Denial of Service attacks is frequently presenting an increasing threat to the global inter-networking infrastructure in networking area and scenario. The algorithm for Transfer Control Protocol (TCP) congestion control is highly efficient for the various networking areas and operations as well its internal assumption of end-system cooperation results is well prone to attack by high-rate flows. A Shrew attack uses the concept of a low-rate burst which is carefully designed to use the TCP’s retransmission timeout mechanism in an unfair way and can affect the bandwidth of a TCP flow in a smooth manner without coming into appearance as an intruder. A Shrew attack has further classifications such as a low rate shrew attack or a high rate shrew attack. A high rated shrew attack uses the concept of timely sending high rate packet stream in low frequency. Such attack can affect the performance of a network to a large extent.