[ntp:questions] Synchronize clocks without a reference clock

Maarten Wiltink maarten at kittensandcats.net
Mon Mar 19 09:38:00 UTC 2007


"Spoon" <devnull at localhost.com> wrote in message
news:45fe5562$0$19562$426a34cc at news.free.fr...

> Consider a cluster of computers on a LAN. These computers have no
> acess to a reference clock (no Internet, no GPS, etc).
>
> One could still want to have all their clocks synchronized, even if
> this means they are all slowly drifting away from the "real" time.
>
> I've read a FAQ which seems to describe this use case.
> http://www.ntp.org/ntpfaq/NTP-s-refclk.htm#AEN4264
>
> All I need to do would be to add these lines:
>
> server 127.127.1.1 # LCL, local clock
> fudge  127.127.1.1 stratum 12 # increase stratum
>
> to my configuration file? Did I understand correctly?

It would work, most likely.

You'd be following a single server's eccentricities, though, and there
are two cases where this could be bad. First, if you've chosen a server
that wanders around rather a lot (say, next to a door), your entire
network will get time that also wanders around a lot. Not a very big
deal, usually.

The other potential problem is that there is a maximum drift that can be
corrected. If the difference between your server and any other host is
larger than that, the client won't be able to follow the server, while
both would be able to follow UTC. This is unlikely but possible.

Orphan mode may be better. It's in the docs, too.

Groetjes,
Maarten Wiltink





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