[ntp:questions] NTP client configuration

David Taylor david-taylor at blueyonder.co.uk.invalid
Thu Sep 27 14:47:03 UTC 2012

On 27/09/2012 07:08, Benjamin CABUT wrote:
> Hello,
> We are using Meindberg NTP client and server.
> Our configuration is:
> - 1 Computer under windows that is server
> server
> broadcast minpoll 4 maxpoll 4 iburst
> disable auth
> - several computer under linux + computers under windows, client of this
> server:
> server minpoll 4 maxpoll 4 iburst
> broadcastclient
> disable auth
> My problem is the following:
> Mainly on windows computer, sometime, depending what the computer is
> doing, there is a big offset between clients and server.
> ("Big" for me is more than 500ms).
> I would like to know if it is possible to setup client so as soon as he
> see offset>500ms, then client do a "fast" synch. (STEP).
> Another way to solve my problem could be for me, to modify the source
> code of my application in order to get this "offset" information inside
> my code (C or C++ langage). then I could add this offset to the time of
> the computer in order to be as much accurate as possible during the time
> the offset is bigger than 500ms.
> Do you have any solution?
> Regards.

I haven't used "broadcast" or "auth", so I don't know if that affects 
things.  My understanding of NTP was that unless you configure it 
otherwise, an offset exceeding 128 milliseconds would force NTP to step 
the PC's clock rather than changing the rate, so I am surprised you are 
seeing 500 ms offsets.

I'm using NTP 4.2.7p285 (updated from the Meinberg installation) and 
seeing offsets in the millisecond range (except on a couple of PCs where 
it's the "few milliseconds" range).  This is with three local PCs as 
stratum-1 servers, with a GPS reference.


I would not recommend using the "local clock", and if you need an 
isolated network I suggest looking into "orphan" mode (about which I 
know nothing).

Web: http://www.satsignal.eu

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