[ntp:questions] Looking for a NTP stratum 2 appliance

Paul tik-tok at bodosom.net
Fri May 26 17:13:10 UTC 2017

I also assumed that despite what you wrote you were using your (too few) S1
devices.  I would agree that you probably should not poll NIST at small
intervals for various reasons.  However I suspect that there's a deeper
misunderstanding.  Per NIST the US Federal GNSS system (known as the Global
Positioning System or GPS) can be part of system* that is considered to
produce measurements traceable to the NIST national standards.  Using NIST
servers via the public Internet likely *cannot* produce measurements that
are traceable to NIST (in a meaningful way).

*"GPS disciplined oscillators can be used to establish traceability to the
national time and frequency standards maintained by NIST"  [
Note that NTP fed by a GPS PPS produces a GPS disciplined oscillator.

On Fri, May 26, 2017 at 10:31 AM, Matthew Huff <mhuff at ox.com> wrote:

> We do sync our systems to our stratum 1 servers. The issue is that the
> regulations require us to verify that we aren't 50 msec away from NIST
> time, not GPS time. By running our stratum 2 servers with a preference to
> nist servers and also other ntp servers, our client machines can connect to
> our stratum 1 and 2 servers and we can monitor the diff between the local
> client time and NIST
> > On May 26, 2017, at 9:49 AM, Miroslav Lichvar <mlichvar at redhat.com>
> wrote:
> >
> >> On Fri, May 26, 2017 at 12:11:30PM +0000, Matthew Huff wrote:
> >> Thanks. I agree that the appliance doesn’t appear to exist. It’s a
> shame that it doesn’t, I think it would be a good idea.
> >>
> >> The 50 msec isn’t that hard to reach on an average basis, but we
> routinely see drifts away from that on occasions. The minpoll idea would
> probably fix this, but was hesitant to poll that frequently. I just found
> NIST’s NTP page and they specify to not poll more frequently that every 4
> seconds (minpoll 2). I wouldn’t have thought that they would want polling
> with minpoll 3, but it appears I was wrong. This may fix the issue by
> itself.
> >
> > Using such a short polling interval over Internet would be a horrible
> > idea. NIST servers are overloaded and located in a network that has
> > problems with asymmetric routing. It's better to avoid them if
> > accuracy is a requirement. I thought you were using those stratum-1
> > servers you have and the requirement for accuracy was 10 or 100
> > microseconds, not milliseconds.
> >
> > Anything should do better than 50 milliseconds as long as it's on
> > local network.
> >
> > --
> > Miroslav Lichvar

More information about the questions mailing list