compared to the wired network. The requirement of prior information regarding the broadcast feature and protocols required for reliable communication for MANET. Device mobility and frequent topology change is another important challenge. Further, its limited Processing capabilities, memory storage, energy and bandwidth are the required for algorithm implementation in MANET. MANETS [2] are vulnerable to attacks than its counterpart wired network. Vulnerabilities actors in Ad hoc networks are Absence of integrated observing and management, limited battery backup, power supply, infrastructure-less network with limited resources, frequent disconnections and partitions due mobility. Due to the above vulnerabilities, MANETS have to accomplish security goals. The major network security goals are confidentiality, and authentication. While compared to integrity, authorization availability and non-repudiation. In MANET, a number of communication approaches among nodes approaches are unicasting, multicasting, broadcasting, geo-casting and converge casting. These approaches are useful for successful communication in MANET. But, the characteristics and communication approaches of MANET present problems for achieving challenges and the security goals. Trust management is required to betterment the secrecy and security of MANET. The service of Watchdog is to monitor routing nature of a node, and then feed the information into the reputation system to manage and maintain the node reputation and thereby detection of black hole attack. The advantage of the watchdog is that it needs only local information for the detection of malicious node. A. Passive and active attackThe attackers may delay the message/packets from reaching the destination, drop the packets or change the messages. The attacks are listed into two classification, viz. passive and active attacks. The passive attackers indulge in monitoring or eavesdropping of data, during the transmission of data in the network. The attackers do not attempt to tamper or modify the data in transit. Detection of passive attack is difficult, hence passive attacks need to be prevented rather than detecting and taking corrective actions. In other words, passive attacks do not indulge modifications to the original message contents. Passive attacks are further sub classified into two categories. First is release of message contents, where the sensitive information from the data are monitored during its transit. And the second type of attack is traffic analysis, here attackers may not get access to the data, but may know when and from where the message was transmitted from. This is used for predicting the nature of the information. Active attacks, on the other hand, involves modification or tampering of messages on the transit. Prevention of active attacks is very difficult. Active attacks comprises of Denial of Service Attack (DOS), Replay attack, Masquerading, and alteration. The black hole is an example of an active attack. Where in the attacker drop the packets which are received. Two ...