In normal operation, the remote client responds with an ack packet that moves the half-open connection to fully open.
在正常操作中，远程客户机用一个ACK数据包进行响应，这会使半开的连接转换为全开的。
The tcp_input () routine on the client side processes the SYN ACK packet, and calls tcp_output () to send an ACK packet back to the server.
客户端上的 tcp_input ()例程处理SYNACK包，并调用 tcp_output ()将 ACK 包发回到服务器。
An attack called the SYN flood ensures that the ack packet never returns so that the server runs out of room to process incoming connections.
有一种称为syn泛滥(SYN flood)的网络攻击，它使ack数据包无法返回，导致服务器用光内存空间，无法处理到来的连接。
When a new TCP connection comes in from a client by means of a packet with the SYN bit set, the server creates an entry for the half-open connection and responds with a SYN-ACK packet.
当从客户机发来新的TCP连接时，数据包设置了SY n位，服务器就为这个半开的连接创建一个条目，并用一个SYN -ACK数据包进行响应。
The server will acknowledge this by returning a packet with the ack flag set.
服务器将通过返回设置了ACK标志的包进行确认。
If the port is not open, the scanned host sends a packet with the RST and ack flags set.
如果端口未打开，则被扫描主机发送设置了rst和ack标志的包。
The server answers with a packet where both the SYN and ACK flags are set.
服务器以设置了 SYN和ACK 标志的包应答。
In response, the scanned host returns a packet with the SYN and ack flags set if the port is open.
如果该端口是打开的，则被扫描主机返回设置了syn和ack标志的包进行响应。
Finally, the client confirms this by sending a TCP packet back to the server with the ack flag set.
最后，客户机通过向服务器发送设置了ACK标志的tcp包进行确认。
If the ack is from the expected node, the retransmission of the packet is cancelled.
收到一个应答时调用。如果应答是期望的节点，将取消数据包重发。
If the ack is from the expected node, the retransmission of the packet is cancelled.
收到一个应答时调用。如果应答是期望的节点，将取消数据包重发。
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