The mobile ad hoc network is vulnerable to many security attacks. They are mainly categorized into two Active attacks and Passive attacks. Active attacks are those which alter the content of packet and thereby disturbing normal functioning of network. Active attacks can be carried out by an external node or an internal compromised node which perform action like impersonation (masquerading or spoofing), modification, fabrication and replication. Passive attacks cannot be easily detected as attacker will not change the content of packet and the network operation is also not affected. These type of attacks violet confidentiality requirement of network communication. The only way to avoid passive attack in MANET is use of encryption to hide the content of packets. These active and passive attacks can be performed at any layer of network. In this paper we are concentrating on attacks on routing in Mobile Ad hoc network. They are Resource Consumption attack, Rushing attack, Black hole attack, Grey hole attack etc. (Singh, 2009).
The Trust based approaches actually not prevent the attack but they detect the attacker node and avoid them in active route. The trust based scheme are also vulnerable to various trust based attacks like Unfair rating attack, unfair rating attack, Sybil attack, new comer attack etc (Lizi Zhang, 2012).