Cloud computing has become popular and a huge platform for computing where large number of data are available online. Nature of cloud computing is distributed, due to this kind of nature they have become easy target for attackers to exploits the security vulnerability. Availability of data is most important part of cloud computing and even for economic growth of the society. Attack name Denial of Service (DoS) is an attempt to make the resource unavailable to its intended user by flooding network with malicious packets. Attacker spoof IP to hide the source of attack, however if the IP (Internet Protocol) address is kept same throughout the attack even it is spoofed DoS Attack can be prevented.