Mobile ad hoc networks (MANETs) were originally designed for a cooperative environment. To use them in hostile environments, trust-based routing can be used, where instead of establishing the shortest routes as done in traditional routing protocols, most trusted routes are established. In this study, the authors present a light-weight trust-based routing protocol. It is light-weight in the sense that the intrusion detection system (IDS) used for estimating the trust that one node has for another, consumes limited computational resource. Moreover, it uses only local information thereby ensuring scalability. Our light-weight IDS takes care of two kinds of attacks, namely, the blackhole attack and the grey hole attack. Whereas our proposed approach can be incorporated in any routing protocol, the authors have used AODV as the base routing protocol to evaluate our proposed approach and give a performance analysis.