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 SYN ACK 包，并调用 tcp_output () 将 ACK 包发回到服务器。

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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。

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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。

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