[ntp:questions] Garmin LVC 18x jitter problem

Miroslav Lichvar mlichvar at redhat.com
Mon Aug 19 08:26:42 UTC 2019


On 2019-08-17, Michael Haardt <michael at moria.de> wrote:
> Miroslav Lichvar <mlichvar at redhat.com> writes:
>> I think you do. To prevent the source from being rejected as a
>> falseticker it needs to have a larger root distance. That could be from
>> a larger dispersion or delay. You modified the refclock jitter, which
>> ends up in the peer dispersion (after some weighting). Another approach
>> would be to specify a minimum for the peer dispersion directly. There
>> could be also an option to specify a minimum delay. But adjusting it in
>> the refclock specific code, as you did, makes perfect sense to me.
>
> Which of the alternatives do you prefer? I got one way working, but I
> am willing to test any other in case you have a patch or could at least
> tell me where to enforce the minimum in the code to create a patch.

>From the three approaches I'd probably prefer yours, i.e. keep it as a
refclock-specific option. But maybe see if there is a better name for
the option. "minjitter" might be confusing, at least in my understanding
of the NTP terminology.

If you would like to try the other suggestions, I think they could be
implemented in the clock_filter(), clock_select(), or root_distance()
function.

> In the end, it would be great to get the needed functionality into
> ntpd.

If you want to get it in the ntp code, you should open a bug in the ntp
bugzilla, attach the patch, and see what the maintainers think.

-- 
Miroslav Lichvar



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