[Ntp] symmetricom tp1100 stratum and leap indicator behavior

Andy Harrison <aharrison+ntp@gmail.com> Wed, 31 July 2019 19:19 UTC

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From: Andy Harrison <aharrison+ntp@gmail.com>
Date: Wed, 31 Jul 2019 15:19:18 -0400
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Subject: [Ntp] symmetricom tp1100 stratum and leap indicator behavior
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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 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?