Mobile networks are very popular today. But on the other hand there are threats on mobile ad-hoc network. Black hole attack is one of the possible attacks in MANET. Black hole attack is also called packet drop. A black hole attack has become a critical threat. Black hole attack affects the network performance. Gray hole attack is the attack in the network layer. The gray hole attack degrade the performance of network. The variation of black hole is gray hole attack. Gray hole is a node that can switch from behaving correctly to behaving like a black hole that is it is actually an attacker.