More than 90% of the Distributed Denial of Service (DDoS) attack uses TCP [7] so any server that provides TCP- based network like FTP, Web Servers and Mail Server is exposed to TCP-based DDoS attack such as TCP-SYN attack. In this experimental paper, we intend to find out the nature of TCP-SYN attack and evaluate its impact on computing resource of victim computer systems deploying the popular Microsoft’s Windows XP.