Abstract-MANET is autonomous, decentralized, infrastructure less, cooperative & self-configurable network. It composed of continuously moving mobile nodes which deploy dynamic topologies. The mobile nodes in MANET can act as host as well as router. There are various protocols available for managing these mobile nodes which are formally categorized in proactive & reactive and hybrid protocols. As the network employs dynamic topology and no infrastructure, it is prone to so many security attacks viz. flooding, DoS, wormhole, grey hole, black hole, eavesdropping, jamming, man-in-the-middle, Sybil attacks etc. Among them black hole attack is most popular attack in which the attacker behave as black node and fool the source node that it has the shortest path available to the destination and thus prevents the packet reaching the destination. In this paper a new technique is proposed to detect and isolate black hole attack using fake route request packets. The simulation results show that the scheme is better than the previously described schemes in the terms of packet delay and throughput.