Intrusion Detection Systems (IDSs) for Mobile Ad hoc Networks (MANETs) are necessary when we deploy MANETs in reality. In this paper, we focus on the protection of MANET routing protocols. Therefore, we present a new intrusion detection architecture based on quantitative, agents, and clusters that is suitable for multi-hop mobile ad hoc networks. It detects nodes misbehavior and anomalies in packet forwarding such as dropping, modifying or delaying of packets by intermediate nodes. Simulation results are given to validate the efficiency of our IDS architecture in detecting intrusions and reducing false positive rate.