[ntp:questions] Re: Undisciplined Local Clocks

David Woolley david at djwhome.demon.co.uk
Tue Jan 11 06:48:21 UTC 2005


In article <4E41795B at localhost>,
Allen C <brandy231 at tue2427.cwcom.net> wrote:

> If NONE ran a local clock, then all the servers would lose sync. They would 
> then be unable to serve their clients, and all the clocks in the network 
> would drift apart;

On the other hand, there would be no risk of confusing anyone with
a bogus time, which is why sample ntp.conf's should never have local clock
enabled; it should always be a conscious decision.  That they do is part of
the instant gratification culture.

> and if TWO OR MORE had a local clock then there would be some sort of 
> arbitration and one server would be "elected" leader 

I believe that it is very likely that the network will partition with some
machines using one server and others using the other.  There is no 
sophisticated arbitration.   Generally it is better to have a client 
server tree and set local clock strata at least two apart, so there is
no ambiguity.

> PS   Doesn't an unsynchronised server use the drift file to keep the best 
> time possible?

The drift file is not necessary for this unless ntpd is actually stopped
and restarted.  Also, because the frequency hunts in normal use, the time
will normally diverge faster than if the drift had been calibrated without
using the full protocol.

PS your message ID's risk not being globally unique as anyone creating
an article using the same, weak, algorithm within the same second will clash.
Message IDs are designed to use the host domain name to scope the left hand
part and the left hand part is normally more than just the time.  Absolute
uniequeness is essentail for NNTP to work.



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