In this paper, the authors analyzes the gray hole attack which is one of the possible attacks in ad hoc networks. In this they are mainly focus on the impact of gray hole attack on ad hoc network & also find its consequences. An ad hoc network is a collection of mobile nodes that dynamically form a temporary network and are infrastructure less. The first is known as the \"Infrastructure network\" (i.e. a network with fixed and wired gateways). The bridges for these networks are known as \"Base stations\". A mobile unit within these networks connects to and communicates with the nearest base station that is within its communication radius.