In our daily life, we face many attacks in the computer field. Some sensitive information we are somewhere stored in secure places like networks and shared devices. With our encryption, our data is not safe from many network attacks and other attacks can be possible. Many attacks are possible to harm data stored anywhere or protect data any layer of security. Many attacks like IP spoofing, Hijacking attack, Black hall attack and DOS attack most popular attack perform on layer 4 NETWORK Layer. This paper discusses the denial of service attack layer number 4(Network).