[ntp:questions] Re: Getting good NTP tracking

Eino-Ville Talvala quantumet at gmail.com
Tue Jun 27 17:44:55 UTC 2006


Richard B. Gilbert wrote:
> David Woolley wrote:
>> In article <jJqdnWKEcajxyT3ZnZ2dnUVZ_o-dnZ2d at comcast.com>,
>> Richard B. Gilbert <rgilbert88 at comcast.net> wrote:
>>
>>
>>> Look at your /etc/ntp.conf.   In that file, look at the server 
>>> statements.   Do they include the keyword MINPOLL?  Or MAXPOLL?
>>
>>
>> He included it in his original posting and it has been (over) quoted
>> several times since.  He had no minpoll or maxpoll.  It's really not
>> uncommon for the poll interval to stick at the maximum once the system
>> has stabilised.
> 
> Sorry, I missed that, or thought he missed it.  He didn't cut and paste 
> it.  His complaint seems to be that he's getting large offsets and that 
> suggests to me that the system has NOT stabilized.
> 
> Requoting the the numbers we're talking about:
> peers.20060620
>        ident     cnt     mean     rms      max     delay     dist     disp
> ==========================================================================
> <UNIVERSITY>     132   -4.089   90.922  986.193    4.340  939.038   30.380
> 
> The University server seems to have been polled only 132 times in 24 
> hours while the maximum offset is 986.193 milliseconds.  I've used a few 
> servers that looked that bad and the polling interval did not get very 
> large.  The picture suggests a network problem of some sort which I find 
> a little surprising since the network he describes would seem to be a 
> LAN or a small WAN (note the small value of delay).
> 
> My NTP experience has been almost entirely with 10-base-T and 100-base-T 
>   switched full duplex technology.  If he has 10-base-5 (thick coaxial 
> cable) or 10-base-2 (thinwire) or even twisted pair with hubs instead of 
> switches he could be getting enough phase noise from his network to 
> force a long poll interval.

This is actually on GigE, at least in my building - I'd assume the 
campus backbones are probably all GigE by now, certainly 100-base-T. 
The departmental NTP server should be in the same building with me, at 
least.

I could certainly simply have one machine use an undisciplined local 
clock and point the other at it as the sole timing source, but when I 
tried that earlier, I didn't have any better luck in maintaining good 
tracking.

I haven't yet collected enough data to tell if disabling SELinux and 
adding more servers will help - hopefully those will do the trick.




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