Defense Strategy Using Trust Based Model to Mitigate Active Attacks in DSR Based MANET N. Bhalaji 1 , Dr. A. Shanmugam 2 1 Research Scholar, Anna University of Technology, Coimbatore (Bhalaji.80@gmail.com) 2 Principal, Bannari Amman Institute of Technology Abstract—An ad hoc network is a collection of wireless mobile nodes that forms a temporary network without any centralized administration. While early research effort assumed a friendly and cooperative environment and focused on problems such as wireless channel access and multihop routing, security has become a primary concern in order to provide protected communication between nodes in a potentially hostile environment. Research in wireless indicates that the wireless MANET presents a larger security problem than conventional wired and wireless networks. This paper analyses the black hole and cooperative black hole attack which is one of the new and possible attack in adhoc networks. A black hole is a type of attack that can be easily employed against routing in mobile adhoc networks. In this attack a malicious node advertises itself as having the shortest path to the node whose packets it wants to intercept. To reduce the probability it is proposed to wait and check the replies from all the neighboring nodes to find a safe route. If these malicious nodes work together as a group then the damage will be very serious. This type of attack is called cooperative black hole attack. Our solution discovers the secure route between source and destination by identifying and isolating black hole nodes. In this paper, via simulation, we evaluate the proposed solution and compare it with standard DSR protocol in terms of throughput, Packet delivery ratio and latency. We have conducted extensive experiments using the network simulator-2 to validate our research. Index terms—Trust based routing, secured routing, blackhole attack, Cooperative blackhole attack, adhoc networks, DSR protocol I. INTRODUCTION MANET is multihop infrastructure less network which is characterized by dynamic topology due to node mobility, limited channel bandwidth and limited battery power of nodes. Since mobile nodes in Mobile ad hoc network can move arbitrarily the topology may change frequently at unpredictable times. Transmission and reception parameters may Also impact the topology. The routing algorithm must react quickly to topological changes as per the degree of trust of a node or a complete path between a source and a destination pair. Nodes in Mobile ad hoc network communicate over wireless links. Therefore efficient calculation of trust is a major issue in mobile ad hoc networks because an ad hoc network depends on cooperative and trusting nature of its nodes. As the nodes are dynamic the number of nodes in route selection is always changing thus the degree of trust also keep changing. Survival of ad hoc networks depends on cooperative and trusting nature of its nodes. Black hole Attack: A black hole attack [1] is a kind of denial of service attack where a malicious node can attract all packets by falsely claiming a fresh route to the destination and absorb them without forwarding them to the destination. Cooperative Black hole attack: It is a type of attack in which blackhole nodes act in a group [2] [3]. For example when multiple black hole nodes are acting in coordination with each other, the first black hole node B1 refers to the one of its team mates B2 in the next hop, as depicted in fig. 1. Fig.1.Attack scenario II. RELATED WORK Ramaswamy et al. [3] proposed a solution to defending against the cooperative black hole attacks. But no simulations or performance evaluations have been done. Ramaswamy et al. studied multiple black hole attacks on mobile ad hoc networks. However, they only considered multiple black holes, in which there is no collaboration between these black hole nodes. In this paper, we evaluate the performance of the proposed scheme in defending against the collaborative black hole attack. In DPRAODV [4], they have designed a novel method to detect black hole attack: DPRAODV, which isolates that malicious node from the network. The agent stores the Destination sequence number of incoming 92 JOURNAL OF ADVANCES IN INFORMATION TECHNOLOGY, VOL. 2, NO. 2, MAY 2011 © 2011 ACADEMY PUBLISHER doi:10.4304/jait.2.2.92-98