit detects a valid attack frame having a valid attack address as a source address from among frames addressed to the server, based on information stored in the address holding unit. A flow rate limiting unit limits a flow rate at the time of transferring the valid attack frames to the server.