In a MANET number of devices or mobiles are connected to each other with wireless medium. This network is a temporary network. In the MANET, there is not any centralized device which control all netwrok. MANET using dynamic topology. The Sybil attack is characterized as a malicious node misguidedly taking on various MANET . A Malicious device acts as though it\\\'s anything but a bigger number of nodes, for instance by mimicking different devices or basically by asserting bogus MANET. In this,a terrible device present more than one character in MANET. So it is not much safe Network. The attacker are easily attacks on the MANET. Consequently, Security is an essential worry to give ensured correspondence between nodes in impromptu organizations and shots at having the weaknesses are additionally more. In this paper we complete analysis and classification of the various Sybil attack techniques and decline the network performance and throughput.