RE: [chrony-users] Isolated time domains

[Chris Dore <Chris.Dore@xxxxxxxxx>]

On Fri, Dec 6 2013, Miroslav Lichvar wrote:
> 
> On Thu, Dec 05, 2013 at 11:39:17PM +0000, Chris Dore wrote:
> > As an experiment, I've got two instances of chronyd running on a server..
> One instance is sourcing the external ntp servers and taking care of the
> server's local clock.  The second instance, is just serving up the local clock to
> the clients (on a different UDP port).  This is producing what I've been
> describing, although I'm not a big fan of having two instances running since I
> don't understand the chronyd/NTP internals well enough to know of any
> gotchas that may be hiding.  Also, requiring the use of a non-standard port is
> less than ideal, in case an ntp client doesn't support it.
> 
> I think it should work as long as the serving instance doesn't have anything to
> synchronize to. You can change the port in the client instance instead to
> avoid the problem with NTP clients not supporting different NTP port.

I'll give that a shot.

> How close stayed the clients in your test?

My test client running chrony has the following tracking output (poll is currently 8):

Reference ID    : 10.0.0.2
Stratum         : 6
Ref time (UTC)  : Fri Dec  6 16:58:07 2013
System time     : 0.000000421 seconds slow of NTP time
Last offset     : -0.000095257 seconds
RMS offset      : 0.000050311 seconds
Frequency       : 83352.734 ppm slow
Residual freq   : -0.158 ppm
Skew            : 0.102 ppm
Root delay      : 0.002094 seconds
Root dispersion : 0.000188 seconds
Update interval : 258.3 seconds
Leap status     : Normal

The test server currently looks like (poll of 9):

Reference ID    : 192.168.12.68
Stratum         : 3
Ref time (UTC)  : Fri Dec  6 17:51:38 2013
System time     : 3032.924316406 seconds slow of NTP time
Last offset     : 0.000256023 seconds
RMS offset      : 0.000425528 seconds
Frequency       : 24.272 ppm fast
Residual freq   : -0.069 ppm
Skew            : 0.852 ppm
Root delay      : 0.103267 seconds
Root dispersion : 0.039642 seconds
Update interval : 481.7 seconds
Leap status     : Normal

And just to be complete, here's the server's "local-only" instance:

Reference ID    : 127.127.1.1
Stratum         : 5
Ref time (UTC)  : Fri Dec  6 17:10:55 2013
System time     : 0.000000000 seconds fast of NTP time
Last offset     : 0.000000000 seconds
RMS offset      : 0.000000000 seconds
Frequency       : 26.843 ppm fast
Residual freq   : 0.000 ppm
Skew            : 0.000 ppm
Root delay      : 0.000000 seconds
Root dispersion : 0.000001 seconds
Update interval : 0.0 seconds
Leap status     : Not synchronised

As Bill has also pointed out, the high slew rate (approx.. 83300 PPM in my test) is way too high for any ntpd clients to keep up.  I haven't seen a config option, but is there a way to limit the rate in chrony?


Chris


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