In this paper, the authors provide detailed of attacks on peer-to-peer network with their suitable defensive technique or algorithm. They try to reduce the effect of Sybil attack from P2P network. In Peer-To-Peer (P2P) network is a way of structuring distributed applications such that the individual nodes have symmetric roles. Peer-to-peer network having no any hierarchy that means all peers are equal and no administrator responsible for the network. There are a several kinds of attacks in peer-to-peer network. Like DOS attack, DDOS attack, rational attack, Sybil attack and eclipse attack.