TCP Fast Open
Michael Tuexen
tuexen at freebsd.org
Thu Jan 16 19:35:59 UTC 2020
> On 6. Dec 2019, at 15:23, Jeremy Harris <jgh at wizmail.org> wrote:
>
> On 05/12/2019 20:31, Jeremy Harris wrote:
>> On 05/12/2019 20:17, Michael Tuexen wrote:
>>>> - tried TFO but the server didn't take it up
>>> I would expect on = 0.
>>
>> Excellent; that's the most-useful one to know.
>
> Unfortunately, it seems not to be so; it appears
> to be recording the sending of a TFO option
> (of _either_ type; so a cookie-Request still
> gets it set). This means I can't use it to log
> "TFO was actually doing something useful for
> this connection".
> The TCPOPT_FAST_OPEN bit in TCP_INFO says the same
> (either pre-ESTABLISHED or post-).
>
>
> Another problem, this time server-side. I was hoping
> to get the initial server output piggybacked on
> the SYN,ACK, given the TFO design notes in
> https://people.freebsd.org/~pkelsey/TFO_Design_Details.pdf
>
> - but so far I'm not getting that. Packet capture (on lo0):
> SYN -> (TFO=C)
> 0.000224 <- SYN,ACK (TFO=C same value)
> 0.000078 SYN,ACK ->
> 0.001421 <- server_data
>
> The 224us response time for the SYN,ACK looks immediate, not
> a delack time as I'd expect.
A fix is under review:
https://reviews.freebsd.org/D23212
Best regards
Michael
> --
> Cheers,
> Jeremy
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