[ntp:questions] What exactly does "Maximum Distance Exceded" mean?

Joseph Gwinn joegwinn at comcast.net
Fri Mar 13 15:47:59 UTC 2009


In article 
<8dca286d-ba66-4caf-8090-a3467064a8e9 at s20g2000yqh.googlegroups.com>,
 Mike K Smith <mks-usenet at dsl.pipex.com> wrote:

> On 13 Mar, 04:31, Joseph Gwinn <joegw... at comcast.net> wrote:
> > The timeserver can be either a Symmetricom ET6010 GPS receiver feeding
> > an IRIG-B002 time signal to a Symmetricom TS2100 Network Time Server, or
> > a Spectracom 9383 NTP timeserver with built-in GPS receiver.  The GPS
> > receivers are driven from a common antenna via a splitter.
> I'm familiar with the Spectracom 9383, but not the other equipment.

The Symmetricom units are quite old.


> What does the NTP status page show?
> 
> What does the GPS Signal Status show?
> 
> How many satellites are you seeing?
> 
> Is the device reporting 'Position Hold'?

I'll check.


> > Most of the replies that NTP is using to update the time have a status
> > code of 9514, which translates to the following:
> >
> > Configured, reachability OK; Current sync source - max distance
> > exceeded; Count is 1; Peer now reachable.
> >
> > The part that has me most perplexed is the "max distance exceeded" part,
> > as this is a direct wired connection, with zero hops, zero delay, and no
> > interfering traffic.  Obviously, they are not talking about physical
> > distance or hops or the like, so the "distance" has to have units of
> > time.
> >
> > Although most received replies have status 9514, they are nonetheless
> > used to update the loop filter and so appear in the loopstats file.  
>
> You say most are 9514, are there any 96xx values?

The status codes seen are 9014 (red), 9514 (orange), and 9614 (green).  

The colors are those of the plotted dots.  Loopstats dots are dark blue 
and smaller, so when co-plotted one sees little bullseyes.

I see 9014 when changing cables or timeservers, and in most other tests 
I see mostly 9614 and a few 9014, and very rarely 9514 until now.

 
> > When I co-plot loopstats and peerstats, the loopstats dots land on top
> > of the peerstats dots.
>
> I've never seen a device come up as status 5, but since the RFC1305
> text treats it as "current synchronization source; max distance
> exceeded (if limit check implemented)" then I guess it makes sense
> that it will use it as the sync source and will update loopstats
> appropriately.

I had not seen 5 before either, but NTP is clearly using these replies 
to update the time.


Joe Gwinn




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