in this paper, we make two major contributions for intrusiondetectionsystems (IDS) in MANET. First, we propose a practical and effective messageexchangemodel: DistributedEvidence-driven MessageExchangingintrusiondetectionModel (DEMEM) for MANET. DEMEM overcomes the challenges to Distributed IDS architecture of MANET, where detectors do not have sufficient data to detect routingattacks. Instead of adopting costly promiscuous monitoring, detectors in DEMEM simply intercept routingmessages and validate these routingmessages in order to detectroutingattacks. Also, DEMEM segregates the duties of security agents and routing services to avoid modifying the routingprotocols. The efficient Evidence-driven messageexchange mechanism provides sufficient Evidence in order to perform scalable Distributedintrusiondetection at each node. Second, we integrate DEMEM into a proactiveroutingprotocol in MANET, OptimalLinkStateRouting (OLSR) with four practical assumptions, and three New proposed ID messages specifically for OLSR.The detectionmodel shows that by validating consistency among related routingmessages according to these detectionconstraints, detectors can precisely detect both known and unknown routingattacks in OLSR. We observe that if detectors within two hops can exchange their routing information, they will have sufficient evidence for detectingviolations of constraints. So we propose three ID messages for DEMEM in OLSR to provide the essential ID messageexchange service. IDEvidencemessages guarantee each detector has sufficient evidence for detecting violations of constraints; ID-Forwardmessages trigger the selected forwarders sending ID-Evidencemessages while the detector observes newevidence in order to minimize messageoverhead, and ID-Request handles message loss. Thus, DEMEM not only performs practical, scalable, and accurate intrusiondetection in OLSR but also tolerates message loss with low messageoverhead.