皇帝被囚、宫廷内乱，明枪暗箭 一番龙争虎斗。周家诸人听了，个个笑逐颜开，独有一人言道：就算是真的又如何？周煜这孽畜抛家弃父几十年，枉为人子。In TCP implementation, when receiving the SYN request from the client, the server needs to reply the SYN + ACK packet to the client, and the client also needs to send the confirmation packet to the server. Usually, the initial serial number of the server is calculated by the server according to certain rules or adopts random numbers. However, in SYN cookies, the initial serial number of the server is obtained by hash operation and encryption of the client IP address, client port, server IP address, server port and other security values, which is called cookie. When the server suffers from SYN attack and makes the backlog queue full, the server does not reject the new SYN request, but replies the cookie (SYN serial number of the reply packet) to the client. If it receives the ACK packet from the client, the server subtracts 1 from the ACK serial number of the client to obtain the cookie comparison value, and performs a hash operation on the above elements to see if it is equal to the cookie. If equal, complete the three-way handshake directly (Note: At this time, you don't need to check whether this connection belongs to the backlog queue).
