google
Netstack should retransmit a SYN immediately after a challenge ACK from peer.
Description
Linux always retransmits the SYN immediately when a peer sends a challenge ACK. This makes sense since the peer by issuing a challenge ACK is letting us know of a TIME-WAIT socket on its end. Sending a RST will clear the state and retransmitting the SYN shortly thereafter will complete the connection. There is no reason to wait for a full 1s initial timeout in this case as the original SYN wasn't lost.
Not doing it just incurs additional latency as we wait for the connect retransmit timer to fire which can take upto a second.
Specifically the RST sent here should be followed by a SYN retransmit after a short time. https://github.com/google/gvisor/blob/ad8960f60401953f9d57809bc3add378487bf039/pkg/tcpip/transport/tcp/connect.go#L293
and the equivalent linux code is here
https://github.com/torvalds/linux/blob/249aca0d3d631660aa3583c6a3559b75b6e971b4/net/ipv4/tcp_input.c#L6170
Steps to reproduce
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