[ntp:questions] Re: Poll frequency

Richard B. Gilbert rgilbert88 at comcast.net
Mon Mar 20 19:31:27 UTC 2006


SivaKumar Subramani wrote:
> I've found some problem in xntpd .
> I would like to know under which scenario the poll value reach to
> 1024, during this time the offset value set
> to too large. Due to this the system clock is not set properly.
> How to avoid or correct this behavior???
> 
> I've copied the output of the ntpq peers command and
> the content of the ntp.conf file.
> 
> ntpq -p
>      remote           refid      st t when poll reach   delay
> offset    disp
> ==============================================================================
> 
>  143.209.150.72  128.252.19.1     2 u  477 1024  377   399.89  -194866
> 15890.6
>  143.209.150.232 143.209.150.72   3 u  508 1024  377   399.69  -193036
> 15890.6
>  143.209.133.66  143.209.150.72   3 u  482 1024  377   399.75  -194566
> 15890.6
> 
> ntp.conf
> 
> server 143.209.150.72   prefer
> server 143.209.150.232
> server 143.209.133.66
> 
> Thanks in advance.
> 
> -Sivakumar
> 
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> questions at lists.ntp.isc.org
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> 

Anything called "xntpd" is several years out of date!!   Upgrade!  (Sun 
and other vendors are still distributing a very old version: V3-5.93e 
which was released around 1998!)  The current version of the software is 
ntpd v4.2.0.  There is a 4.2.1 "release candidate" available for beta 
testing.

Your ntpd output indicates what appears to be an extremely poor choice 
of servers, an extremely poor network connection or both!  The potential 
error in transferring time from server to client is 1/2 the round trip 
delay or over 200 milliseconds in your case.  The dispersion figures 
(some sort off "noise" measurement) are extremely high (something below 
10 would be good).   Finally, the offset figures suggest that your clock 
is in error by more than two days if the value is in seconds.  If it's 
in milliseconds, it's still far to large!!  Ntpd or xntpd cannot correct 
an error greater than 1024 seconds (about 17 minutes).

Set your clock as close as possible to the correct time before starting 
ntpd.  With your version of xntpd, your can use ntpdate to set the clock 
or you can use "date" or whatever command your O/S provides for setting 
the clock.

Choose servers close to you in net space (low delay: MUCH lower than 400 
milliseconds).  If your network connection rather than the choice of 
servers is your problem, try to get a better one.  400 milliseconds is 
long enough to send a signal around the equator at least three times!!!!




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