linux - 绕过 TCP 三向握手？

Question

假设动态提供了正确的 SYN-seq 和 ack 编号，是否可以进行系统调用或编写内核模块以将 tcp 连接直接进入 ESTABLISHED 状态，而无需经过三路握手过程？

Answer 1

您可能想看看 TCP fast open ，现代 Linux 内核实现:

TCP Fast Open (TFO) is an extension to speed up the opening of successive Transmission Control Protocol (TCP) connections between two endpoints. It works by using a TFO cookie (a TCP option) in the initial SYN packet to authenticate a previously connected client. If successful, it may start sending data to the client before the receipt of the final ACK packet of the three way handshake is received, skipping a round trip and lowering the latency in the start of transmission of data.