[ntp:questions] Re: Setting maxpoll interval with 'ntpdc'

Richard B. Gilbert rgilbert88 at comcast.net
Mon Jan 9 23:50:29 UTC 2006


Kevin Golder wrote:

>Well, while playing I found that if you use the ntpdc 'addserver'
>command and place a integer in place of the 'prefer' option it uses that
>as the minpoll value.  If you enter an incorrect integer it spits out
>that you've used an invalid minpoll value.  I didn't see this minpoll
>argument documented anywhere and haven't been successful finding a way
>to edit the maxpoll.
>
>  
>
>>What problem are you trying to solve by adjusting Minpoll  and/or
>>    
>>
>Maxpoll?
>I'm not the end user, so I don't have a good answer for that, expect for
>saying the customer is always right :-)
>
>Kevin
> 
>
>-----Original Message-----
>From: questions-bounces at lists.ntp.isc.org
>[mailto:questions-bounces at lists.ntp.isc.org] On Behalf Of Richard B.
>Gilbert
>Sent: Thursday, January 05, 2006 3:37 PM
>To: questions at lists.ntp.isc.org
>Subject: Re: Setting maxpoll interval with 'ntpdc'
>
>Kevin Golder wrote:
>
>  
>
>>I just have a question about the ntpdc utility.  I can add and delete 
>>servers fine using ntpdc, but how do I edit their minpoll and maxpoll 
>>settings?
>>
>>Thanks for any help,
>>Kevin
>>_______________________________________________
>>questions mailing list
>>questions at lists.ntp.isc.org
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>>
>> 
>>
>>    
>>
>What problem are you trying to solve by adjusting Minpoll  and/or
>Maxpoll?
>
>I don't believe you can, or should do this.   Ntpd selects the poll 
>interval within the range specified by the default values for Minpoll 
>and Maxpoll.  The defaults are correct for most circumstances.   The 
>only exception that occurs to me is a dial-up connection to a server;
>such servers are polled much less often than broadband connections.
>
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>
>  
>
I said "I don't think you can" because, AFAIK, ntpdc does not support 
this.   MINPOLL and MAXPOLL default to 6 (64 seconds) and 10 (1024 
seconds) respectively.  Again AFAIK, the only supported way to alter the 
defaults is via the /etc/ntp.conf file; the server statements support 
MINPOLL and MAXPOLL options.

If you can't educate the customer, then set the MINPOLL/MAXPOLL values 
the way he wants them.   The timekeeping performance of ntpd will almost 
certainly suffer  when compared to the results obtained using the defaults.

An oversimplified explanation of the selection of polling intervals is 
that the lower values are used to correct large errors quickly while the 
longer intervals allow ntpd to correct small errors more accurately.  
Ntpd normally starts polling at 64 second intervals and increases the 
polling interval to an optimum value for the particular situation.  In 
more or less "normal" circumstances the polling interval will be 1024 
seconds or, possibly, 512 seconds.




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