In mobile ad hoc networks, nodes act both as terminals and information relays, and they participate in a common routing protocol, such as dynamic source routing (DSR). Node misbehavior due to selfish or malicious reasons or faulty nodes can significantly degrade the performance of mobile ad hoc networks. We describe the use of a self-policing mechanism based on reputation to enable mobile ad hoc networks to keep functioning despite the presence of misbehaving nodes. In this paper, we investigate the use of an artificial impervious system (AIS) to detect node misbehavior in a mobile ad hoc network using DSR. The system is inspired by the natural impervious system (IS) of vertebrates. Our goal is to build a system that, like its natural counterpart, automatically learns, and detects new misbehavior. Once a misbehaving node is detected it is automatically isolated from the network. We classify the features of such reputation systems and describe possible implementations of each of them. We explain in particular how it is possible to use second-hand information while mitigating contamination by spurious ratings. We implemented the system in the network simulator Glomosim; we present detection results and discuss how the system parameters affect the performance of primary and derivative rejoiner and also misbehavior system is detected and derivative rejoiner is given to eradicate it.