Most of the networks are generally protected using firewalls and encryption techniques. But many of them are not sufficient and effective. With the propagation of computer networks extending boundaries, MANET has emerged as a new frontier of technology to provide anytime, anywhere communication. Absolute security is very hard to achieve in MANET because of its fundamental characteristics such as dynamic topology, open medium, limited power and bandwidth capabilities. Therefore an Intrusion Detection System (IDS) is required to monitor the network, detects anomalies and notifies other nodes to avoid or punish the misbehaving node.