"Vehicular Ad-hoc NETworks (VANETs) are likely to be deployed in coming years and become the most relevant form of MANET. It is the special class of MANET i.e. mobile ad hoc networks .In recent years not much work has to be done on security. So VANET is used for life saving of passengers. An attacker can change the behavior of other vehicle or infrastructure in the network and also try to challenge the network with their malicious attacks. So in this paper, various detection methods for denial of service attack are discussed."