Mobile Ad-Hoc Networks (MANET) are group of mobile adhoc nodes which could correspond with one to another by using multihop links which are wireless. MANETs are very frequently deployed in various those environments, where there is no centralized management and fixed infrastructure. Here have developed a prevention scheme against the jellyfish attack in MANET environment. Simulation is done in NS2. Here the performance is evaluated on the basis of number of attacker nodes identify in the network along with number of infected packets injected in the network by the attacker nodes to degrade the performance of the network along with the routing overhead of the network.