Protecting the network layer from malicious attacks is an important and challenging security issue in mobile ad hoc networks (MANETs). In this paper, a security mechanism is proposed to defend against a cooperative gray hole attack on the well known AODV routing protocol in MANETs. A gray hole is a node that selectively drops and forwards data packets after it advertises itself as having the shortest path to the destination node in response to a route request message from a source node. The proposed mechanism does not apply any cryptographic primitives on the routing messages. Instead, it protects the network by detecting and reacting to malicious activities of any node. Simulation results show that the scheme has a significantly high detection rate with moderate network traffic overhead.
A Mobile Ad Hoc Network (MANET) is a group of mobile nodes that cooperate and forward packets for each other. Such networks extend the limited wireless transmission range of each node by multi-hop packet forwarding, and thus they are ideally suited for scenarios in which pre-deployed infrastructure support is not available. MANETs have some special characteristic features such as unreliable wireless links used for communication between hosts, constantly changing network topologies, limited bandwidth, battery power, low computation power etc. While these characteristics are essential for the flexibility of MANETs, they introduce specific security concerns that are either absent or less severe in wired networks. MANETs are vulnerable to various types of attacks including passive eavesdropping, active interfering, impersonation, and denial-of-service. Intrusion prevention measures such as strong authentication and redundant transmission should be complemented by detection techniques to monitor security status of these networks and identify malicious behavior of any participating node(s). One of the most critical problems in MANETs is the security vulnerabilities of the routing protocols. A set of nodes may be compromised in such a way that it may not be possible to detect their malicious behavior easily. Such nodes can generate new routing messages to advertise non-existent links, provide incorrect link state information, and flood other nodes with routing traffic, thus inflicting Byzantine failure in the network. In this paper, we discuss one such attack known as Gray Hole Attack on the widely used AODV (Ad hoc On-demand Distance Vector) routing protocol in MANETs. A mechanism is presented to detect and defend the network against such an attack which may be launched cooperatively by a set of malicious nodes.
The rest of the paper is organized as follows. Section II discusses some related work on routing security in MANETs. Section III defines and discusses various types of gray holes attacks on MANETs. Section IV describes the details of the proposed mechanism for detection of gray hole nodes. Section V presents the simulation conducted on the proposed mechanism and the performance analysis of the scheme. Section VI concludes the paper while highlighting some future scope of work.
The problem of security and cooperation enforcement has received considerable attention by researchers in the ad hoc network community. In this section, we discuss some of these works. Mechanisms for securing the routing layer of a MANET by cryptographic techniques are proposed by Hu et al [1], Papadimitratos and Hass [2], Sanzgiri et al [3] and Yang et al [10]. Schemes to handle authentication in ad hoc networks by trusted certificates authorities (CAs) have been proposed by Zhou and Haas [4]. Hubaux et al [5] have proposed a selforganized PGP-based scheme to authenticate nodes using chains of certificates and transitivity of trust. Some researchers have also focused on detecting and reporting misleading routing misbehavior of nodes. Watchdog and Pathrater [6] use observation-based techniques to detect misbehaving nodes and report observed misbehavior back to the source of the traffic. However, the scheme does not punish malicious nodes; instead, they are relieved of their packet forwarding burden. Researchers have also investigated means of discouraging selfish routing behavior in ad hoc networks, generally through payment schemes [7]. These approaches either require the use of tamper-proof hardware or central bankers to do the accounting securely, both of which may not be appropriate in some truly ad hoc network scenarios. Deng, Li and Agrawal [8] have suggested a mechanism of defense against a black hole attack on AODV routing protocol. In their proposed scheme, when the RouteReply packet is received from one of the intermediate nodes, another RouteRequest is sent from the source node to the neighbor node of the intermediate node in the path. This is to check whether such a path really exists from the intermediate node to the destination node. While this scheme completely eliminates the black hole attack by a single attacker, it fails miserably in identifying a cooperative black hole attack involving multiple malicious nodes.
We first present a security vulnerability in the AODV protocol, and then describe different types of gray hole attacks. In AODV protocol, every mobile node maintains a routing table that stores the next hop node information for a route to a destination node. When a source node wishes to route a packet to a destination node, it uses the specified route if such a route is available in its routing table. Otherwise, the node initiates a route discovery process by broadcasting a RouteRequest (RREQ) message to its neighbors. On receiving a RREQ message, the intermediate nodes update their routing tables for a reverse route to the source node. All the receiving nodes that do not have a route to the destination
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