分布式拒绝服务(DDoS)攻击是当前影响因特网正常工作的一个严重的问题,出现的攻击将会阻止合法的用户使用其所需要的资源。本研究将借助于SSFNet(Scalable Simulation Framework)模拟软件构建相应的网络环境,并模拟了TCP SYN 溢出攻击的全过程。通过调整相关的实验参数设置,给出了在不同攻击强度下被攻击子网的通讯流量图。通过实验可以看出, DDoS 攻击的目的在于耗费被攻击目标机器的资源而使其拒绝提供正常服务,而不是消耗大量的网络带宽。论文还进一步说明了从攻击开始到目标机器瘫痪的时间取决于攻击的强度,即攻击者所控制的发起攻击的机器数量以及发送攻击包的数量。 关键词: 分布式拒绝服务(DDoS);SSFNet;TCP SYN Abstract: The Distributed Denial of Services (DDoS) Attack is a serious issue on current Internet, and frustrates legal users to use some resources they needed. This paper uses SSFNet tools to build network environments, and simulates attack process of TCP SYN. The different network flow graphs are given according to different attack intensity by changing parameter settings in the paper. The target attached by DDoS will consume its resources and provide no services. The period from starting attack to crash of the computer is based on the intensity of attacks which are related to the number of attackers and the number of attack packets. Key Words: DDoS, SSFNet, TCP SYN