Re: Mysterious 3 and 9 second delays calling connect()

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On 21/10/10 21:06, Mark Doliner wrote:
> For the first three connections the client sends SYN, server
> immediately replies with SYN ACK, then clients sends ACK then FIN ACK.
>  The server does NOT respond with FIN ACK.  I've been assuming that
> this behavior is expected.  Perhaps FIN ACK will not be sent until the
> server process has called accept()?

FIN ACK will not be sent until the server has accepted socket AND called
close or shutdown to close the socket. Each TCP direction can be closed
independently.

> Here's the part I don't understand: For the fourth connection the
> client sends SYN, but the server does not respond (neither with SYN
> ACK nor RST).  The client resends the SYN after 3 seconds.  Sometimes
> the server will respond with SYN ACK and things continue normally.
> Other times the server will ignore this second SYN, the client waits 6
> more seconds and resends the SYN, to which the server will always
> reply with SYN ACK.

I don't know for sure but this sounds like denial-of-service avoidance
code kicking in.

Regards,
Dimitrios Siganos
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