What is Watchdog Mechanism?

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                         The watchdog method is a strategy proposed before in other studies that detects misbehaving nodes acting alone by maintaining a buffer that contains recently sent packets. When a node forwards a packet, the node’s watchdog ensures that the next node in the path also forwards the packet. The watchdog does this by listening all nodes promiscuously. If the next node does not forward the packet then it is termed as misbehaving. In other words, in this scheme, every packet that is overheard by the watchdog is compared with the packet in the buffer to see if there is a match. A match confirms that the packet has been successfully delivered and it is removed from the buffer. If a packet has remained in the buffer beyond the timeout period, then a failure counter for the node responsible for forwarding the packet is incremented. If this counter exceeds a predetermined threshold then the node is termed as malicious and the network is informed accordingly by a message sent by the node that detects the problem.

We also have developed the Bayesian Watchdog, a tool that merge the watchdog with Bayesian filters. It is more robust agains environmental noise but consume more CPU resources. An adaptation of the watchdog presented above to the Network Simulator 2. It is designed to be use with the AODV protocol of this simulator but can easily adapted to other protocols.

Mobile ad hoc network (MANET) is a self-configuring network that is formed automatically via wireless links by a collection of mobile nodes without the help of a fixed infrastructure or centralized management. Due to dynamic infrastructure-less nature and lack of centralized monitoring points, the ad hoc networks are vulnerable to Black hole Attack. The network performance and reliability is broken by the attacks on ad hoc routing protocols. Many mechanisms have been proposed to overcome the Black hole Attack.


A malicious node or black hole node send Route Response (RREP) incorrectly of having route to destination with minimum hop count and when sender sends the data packet to this malicious node, it drops all the packet in the network. The propose watchdog mechanism detect this black hole nodes in a MANET. This method first detects a black hole node in the network and then provides a new route to source node. In this, the performance of original-AODV and modified AODV called as watchdog-AODV (or W-AODV) in the presence of multiple black hole nodes is find out on the basis of throughput and packet delivery ratio and routing and control load.

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