Abstract: Mobile ad hoc networks (MANET) has risen as a major next generation wireless networking technology. This network is a network of mobile nodes with dynamic structure. Here each node acts as a router for forwarding data to other nodes. Due its dynamic nature, security has become a primary concern to provide protected communication between different nodes in ad hoc networks. There are a number of challenges in security design as ad hoc network is a decentralized network. There are five layers in MANET and each of these layer is vulnerable to various attacks. In this paper we discuss about various attacks and their protection mechanisms.

Keywords: MANET