Vehicular Ad hoc Networks is used for communicating with nearby vehicles and between vehicles and nearby fixed equipments. VANET is also a kind of MANET. VANETs are mainly used for improving safety and efficiency of (future) transportation. There are many chances for the possible attacks in VANET due to open nature of wireless environment. There are different types of attacks in the wireless medium. In this paper, we have discussed about the attacks in the VANETs. We have also proposed the solution for the attacks by providing Authentication in the VANET by using Virtual Certificate Authority among the vehicles. Also, an efficient solution is being proposed for Denial of service (DOS) based attacks which uses the redundancy avoidance mechanism consists of rate of decreasing memory among the vehicles. This solution will basically add more security to the already existing solutions of using various alternative options like frequency-hopping, channel-switching, communication technology switching and multiple-radio transceivers to counter affect the DOS attacks