International Journal of Scientific & Engineering Research Volume 2, Issue 8,August-2011 1 ISSN 2229-5518 Performance Analysis of Aodv Protocol under Black Hole Attack Monika Roopak , Dr. Bvr Reddy ABSTRACT- Mobile Ad-hoc networks are a collection of mobile hosts that communicate with each other without any infrastructure. Due to security vulnerabilities of the routing protocols, wireless ad hoc networks may be unprotected against attacks by the malicious nodes. One of these attacks is the Black Hole Attack against network integrity absorbing all data packets in the network. Since the data packets do not reach the destination node on account of this attack, data loss will occur. In this paper are doing simulation study of network under black hole attack and do comparison with the network without attack working on AODV protocol using various performance metrics such as throughput, PDF and End to End delay in three different scenarios. Keywords- Ad hoc network, black hole , AODV, MANET, PDR, RREQ, RREP ȯȯȯȯȯȯȯȯȯȯ  ȯȯȯȯȯȯȯȯȯȯ 1. 1 INTRODUCTION ireless network is the network of mobile computer nodes or stations that are not physically wired. The main advantage of this is communicating with rest of the world while being mobile. The disadvantages are their limited bandwidth, memory, processing capabilities and open medium. Two basic system models are fixed backbone wireless system and Wireless Mobile Ad hoc Network (MANET). An ad hoc network is a collection of nodes that do not rely on a predefined infrastructure to keep the network connected. So the functioning of ad hoc networks is dependent on the trust and co-operation between nodes. Nodes help each other in conveying information about the topology of the network and share the responsibility of managing the network. Hence in addition to acting as hosts, each mobile node does the function of routing and relaying messages for other mobile nodes [1].In these networks, besides acting as a host, each node also acts as a router and forwards packets to the correct node in the network once a route is established. In this paper we will study the ad hoc network with and without the black hole attack using performance metrics PDF, Throughput and End to End delay. 2. AODV The AODV [2,3] routing protocol is a reactive routing protocol therefore, routes are determined only when needed. Figure 1 shows the message exchanges of the AODV protocol. Hello messages may be used to detect and monitor links to neighbors. If Hello messages are used, each active node periodically broadcasts a Hello message that all its neighbors receive. Because nodes periodically send Hello messages, if a node fails to receive several Hello messages from a neighbor, a link break is detected. When a source has data to transmit to an unknown destination, it broadcasts a Route Request (RREQ) for that destination. At each intermediate node, when a RREQ is received a route to the source is created. If the receiving node has not received this RREQ before, is not the destination and does not have a current route to the destination, it rebroadcasts the RREQ. If the receiving node is the destination or has a current route to the destination, it generates a Route Reply (RREP). The RREP is unicast in a hop-by-hop fashion to the source. As the RREP propagates, each intermediate node creates a route to the destination. When the source receives the RREP, it records the route to the destination and can begin sending data. If multiple RREPs are received by the source, the route with the shortest hop count is chosen. As data flow from the source to the destination, each node along the route updates the timers associated with the routes to the source and destination, maintaining the routes in the routing table. If a route is not used for some period of time, a node cannot be sure whether the route is still valid; consequently, the node removes the route from its routing table. If data is flowing and a link break is detected, a Route Error (RERR) is sent to the source of the data in a hop-by- hop fashion. As the RERR propagates towards the source, each intermediate node invalidates routes to any unreachable destinations. When the source of the data receives the RERR, it invalidates the route and reinitiates route discovery if necessary. W