In the second section ,we deeply discuss and analyze the theory of SYN Flood attack, memory allocation in TCP 3 hand shakes and different theories of anti this attack, for example ,adoption of syn cookie ,augment of the max value of TCP backlog and etc. .

• 深入地讨论和研究了SYN Flood的攻击原理，在TCP连接时涉及到的内存分配和和对各种防御方法的机理，如采用SYN Cookie，增加TCP backlog等方法，并对其进行了深入地研究。