Tackling Application-layer DDoS Attacks

In application-layer distributed denial of service (DDoS) attacks, zombie machines attack the victim server through legitimate packets such that packets havelegitimate format and are sent through normal TCP connections. Consequently, neither intrusion detection systems (IDS) nor victim server can detects malicious packets. This paper proposes a novel scheme which is called ConnectionScore to resist against such DDoS attacks. During the attack time, anyconnection is scored based on history and statistical analysis which has been done during the normal condition. The bottleneck resources are retaken from those connections which take lower scores. Our analysis shows that connections established by the adversary give low scores. In fact, ConnectionScore technique can estimate legitimacy of connections with high probability.Toevaluate performanceofthe scheme,weperformexperimentson Emulabenvironmentusingreal traceroute data of ClarkNet WWW server.