GANDHI & DAVE : SECURITY IN MOBILE AD HOC NETWORKS
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after sending the packet to next hop, say node B; the sender tries to overhear the next node B transmitting the packet again to its next hop, say node C. It is to be noted that node B is in the radio range of node A and so A is able to hear B’s broadcast. When a node is unable to deliver a packet to the next node even after retransmissions then the node sends a Route Error (RERR) message to the original sender of the packet. The source node then either uses an alternate route present in the cache or may initiate a fresh route discovery procedure in case the cache is empty.

(b) Ad hoc On-Demand Distance Vector Routing (AODV)

The AODV routing protocol [1,7] is based on DSDV and DSR algorithm. It uses the periodic beaconing and sequence numbering procedure of DSDV and similar route discovery procedure using RREQ and RREP messages as in DSR. There are two major differences between DSR and AODV. The most important difference is that in DSR, each packet carries the full routing information, whereas in AODV the packets carry the destination address only. This means that AODV has potentially less routing overheads than DSR. Every node in the network maintains a routing table in which next-hop routing information for destination nodes is stored. The other difference between AODV and DSR is that the route replies in DSR carry the address of every node along the route, whereas in AODV the route replies carry the source IP address, destination IP address, the destination sequence number as given by a node’s routing table entry for the destination and hop count (distance) from the destination of the node which is forwarding the RREP message. The hop count field is incremented by one every time a node forwards the RREP message towards the source.

The advantage of AODV is that it is adaptable to highly dynamic networks. However, nodes may experience large delays during route construction, and also link failure may initiate another route discovery, which introduces extra delays and consumes more bandwidth.

2.3. Hybrid Routing Protocols

Hybrid Routing Protocols [4] are a new generation of protocols, which are both proactive and reactive in nature. These protocols allow the nodes with close proximity to work together to form some sort of backbone, thus increasing scalability and reducing route discovery to determine routes to far off nodes.

 

Zone Routing Protocol (ZRP) [8] is a popular hybrid routing protocol. In ZRP, each node has a routing zone, a range (in hops) in which each node is required to maintain network connectivity. Thus for the nodes in the routing zone, the routes are directly available i.e. proactively whereas, for nodes lying outside the
routing zone, routes are determined on-demand. The amount of communication overhead is thus greatly reduced.

3. ROUTING SECURITY IN MANET

Every node in MANET acts as a router that discovers and maintains routes to other nodes in the network. Efficient routing of packets is a primary MANET challenge. Various protocols have been proposed for efficient routing. However, there are several challenges to ensure secure routing in MANET as mentioned below:

  • All signals go through bandwidth constrained wireless links, which makes them more prone to physical security threats than fixed networks.

  • As the mobile nodes move independently of each other and may move in any direction, a security solution with static configuration would not be adequate for frequently changing topology.

  • Decentralized decision making in MANET relies on the co-operative participation of all nodes. The malicious node could block or modify the traffic traversing it, by refusing co-operation thus breaking the cooperative
    algorithms.

  • Most of the nodes rely on batteries or other exhaustible means for their energy. An attacker could cause the replaying of packets in the network leading to the exhaustion of energy in the nodes.

3.1. Security Attacks on MANET

Security implies the identification of potential attacks, threats and vulnerability of a certain system. The attacks on the MANET can be broadly classified into passive and active attacks [9-12].

Passive Attacks

The attacker in these attacks does not actively participate to bring the network down. This attack does not disrupt the operation of a routing protocol and the attempt is to discover valuable information by listening to the routing traffic. These attacks (also known as routing attacks) are very difficult to detect
[10].