Distributed denial of service(DDoS)attacks remain a serious threat on the Internet and again it is very difficult to devise a perfect DDoS defense mechanism.In this paper
we investigate the damage caused by the DDoS attacks and analyze the root reasons why DDoS attacks take place.After that
we make a survey on the new solutions against DDoS attacks especially after year 2005
which mainly includes 1)Network filters based on ISP;2)Proof-of-work;3)Overlay network;and 4)Network capabilities.We analyze the advantages and disadvantages of these solutions
and conclude the features of the deployed solutions.Finally
we discuss possible future defense strategies against the DDoS attacks.