[ntp:questions] Re: NTP sync on a standalone network (Windows 2k)

David Woolley david at djwhome.demon.co.uk
Thu Aug 17 21:06:40 UTC 2006

In article <44e3a848$0$896$626a54ce at news.free.fr>,
Alexandre Carrausse <alex_s_p_a_m at carrausse.com> wrote:

> 1. 1st question : Is this basic configuration enough?

It is an out of specification configuration because it doesn't have
a proper source of true time.

> 3. Any recommendations regarding the remote servers? Should we peer them 
> with the Central Site?

No.  It is a bad idea to peer servers running with an undiscplined local
clock.  Moreover, all the machines except the central server are leaf
node, so should not have a local clock driver configured.  In cases where
you are dealing with an intermediate node and the advantages of letting
it be a local fall back server outweigh the disadvantages, its local
clock should have a stratum two higher from the machine serving it and
there should be a simple client server relationship.

> 4. Should we peer the server at the central site to keep them more on time 
> (9 minutes drift in one year, but the outside world time is not very 
> important for us)

To what?  As noted above, peering machines with just local clock drivers
is a bad idea.  There should be an unabiguous hierarchy.

One of the disadvantages of using a pure local clock driver is that the
server might have a crystal at the +500ppm limit, which would mean that
any client with a clock with even just a very small negative error would
be unable to synchronise.  Your case is not as bad as this, but as, 
providing you don't lose interrupts, 30 seconds a  year should be possible
in a machine room, you should use ntp.drift to calibrate out the current,
modest, 17.1 part per million error.  (If the people in the thread about
PC clocks is reading this, this is quite typical for PC clocks, but even
several 100 is not uncommon.)

> 7. What is the purpose of the ntp.drift file? What is the meaning of the 
> value contained in this file?

To remember the measured frequency error to allow a fast re-acquisition.

The frequency error in parts per million.

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