[ntp:questions] Re: Linux NTP server problems serving time.

Maarten Wiltink maarten at kittensandcats.net
Mon Jul 18 08:41:56 UTC 2005


"Danny Mayer" <mayer at gis.net> wrote in message
news:42D950C2.7030809 at gis.net...
> Maarten Wiltink wrote:
>> "Danny Mayer" <mayer at gis.net> wrote in message
>> news:42D86196.5050105 at gis.net...

>>> Rule #1 of NTP is that you need at least 3 servers. You only
>>> specified one. It's not going to be able to work this way.
>>
>> Nonsense. I would use a stronger word if you were someone else.
>>
>> NTP disciplines and synchronises a clock. It does this based on
>> information about other clocks.
>
> Right, but you have to have valid information first.

Sure. And I overlooked the bit where the OP had one server plus a
low stratum local clock configured. That must be truly the worst
possible situation, but I reacted to your statement that having a
single (real) server Will Not Work. I still think it will.


>> If it has information about only
>> one other clock, it will simply track it. But this does _not_
>> break the chain to a reference clock.
>
> It's not a matter of breaking a chain, it's a matter of having a
> valid reference in the first place.

And a single server isn't? That doesn't bode well for trying to
construct one from three that, each alone, aren't.

Configuring a single server does expose you to problems that aren't
there with three. But they do not invalidate the setup, and for many
people those new problems will not be the biggest ones they have.

Following a single server leaves you vulnerable to its state of mind.
If it goes insane, you can only follow and probably never even know.
That's *if*, not when. And even if it does, it may not be a big problem.
Your whole site will still have a coherent idea of time, even if it's
five seconds out from UTC.

Network connectivity may be more precarious to a single server than to
a choice of three. But most of us have only a single Internet connection
anyway.

Summarising, you were right that it wasn't going to work "this way".
But "this way" wasn't one server, it was a particularly bad combination
of two. Can you describe a situation where having a single server
really _doesn't work_, rather than aggravating problems that are simply
less pressing with three?

Groetjes,
Maarten Wiltink





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