One of the key issues of Adhoc network is that it is more prone to security threats due to insecure boundaries, threats from compromised nodes, lack of central monitoring system, restricted power supply, continuously changing topology, open medium and cooperative algorithms. MANETS are vulnerable to different types of DoS attack. Black hole attack is a network layer which uses destination sequence number to claim that it has a fresh and shortest path to the destination and consumes all the

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... ts forwarded by the source node 1,2 . The aim of this paper is to study the impact of the black hole attack in the performance parameters of wireless ad hoc networks with AODV routing protocol for different scenarios like varying network traffic, network size, black hole nodes, mobility and position of attackers. The rest of the paper is organized as follows. Section 2 provides an overview of security attacks in MANET Section 3 describes overview of AODV protocol Section 4 describes how the black hole attack is performed on AODV, Section 5 deals with performance parameters affected due to black hole attack, Section 6 presents the simulation scenarios and comparison of results and finally Section 7 discusses the conclusion with the plan for the future work. Abstract Background/Objectives: Mobile Adhoc Networks (MANETS) are prone to different types of attacks due to lack of central monitoring facility. The objective is to investigate the effect of black hole attack on the network layer of MANET for different network scenarios. Method: A black hole attack is a network layer attack which utilizes the destination sequence number to claim that it has a fresh and a shortest path to the destination and consumes all the packets forwarded by the source. The various network scenarios of MANETS with AODV routing protocol are simulated using Network Simulator Version 2 (NS-2) to analyse the performance with and without the black hole attack. The scenarios are created by varying the number of nodes and nodes speed, varying position and number of the black hole nodes and number of flows. The performance parameters like PDR, delay, throughput, packet drop and control overhead are measured. Findings: The black hole attack degrades the network performance. The impact of attack is severe when the attacker is near to the source node, less severe when it is in midway between source and destination and has least effect when it is farther from the source. The overall throughput and PDR increases with the number of flows but reduces with the attack. With the increase in the black hole attackers, the PDR and throughput reduces and close to zero as the number of black hole nodes are maximum. The packet drop also increases with the attack. The overall delay factor varies based on the position of the attackers. Throughput, PDR and control overhead decreases with the network size due to congestion and average delay reduces with black hole attack as the black node sends the Route ERRor (RREP) without performing any route checking. As the mobility varies, the delay and packet drop increases but PDR and throughput decreases as the nodes moves randomly in all directions. Conclusion: The simulation results gives a very good comparison of performance of MANETS with and with out black hole attack for different network scenarios.