[ntp:questions] ARRGH!!! I woke up to a 50 SECOND clock error.

Ron Frazier (NTP) timekeepingntplist at c3energy.com
Sat Mar 17 18:27:31 UTC 2012

On 3/17/2012 11:48 AM, David J Taylor wrote:
>> You'd get less jitter with DSL.
>> -- 
>> John Hasler
> John,
> You have piqued my interest.  I have just set up a Windows-8 PC with 
> an ntp configuration not dissimilar to Ron's, in that it's using 
> purely Internet servers but trying to monitor a local stratum-1 server 
> as well. In essence:
> ______________________________
> # Local stratum-1 Free BSD server
> server  iburst  minpoll 5 maxpoll 5  prefer  noselect
> # Seven external servers:
> server  x.x.x.uk  iburst
> server  y.y.y.uk  iburst
> server  0.uk.pool.ntp.org  iburst
> server  1.uk.pool.ntp.org  iburst
> server  2.uk.pool.ntp.org  iburst
> server  0.nl.pool.ntp.org  iburst
> server  1.nl.pool.ntp.org  iburst
> ______________________________
> The performance will appear here:
>  http://www.satsignal.eu/mrtg/performance_torvik.php
> It will be interesting to see whether the Internet servers poll period 
> increased from 64s (I'm hoping that the 32s poll on the local server 
> won't affect the Internet ones), and what level of jitter is achieved.
> Cheers,
> David

Hi David,

I'm not sure what will happen if you simultaneously prefer and noselect 
the local server.  Assuming the local stratum 1 server is the most 
stable time source, you'll get a much better picture of what the 
internet servers are doing relative to it if you allow it to be 
selectable as well as being preferred.  When you graph it, if the local 
server is the active clock, all the lines for the internet servers will 
be gathered around and relative to the local server.  When I tried to do 
things the other way around, with an internet server preferred, the 
graph looked awful because there was so much variation.  Also, if your 
local server starts reporting time that looks too far from the internet 
servers, regardless of who's fault it is, ntp will clock hop over to the 
internet servers.

I don't THINK your internet servers will ever poll above their default 
minpoll value of 6, or 64 seconds.

I realize you don't have a gps attached to this pc, but the iburst lines 
reminded me of something.  I read somewhere that having iburst on 
internet server lines, if a local gps is attached, could prevent the PC 
from synchronizing to the gps before it synchronizes to the internet.  
On my pc with the gps attached, I don't use the iburst command.




(PS - If you email me and don't get a quick response, don't be concerned.
I get about 300 emails per day from alternate energy mailing lists and
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Ron Frazier
timekeepingdude AT c3energy.com

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