[ntp:questions] Isolated Network Drift Problem

Cal Webster cwebster at ec.rr.com
Tue Nov 25 22:42:39 UTC 2008

On Tue, 2008-11-25 at 21:10 +0000, Steve Kostecke wrote:
> > Unfortunately, connection to the Internet is not an option I'm allowed
> > to consider.
> Another option you could consider is the dumbclock driver. This uses a
> serial link to transfer time stamps from one system to another.

Thanks but I'm afraid this would be of little use to me since most of
the systems are separated by brick and mortar, connected to each other
through DSL links on site.

> >> The Garmin 18LVC only claims an accuracy of the PPS of about 1micro
> >> second. However getting the time in can be done to the usec level.
> usec == micro second

Thank you. You're very thorough. Although I knew what he meant, others
reading this post may not.

> > I'd like to setup Orphan mode as a backup but I could not determine
> > where to add the command "tos orphan stratum" described at
> > [http://www.cis.udel.edu/~mills/ntp/html/assoc.html#orphan]. It only
> > says to put it in the "configuration file". There is no mention of the
> > "tos" command in ntp.conf(5).
> There is no ordering in ntp.conf. You may place the 'tos orphan N' line
> where ever you wish.

Okay, I'll try that then. I searched the ntp.conf(5) and ntp_misc(5) man
and info pages for "tos" but could find nothing. My only real hint came
earlier today from a set of sample Orphan mode config files I found
during a google search. Coincidentally, it was an archive post from you.


> > When I had previously set up all 4 servers as peers, using local
> > clocks, they would all select the same one.
> This type of fail over is only reliable when the strata of all the
> Undisciplined Local Clocks are correctly staggered.

By staggered do you mean that none may live in the same stratum?

> > When I took that one off-line they selected another. Originally I
> > assumed this was Orphan mode but now I'm pretty sure it's not. I would
> > be grateful if you could clarify this.
> If you are using a 'tos orphan N' line you have configured Orphan Mode.
> If you aren't you're not.
> The Undisciplined Local Clock is not the same thing as Orphan Mode.

Thanks. I think I get it now.

> Orphan Mode provides a way for a group of systems to autonomously select
> a leader in the event that all real time sources are unreachable. A
> group of systems using Orphan Mode are configured as servers to, and
> clients of, each other. Orphan Mode supports all NTP association modes.
> I've personally used it with Unicast, Broadcast, Multicast, and
> Manycast.
> Orphan Mode can also be (mis)used as a Stand Alone server in a
> time-island _if_ you are using a recent enough version of NTP on the
> server. Currently you must be using ntp-dev > 4.2.5p100.

So, if I wanted to setup my 4 NTP servers to look to the one with the
best local clock as the master (if you've been following this thread)
but fall back to Orphan mode when it became unreachable, could you give
me an example of how the configs might look? I could later point them to
the one with the GPS time reference as master when I get it setup.

My main concern is to continue to have an NTP server available in each
of 3 buildings even if they loose connectivity with each other for some
reason. I currently have at least one NTP service running in each
building, serving clients on MS Windows, Linux, and various Unix

Thanks again for your "time". :-)


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