Mobile ad-hoc communication is a spontaneous network because the topology is not stationary but self-organized. This requires that during the time MANET it operational, all the processes regarding discovering the topology, delivery of data packets and internal management communications must be taken care by the node(s) themselves. This implies the criteria for selection of Cluster Head (CH) and the routing related protocols are to be integrated into mobile node(s).The very facts that MANET is challenging and innovative areas of wireless networks, makes it more vulnerable in term of routing and flooding attacks. In this paper, a node trust calculation methodology is proposed which calculate the trust value of each node and applies fuzzy logic to detect wormhole, Black-hole (Routing attack) and distributed denial of service attack (DDOS/Flooding) in dynamic environment.