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SYN attack is a kind of DOS attack. It takes advantage of TCP protocol defects and consumes CPU and memory resources by sending a large number of semi-connection requests. SYN attacks can not only affect hosts, but also harm network systems such as routers and firewalls. In fact, SYN attacks can be implemented as long as these systems turn on TCP services no matter what systems are targeted. As can be seen from the above figure, the server receives the connection request (syn=j), adds this information to the unconnected queue, and sends the request packet to the client (syn=k, ack=j+1), then enters the SYN_RECV state. When the server does not receive an acknowledgement packet from the client, it retransmits the request packet and does not delete this entry from the non-connection queue until the timeout. With IP spoofing, SYN attacks can achieve good results, Typically, clients forge a large number of non-existent IP addresses in a short period of time, SYN packets are continuously sent to the server, and the server replies to the confirmation packets and waits for the confirmation of the customer. Since the source address does not exist, the server needs to continuously resend until it timeout. These forged SYN packets will occupy the unconnected queue for a long time, normal SYN requests will be discarded, the target system will run slowly, and in serious cases, the network will be blocked or even the system will be paralyzed.小葱不语，只瞅着她笑。　　丁亚兰的女儿李珍十六岁，性格活泼，人长得也漂亮，在学校很惹眼。The SYN flooding attack first appeared in 1996. At that time, Phrack magazine described this attack and implemented it in code [1]. This information was quickly applied to attack the mail and Telnet services of a network service provider (ISP) and caused downtime. CERT (Computer? Emergence? Response? Team) soon released a preliminary assessment and solution to this attack technology [2].东环市郊外发现一具被肢解的女尸，重案队全体同志在队长范刚的带领下，经艰苦细致的侦查，找到了被藏匿的受害人头颅和四肢，确定了被害人的身份，锁定了重大犯罪嫌疑人龙飞，可是，在他们取得确凿证据之后，龙飞却被诊断为精神分裂症，不负刑事责任，他们又同包庇犯罪的不法分子展开了更为艰苦的斗争，最终伸张了正义，使罪犯受到应有的惩罚。Recently, I fell in love with stockings and happened to see Stance's sports stockings bought decisively. Because it's a perfect match for my nike? Ha, ha, ha, they are all in the same color system. I remember studying before.