On 08/01/19 12:43, Terje Mathisen wrote:
Chris wrote:
On 07/31/19 20:10, Andrew Harrison 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 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?
Thanks!
If you have 2 servers, both gps, then the polling host needs to
have config to allow fallback to the second unit when it fails.
Not a time server issue afaics, unless each has fallback ability in
itself.
What you could do is run ntpd on a third host, polling both time
servers along with a host or two from an ntp pool, which should have
the ability to spot the outlier and continue providing accurate time.
Not sure about the overall behavior, but wouldn't take long to set
it up and check results...
Chris
I ran the ntp setup for Norway's largest multinational corporation for
20+ years, my final setup used dedicated TrueTime/Symmetricom/Meinberg
gps-based servers in 3 main locations, augmented with radio-based clocks
in a couple more as well as several hand-made FreeBSD servers using
Oncore and SURE evaluation boards with timing gps receivers.
Sounds like fun.
All these primary sources were used as references for a second layer of
dedicated Stratum 2 servers, two in each of those 3 main geographical
centers, and with identical/symmetrical conf files. The latter works
because an ntpd server automatically omits any circular reference, to
itself or another source.
Finally, every single client machine capable of running the full ntpd
stack was configured to use all 6 Stratum 2 servers as their reference,
this provided enough redundancy that we never suffered any visible
hickups even when we passed through the GPS week rollover or when an
individual reference server lost a leap second event.
Except for the hardware ref servers, this was all effectively close to
zero cost, only some labor hours.
Terje
Not so ambitious, but trying to do the same sort of thing in the
experimental setup here. A bit of a newby with ntp, but have used
ntp on machines for years. Also gps based 10MHz frequency
standards for the lab test gear. Consider redundancy pretty much
essential and even with a set of local hardware time servers,
would always include some ntp pool entries, if only as a sanity
check for the local hardware. If you work it through another host,
ntp should do all the hard work for you anyway, the algorithms
deciding which are the most accurate subset and automatically
rejecting outliers.
One thing from the op's post is the apparent reversion to
stratum invalid, which suggests an out of lock gps condition.
What i've found with older gps receivers is that the antenna
often needs a clear view of the sky for best performance, or
even to lock at all, so a window ledge antenna solution may not
be good enough...
Chris
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