An Ad hoc network in a wireless system consist of an autonomous system, without centralization which results forming of mobile nodes. In MANET, each node works in a dual form that consists of a router as well as hosts. These nodes configure dynamically and communicate using hop to hop. Due to its simplicity it is used in mobile conferencing, military communication.
In MANET nodes can join and leave the network so MANET becomes vulnerable. Certain factors like dynamic network configures, distribution cooperation, open medium terrorized in routing which give rise to security issues. Once such protocol AODV has been a victim of security. In existing, MANET faces a severe problem known as the Black Hole problem. This Black hole problem is mostly found in reactive routing protocol called AODV.The black hole conducts its Malicious node during route discovery process. Black hole node is a severe threat in AODV protocol that easily employed and becomes vulnerable in MANET. In this paper various techniques are discussed to overcome the Black hole attack