[ntp:questions] NNTP server causing large jumps in time

David Woolley david at ex.djwhome.demon.co.uk.invalid
Wed May 7 20:35:32 UTC 2008


Dave wrote:
> David Woolley wrote:
ositive and negative steps which approximately balance each other
>> indicate a heavily loaded link with variable and asymmetric 
>> propagation delays.  Apart from local servers, or your Rubidium PPS, 
>> or reducing the traffic, the other solutions are to apply and get the 
>> ISP to apply traffic shaping to prioritise NTP traffic, or to use the 
>> tinker huff and puff option, noting the health warnings attached to it.
> 
> 
> I've changed to local servers as suggested

That wasn't my suggestion.  The usual location of the problem with 
balanced positive and negative steps is the link to your ISP, so using 
UK servers wouldn't make a difference.

You've actually got runs of positive and negative steps, which is 
worrying.  Normally pure runs of postive steps indicate a lost interrupt 
problem.  Runs in a consistent direction and of similar size and 
interval generally indicate that something else is trying to discipline 
the clock.  Alternating steps in positive and negative directions tends 
to indicate an overloaded, asymmetric link, but if you have a severe 
problem you tend to have the server rejected (which is why the problem 
is less common with analogue modems), rather than accumulating a large 
correction.

Missed interrupts may be a problem if runs last long enough for ntpd to 
adapt to the new, effective, frequency.

> 
> server 0.uk.pool.ntp.org
> server 1.uk.pool.ntp.org
> server 2.uk.pool.ntp.org
> server 3.uk.pool.ntp.org
> 




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