—Collaboration between nodes in Mobile Ad hoc Networks (MANETs) is very important for the proper functioning of the network. This is an assumption that has to be fulfilled in the design of routing protocols. However, this is not always true since some nodes could misbehave in order to have some benefits or simply avoid wasting resources. In this paper we question this assumption that does not take into consideration the bad behavior of nodes involved in the routing protocols. We analyze the characteristics of the existing solutions, and we propose a reputation-based mechanism that isolates selfish nodes based on control packets generated as a result to nodes' observations on the behavior of other nodes. We propose a mathematical framework to increase/decrease the reputation of a node depending on the situation and the observation condition. We show via simulation that our solution achieve remarkable improvements in the delivery rate of packets, more than satisfying results concerning false positive and false negative, and it shows that the overhead caused by our system is negligible.