A wireless sensor network (WSN) is a wireless network consisting of spatially distributed autonomous devices using sensors to monitor physical or environmental conditions.WSN is a fluorishing network that has numerous applications and could be used in diverse scenarios. DDoS (Distributed Denial of Service) is an attack where a number of compromised systems attack a single target, thereby causing denial of service for users of the targeted system. The flood of incoming messages to the target system essentially forces it to shut down, thereby denying service to the system to legitimate users.Not much research work has been done in DDoS in WSN.We are conducting a review on DDoS attack to show its impact on networks and to present various defensive, detection and preventive measures adopted by researchers till now.