VANET (Vehicular Ad-hoc Network) has become a remarkable and emerging area for research analysis and development. VANET is a subgroup of MANET (Mobile Ad-hoc Network). VANET and MANET both are wireless networks which are characterized as self-configured and autonomous ad-hoc networks. The main objective of VANET is to builds a robust network between mobile vehicles so that vehicles can talk each other for safety of human beings. Vehicular communication systems developed largely by the growing interest in intelligent transportation systems (ITS). Due to rapid topology changing and frequent disconnection makes it difficult to design an efficient routing protocol for routing data among vehicles, called V2V or vehicle to vehicle communication and vehicle to road side infrastructure, called V2I. In this Paper mainly focus on topology based routing protocol and analysis of reactive routing protocols based on their advantages and disadvantages for the routing mechanisms that exist in VANETs.