Abstract: Cloud consists of distributed data centres located at various geographical locations. Distributed denial of service (DDOS) attack is a major trouble to its availability. DDOS is performed in order to disrupt the services provided by the data centres. The attacker can greatly degrade the quality or fully breakdown victimís network connectivity. The attacker first compromises many agents or hosts and then uses these depletes the target network by using these agents. The main aim of a DDoS attack is to make the victim unable to use the resources. In this paper,a flooding based defence algorithm for DDOS attack is proposed which yields better performance.

Keywords: DDOS, flooding attack, cloud VMM.