Vehicular ad hoc Networks (VANETs) are new upcoming technology providing appropriate communication to the vehicles as well as passengers with no fixed infrastructure. In today's life, maintaining the heavy traffic is very difficult that gives bad impact to roads safety and throughput of network. Researchers have done a lot of work in VANET, but still the security got affected from malicious attacks. To maintain the availability, network must be available at the time when vehicles interact with each other. This paper introduces a scheme to detect DDoS attack, as this attack gives adverse effect to network availability. According to our scheme, a Local Protection Node (LPN) is selected from the hierarchical architecture. PDR value and the threshold value has been compared, when these two values become equal a Monitor mode message is to be transmitted by LPN to other vehicles in the network for the purpose of sensing. Any vehicle that injects large number of false packets will be detected as an attacker and thus packets from evil node will be discarded. The proposed scheme is very simple and efficient.

Availability DDoS detection LPN RSU VANET