I already have a secondary interface & addresses configured on my servers,
so I was thinking to use it for the second instance instead of using a
non-standard port (which my monitoring software doesn't support)

But how can I configure the server instance it to serve the local time ? if
I don't put any server directive it won't serve ntp, and if i put a server
directive it will serve that time..


2017-09-01 15:47 GMT+02:00 Miroslav Lichvar <mlich...@redhat.com>:

> On Thu, Aug 31, 2017 at 06:48:14PM +0200, Thibaut BEYLER wrote:
> > > You could run a separate server instance of chronyd on a different
> > > port with HW timestamping for the monitoring client. It needs to
> > > support the interleaved mode to be able to get the server's HW
> > > transmit timestamps.
> >
> > Ok i think i understand what you mean, i will try to configure a server
> > instance to see if there is differencies. What source should i configure
> on
> > that instance ?
>
> Just the local clock, e.g. 'local stratum 10' in chrony.conf.
>
> > I tried to force the jitter asymmetry to 0 and got good results again.
> Also
> > with this settings test C are not failing anymore.
>
> The question is if "good" really means more accurate here. I'm still
> not sure what is your reference and how is measured the offset of the
> clients, what timestamping is involved, etc. If the monitoring client
> used DK timestamping, it wouldn't be surprising if DK on the machine
> which is tested gave the smallest offset.
>
> I think a good way to measure the accuracy of the clients would be to
> get an independent stratum-1 NTP server which is known to be accurate
> (e.g. the LeoNTP unit), add a network card which has HW timestamping
> and fast reading of the clock (e.g. i210 or i350) to the client that
> should be tested, connect it directly to the reference server and
> measure the offset on the client with a separate chronyd instance
> configured to not adjust the clock.
>
> Something like this:
>
> Production NTP server ---> Network ---> Client <---- Reference NTP server
>
> > The jitter asymmetry goes especially very fast from 0 to +0.50 with the
> > sources that have hw timestamping, here are some logs just after a chrony
> > restarts for instance :
> >
> > https://pastebin.com/fSHuw7Mx
>
> That suggests some of the timestamps (server's or client's) are not HW
> timestamps, or that the client is not using the interleaved mode when
> it needs to. An HH client with HH server connected to same switch with
> low network traffic in my experience doesn't show any asymmetry. With
> kernel and daemon timestamps that's normal.
>
> A good way to confirm that all timestamps used for synchronization are
> HW timestamps is to check the delay as reported in measurements.log or
> chronyc ntpdata. If you know the the switch adds 20 microseconds, but
> ntpdata shows delay larger than say 30 microseconds (assuming 1Gb
> ethernet), you know something is wrong.
>
> --
> Miroslav Lichvar
>
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