[ntp:questions] Number of Stratum 1 & Stratum 2 Peers

Harlan Stenn stenn at ntp.org
Sat Dec 13 03:07:02 UTC 2014


Bill,

I'm done trying to have a productive discussion with you about this.

H

William Unruh writes:
> On 2014-12-13, Harlan Stenn <stenn at ntp.org> wrote:
> > William Unruh writes:
> >> On 2014-12-12, Harlan Stenn <stenn at ntp.org> wrote:
> >> > Mike,
> >> >
> >> > I think you are seeing the correct and expected behavior.
> >> >
> >> > The root cause here is that the majority of the upstream servers are
> >> > *incorrectly* not advertising the leap second.
> >> >
> >> > There have been problems before where a misconfigured server has
> >> > incorrectly advertised a non-existent leap-second, and in cases where
> >> > folks had an adequate number of correctly configured servers, this
> >> > mistake was properly ignored.
> >> >
> >> > I have not been closely following this thread, so I might be missing
> >> > something.
> >> >
> >> > It's pretty easy to download and install a leapsecond file, and ntpd
> >> > will pay attention to that...
> >> >
> >> > Or am I missing something?
> >> 
> >> Yes, That it was an example of a case in which the correct time server
> >> could be declared a falseticker. The answer you give "never use sources
> >> which might not deliver the correct time" does not obviate the point. 
> >> The concept of "falseticker" and of "bad time" are not the same thing. 
> >
> > Nobody is saying "never use sources which might not deliver correct time."
> >
> > Aside from that:
> >
> > - what is the effective difference between a falseticker and a server
> > that provides "bad time"?
> 
> See above.
> 
> >
> > - Is this difference really significant?
> 
> See above.
> 
> >
> > - If so, how can ntpd determine the difference between a falseticker and
> > a server that provides "bad time"?
> 
> It cannot easily. All it can do is decide that something is a falseticker. Bu
> t
> noone should think, or say, that that means that the falseticker is a
> bad time source. It may be the best that ntpd can do. That does not mean
> that problems cannot arise precisely because of that. 
> One could for example simply use all the time sources and use them all.
> That has advantages and (as you will be the first to point out)
> disadvantages. 
> 
> Or you could decide that your own clock is a reasonable flywheel, and
> test the outside clocks over time against your won. If you find you own,
> while it freewheels, roughly tracks one of the timesources, you have
> additional evidence that the one may well be ticking at the right rate. 
> Yes, this both requires long term memory, and can certainly at times
> lead you astray. I am sure I could think of other possibilities as well.
> 
> 
> 
> >
> > - what real benefits does one get from knowing the difference?
> 
> Clarity in what one is talking about. Care in setting up one's system.
> knowledge of what the problems can be. 
> 
> Since the purpose of ntpd is to have your computer track the correct
> time ( not the majority time) as closely as possible, realising that
> there may be difference makes you think differently while developing a
> system. What are the costs and benefits of the various possible ways of
> trying to disentable the correct time from the various reports delivered
> by the servers. 
> 
> Maybe majority vote is the best way, but it is certainly not the only
> way or even the ideal way in all circumstances.
> 
> I for one would trust time from a gps pps a lot lot more than that from
> even 3 other servers. And yes, I could be fooled. Just as you might
> trust advice from David Mills much more than any 5 other posters here (
> and would probably be very resistant to a "majority vote" determination
> that David is a "falseticker") but that does not give a guarentee that
> you could not be led astray sometime. 
> 
> 
> >
> > I'm sure a few more questions can come up, but I'm more interested in
> > seeing if there might be something useful going on here, other than
> > coming up with more issues that NTF's nascent Certification and
> > Compliance programs should watch for.
> 
> _______________________________________________
> questions mailing list
> questions at lists.ntp.org
> http://lists.ntp.org/listinfo/questions
> 


More information about the questions mailing list