Detection and Ignoring of Blackhole Attack in Vanets Networks

2. The Aodv Routing Protocol

The AODV protocol is the most widely adopted and well known reactive routing protocol in which routes are created only when they are needed (Ochola EO & Eloff2011). The mobile devices or nodes in the network exchange the routing packets between them when they want to communicate with each other and maintain only these established routes (Ei Khin and Thandar 2014). The AODV routing protocol in an adaptation of the DSDV (Destination-Sequenced Distance Vector) protocol to get dynamic link conditions (E. Perkins & Elizabeth-Royer 2003). Whenever a node wants to send the data packet to another node, it checks its routing table. If it has a fresh route to the destination node, it uses that route to send the data packet. If it does not have a route or it is not fresh enough route, then the node starts the route discovery process. So, it broadcasts Route Request message (RREQ) to its neighbors. The intermediate nodes check whether it is the destination node or it has a fresh route to go to the destination node. If it is available, the intermediate node sends back Route Reply message (RREP) to the source node. Otherwise, it forwards the RREQ message to its neighbors by using flooding approach. This process is repeated until either the destination node or a node that has a fresh enough route to the destination is found. After finishing the route discovery process, the source and the destination node can be communicated and exchange packets between them. When any node detects a link break or failure, a Route Error (RERR) message is sent to all other nodes to notify the loss of link. Hello message is used for detecting and monitoring links to neighbors (Nital Mistry, Devesh.c 2010). Figure 1 illustrates the function of the routing protocol AODV.

Figure 1.

RREQ and RREP packets in AODV

External node can attack by following way (Mr. Ravi, Ms. Khushbu, 2005)(Y.-C. Hu, D.B. Johnson 2002).