A survey of defense mechanisms against application layer distributed denial of service attacks

Application layer Distributed Denial of Service (DDoS) attacks, which are legitimate in packets and protocols, gradually become a pressing problem to the current network. How to effectively resist this type of attack is becoming even more challenging with the vast resources and techniques increasingly available to attackers. This paper studies the existing application layer DDoS attacks and provides a comprehensive survey of contemporary defense mechanisms. Our primary intention is to comprehensively understand application layer DDoS and the techniques proposed recently to resist it. And we anticipate that the research community could develop better defense mechanisms to counter this type of attack in the near future.