Abstract: MANET (Mobile Ad-hoc Network) is a dynamically changing network which is self-configuring and used in infrastructure less environment. The nodes in MANET act as router and due to its dynamically changing topology it is more open to attacks that causes network issues and service failures. The malicious node(s) causes dropping of packets are black hole and nodes which are dropping and forwarding only selective packets are called as gray hole which is very difficult to detect as other reasons such as congestion and low bandwidth are also responsible for dropping of packets. So, the security solution must be developed to detect and manage black and gray hole attack. In this paper we attempted to mitigate the black hole and gray hole attack and how these attacks are managed.Mobile Ad-hoc Network (MANET), Cluster, Gray hole attack, AODV.