Network security has become more necessary to personal computer users, organizations, and the military. With the advent of the internet, security became a major concern and the history of security sanctions a better understanding of the emergence of security technology. Network attacks had become a curse to technology, where attacker destroy or gain illegal access to system recourses and restrict the legitimate users from accessing the information. In this paper, we are going study different type of network security attack and learn counter measures for that attack. We are also going to study different techniques to detect such attacks.