[ntp:questions] NTP with 2 servers

Nuno Pereira nuno.pereira at g9telecom.pt
Mon Feb 23 12:48:00 UTC 2015


> -----Mensagem original-----
> De Nuno Pereira Em nome de Brian Inglis
> Enviada: sábado, 21 de Fevereiro de 2015 01:43
> Para: questions at lists.ntp.org
> Assunto: Re: [ntp:questions] NTP with 2 servers
> 
> On 2015-02-20 16:58, William Unruh wrote:
> > On 2015-02-20, Nuno Pereira wrote:
> >> In our infrastructure we had some ntp clients that don't have access to
the
> >> world and so they are configured to use only 2 servers (by the way, the
> other
> >> have 2 more options). In reality both servers are the same, but with
> different
> >> IPs.
> > So you only have one server. Why have two that are the same?
> >>  From time to time some clients configured in this way lose their
reference
> for
> >> some short period.
> >> I know how NTP works
> >> (http://www.ntp.org/ntpfaq/NTP-s-algo-real.htm#Q-NTP-ALGO), and so
> this seems
> >> to be caused by both 2 servers or just 1 of them not have survived.
> >> But both the clients and the servers are physically in the same place,
and
> >> even if they aren't in the same IP network, they are in the same LAN with
> just
> >> a switch or two between them (delay is between 1 and 2 ms).
> > What is the switch? Smoke signals? Any switch should be a lot lot faster
> > than 1ms.
> >> And the question is why this does happen in the local network?
> >> Aren't they close enough in order to avoid a split?
> >> Given that, I have changed the configuration, and now they only use 1
> server,
> >> but that is not a good solution.
> > But that is what you have!
> >> Any alternative for the configuration? More servers, most likely virtual
> >> servers?
> 
> I dislike the term servers here and prefer sources, as what you need are
> 3-5 independent sources of time. You can get that by setting up NTP on
> some other Internet facing physical servers (Windows, Linux, BSD) whose
> CPUs and network I/O are not overloaded, using pool and/or separate,
> local, independent sources, and have all your internal clients configured
> to sync from all of those internal sources.
> Take care. Thanks, Brian Inglis
Thank you for your interesting answer.
The clients where I have configured just 2 sources (1, in reality) aren't
facing the internet, and so can only use local servers. That can be changed,
but we would prefer to use local servers.
Getting those " some other Internet facing physical servers (Windows, Linux,
BSD) whose CPUs and network I/O are not overloaded" is our problem: we just
don't seem to find them: either our servers aren't, as you say, facing the
internet, or aren't with the CPUs or network I/O overloaded (actually I/O in
general, not network I/O), or may not be.


> You will have to roll patchings across your internal time sources with
> delays to ensure that no more than one source is out of sync at any time.
What do you mean by that?

Nuno Pereira
G9Telecom



 



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