[ntp:questions] symmetricom tp1100 stratum and leap indicator behavior
unruh at invalid.ca
Fri Aug 2 13:07:58 UTC 2019
On 2019-07-31, Andrew Harrison <aharrison at gmail.com> wrote:
> The backstory... I've been tasked with deploying a pair of Symmetricom TP1100 Time Providers with GPS antennae as the official time source for the company (replacing an ancient server with a Meinberg card in it). My company actually purchased the Symmetricoms a few years ago, but they never got around to putting them in production. No one was able or willing to put in the time to get them going. I started working at the company recently and they gave the project to me.
> I've got them up and running and my test ntp client (my Linux workstation running ntp 4.2.8p12) can pull time from them just fine.
> Now for the hard part. What we want to happen is that if the GPS of the primary Symmetricom goes offline, we want the clients to start getting time from the backup unit.
> Ideally what would happen is the GPS goes offline, the Symmetricom would set itself to a higher stratum level and the clients abandon it for the device that has the better stratum, but this is not what happens.
I think that the problem is that if ntpd gets invalid packets, it simply
ignores them (as it should because missing a few packets is standard
behaviour) It simply free runs on the last good packets to come in,
since it has nothing else to go by. Apparently it is not actually using
the second device while the first is working ( and besides, it would
have a hard time deciding which was good and which not).
Have you tried using both of the symmetricons as sources always. Then
there is a change that if one goes offline, the other one will
automatically get picked as the source?
Or perhaps you could query the machines, or the symmetricons, to see if
they have gone nuts (invalid stratum) and then have that program do the
substituting for you (by sending ntpd a change of source)? Ie, you have
a second program being the scount to see whether the data coming in is
> I had to use Wireshark to see that instead, when the GPS goes offline, the Symmetricom stops advertising a stratum level (Wireshark shows "unspecified or invalid") while the leap indicator shows "clock unsynchronized" (3 I think it was). (When I enable the GPS again, Wireshark shows the stratum level coming through as 1 and leap indicator shows 0 "no warning".)
> On my workstation test client, ntp apparently doesn't know what to do when a time source stops indicating its stratum level so it keeps right on showing stratum 1 in ntpq output even though Wireshark clearly shows the packets coming through with stratum level "unspecified or invalid".
> So, my question is, can I configure ntp in such a way that it responds to either a lack of advertised stratum or a leap warning indicator greater than 0?
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