An advance research on utilization of Mobile Ad-hoc Networks (MANET) has noticed an equal increase in the development of number of attack strategies, detection mechanisms and counter measures. Most of these have been evaluated and analyzed by using separate simulation environments and performance metrics. However, the simulation results were not comparable due to the different evaluation scenarios and implementations like network performance with and without attack detection. Hence in this paper, the impact of attacks on MANET performance is analyzed and evaluated based on the different performance metrics. The major aim of this paper is to analyse the network without the attack on DSR protocol and compared with the network under blackhole and grayhole attack using performance metrics like throughput, Packet Delivery Ratio (PDR), packet drop rate and normalized routing overhead in two different scenarios. The simulation results are carried out by using Network Simulator-2 (NS-2) which shows that the efficiency of network with and without attacks.
