The invention relates to an indirect distributed
denial of service attack defense method and an indirect distributed
denial of service attack defense
system based on a Web agency. A behavior characteristic of a proxy-to-
server network flow is described by extracting the space-time local property of the proxy-to-
server network flow; the interference of a small-probability large value on an available
signal is restrained by a nonlinear mapping function; a normal behavior model of the proxy-to-
server network is constructed through a hidden semi-markov model (HsMM); normal degree
estimation, namely long-time behavior
estimation and short-time behavior
estimation, under different time scales is performed by using behavior indexes acquired by the model; as to an abnormal behavior sequence (HTTP request sequence), an
attack response is implemented by adopting a soft control method; and the basis of the soft control represents an HsMM
model parameter and a structure index which are used for performing a normal behavior. The parameter for describing the proxy-to-server network is the space-time local property which is irrelevant to the change of the
Web content on a target server; and the detection property of the method is the nature property based on the agent network flow and irrelevant to the size of the
attack flow. By the method, the
attack response can be realized before the resources of the target server are used by the attack flow, so that
early detection can be realized effectively.