Abstract: Mobile Ad hoc network (MANET) is gaining more importance and popularity due to the proliferation of miniature yet powerful mobile computing devices. MANET is more vulnerable due to its networks characteristics, such as dynamic topology, distributed cooperation and open medium. Ad hoc On demand Distance Vector (AODV) protocol is the most popular reactive routing protocol designed for the MANET. AODV is vulnerable to both external and internal security attacks. In this study, we analyze the vulnerabilities of AODV protocol, specifically the internal attacks and we propose solutions to monitor the attack by using an Intrusion Detection System (IDS). Our solution is based on a Fuzzy Based Response Model (FBRM).