World is changing very fast and technology is not behind. Everyday something new is created and deployed, and all of this is done over the Internet. In this era, organizations want more work to be done with least price possible and are ready to use information for competitive advantage. Furthermore, other important factors like globalization, aging data centre, storage growth, application explosion, cost of ownership and acquisition has lead organization to move towards cloud computing. Cloud computing is basically the collection of services hosted over the Internet in the virtual environment. Therefore, user can use resources according to their demand and only pay for them, as the demand increases or decreases these resources can be increased or released accordingly. As popularity of cloud is increasing so are the threats related to it. One such attack which is performed on cloud i.e. the DDoS attack is addressed in detail in this paper. DDoS attack or Distributed Denial of service attack [2, 20] is one of the most common attacks nowadays, as it is very easy to carry out using some simple scripts or tools which are freely available online. In DDoS attack an attacker creates some zombie machines or bots by infecting machines over the Internet. Then these compromised machines are used to perform attack on victim. When traffic from so many machines are directed toward a single victim, victim’s resources like bandwidth, CPU, memory etc starts getting exhausted and its services are no longer available to serve requests from legitimate users. This whole network of bots is called botnet, in botnets the bots may be controlled centrally by a C&C server or P2P. The commands are sent to bot systems directly by attackers or handlers which are again compromised machines over the Internet. This paper mainly discusses the DDoS attack on cloud environment. When DDoS attack occurs in cloud environment, it exhausts all the resources of the VM and overburdens the system; cloud can handle this situation by allocating more resources to this VM to accumulate all the requests made to it. This allocation of more resources can go on to an extent where either cloud provider runs out of resources to allocate or the owner of VM cannot pay for usage of these resources anymore. Furthermore, to deal with this issue limit may be imposed on connection time or bandwidth but this would just make the idea of cloud computing disappear. Hence, a better approach is required to prevent cloud environment from this attack. Therefore, fog computing can be used to provides protection. Fog computing [3] also referred as “edge computing” is a decentralized computing infrastructure where edge devices like routers, switches etc provides storage, computation, control, communication, management and measurement. It places some of the transactions and resources at the edge to reduce the need of going to cloud. Fog reduces the need for bandwidth by using distributed strategy which results in lower cost and improved efficiency.