TCP Fast Open

[Michael Tuexen]

> On 5. Dec 2019, at 20:01, Jeremy Harris <jgh at wizmail.org> wrote:
> 
> On 05/12/2019 18:41, Jeremy Harris wrote:
>> On 05/12/2019 18:28, Michael Tuexen wrote:
>>> sudo sysctl net.inet.tcp.fastopen.ccache_list
>> 
>> Empty content:
> 
> Huh - cancel that.  I re-enabled the setsockopt( TCP_FASTOPEN),
> and now the cookie shows up there, and in SYN options.
> Unsure why it wasn't there before, but never mind.
> 
> Onward to looking at observability.  Under linux I'm having
> to use getsockopt/TCP_INFO, and it doesn't quite do what I'd
> want...
Are you asking how to figure out whether TFO was used or not?
In that case you can use 
getsockopt(fd, IPPROTO_TCP, TCP_FASTOPEN, &on, &len);
If on == 0, TFO was not used, on != 0, TFO was used.

Best regards
Michael
> -- 
> Cheers,
> Jeremy
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