[ntp:questions] Time Islands (Was: Re: Fwd: [ntpwg] RFC 5905 ... )

Steve Kostecke kostecke at ntp.org
Thu Jun 24 20:53:40 UTC 2010

On 2010-06-24, pc <Paul.Croome at softwareag.com> wrote:

> Many users of this list have a requirement to synchronize a number of
> machines within some user-defined limit, but they don't care if they
> are all offset from UTC by a few minutes.

The problem is that most time island operators appear to make the
unstated assumption that ntpd is a magic box which will make all of
their clocks tick at 1 second per second.

> Time islands would seem to be a common use-case, and it's my opinion
> that the RFC's assertion that genuine NTP networks must be based on
> UTC is an unnecessary restriction.

A "genuine NTP network" needs a stable reference source. Each ntpd in
the network steers its node clock to bring it as close as possible to
the reference. Otherwise you have a herd of kittens playing follow the

UTC is a ubiquitous stable reference source which is usually cheaply
available via a network or an inexpensive timing GPS receiver.

Other stable reference sources, such as a Rubidium disciplined PPS
generator, are also suitable.

Steve Kostecke <kostecke at ntp.org>
NTP Public Services Project - http://support.ntp.org/

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