[Nagiosplug-devel] check_ntp

[Holger Weiss]

* Thomas Guyot-Sionnest <dermoth at aei.ca> [2007-04-05 09:29]:
> On 05/04/07 03:08 AM, sean finney wrote:
> > On Wed, 2007-04-04 at 18:05 -0400, Thomas Guyot-Sionnest wrote:
> >> Not really. I don't know what's taken into account when calculating the
> >> jitter but the dispersion is definately higher in general (or always?)
> >
> > okay, here are some definitions  i got from an ntp powerpoint
> > presentation made by the author:
> >
> > Jitter: exponential average of first-order time differences
> > Dispersion: maximum error due oscillator frequency tolerance.
> >
> > so yeah, not quite the same thing.  and as you pointed out the
> > differences in value are quite big.  should we really be checking it
> > with jitter then?  maybe instead we could extend the plugin to check
> > various variables/thresholds, and have it return some failure status
> > when a non-existant variable is requested?
>
> That could begin to confuse users that don't know much about NTP.
> Aspecially since "ntpq -p <host>" will return the dispersion if there is
> no jitter. I'd suggest the same behavior for check_ntp.

I agree, precisely for this reason.

> >> What's you're pooling in the jitter section is local variables on the
> >> remote server. That server will update them as time goes, but they'Re
> >> not affected by network conditions.
> >
> > ah, i see.  so the control packet data probably won't change in the
> > interval that it's being checked.  in that case it doesn't make any
> > sense to average it, i agree.  however, since this is udp we're talking
> > about, maybe it's still worthwhile to throw a couple extra packets on
> > the wire to make sure one of them is recieved?  or perhaps we could
> > default to a single packet, but provide a configurable retry parameter
> > or something.
>
> I'll take a look at what the other check used to do... But I doubt it
> would be useful for the jitter section.

Why not?  Retries are a good idea IMO.

Holger

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