[ntp:questions] Isolated Network Drift Problem

Steve Kostecke kostecke at ntp.org
Tue Nov 25 21:10:29 UTC 2008

On 2008-11-25, Cal Webster <cwebster at ec.rr.com> wrote:

> On Tue, 2008-11-25 at 17:12 +0000, Unruh wrote:
>> "Richard B. Gilbert" <rgilbert88 at comcast.net> writes:
>>> Cal Webster wrote:
>> Or connect your system to the net for a while allowing only ntp
>> packets in or out and use one of the time servers on the net.
> 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.

>> 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

> 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.

> 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.

> 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.

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

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.

Steve Kostecke <kostecke at ntp.org>
NTP Public Services Project - http://support.ntp.org/

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