VANET or vehicular adhoc network is the type of network in which vehicles move freely in the nework without the help of central controller. Due to its self configuring nature vehicles join or leave the network when they want due to routing, security and quality of service issues may raised in the network. To resolve routing issues in VANET, the three type of routing protocols i.e. : reactive, proactive and hybrid came into existence. In the various researches, it is been analyzed that reactive routing protocols performs well in vehicular adhoc networks. In the study of VANETS, due to decentralized nature of vehicular adhoc networks, many malicious nodes may join the network which is responsible to trigger various type of active and passive attacks. These attacks reduce network performance in terms of network delay, throughput and packetloss.
In the network, two type of communication is possible, the first type of communication is vehicle to vehicle and second type of communication is vehicle to infrastructure. The Sybil attack is the common type of attack which is possible in vehicular adhoc networks. In the Sybil attack malicious nodes change its identification multiple time, due to which on the destination node denial of service occurred which effects network performance. In the recent, times various techniques has been proposed to provide security to vehicular adhoc networks. It is estimated that the first systems that will incorporate VANETS for operating their modes smoothly are police and fire vehicles. This technology will help them to communicate with each other for safety measures.