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

Richard B. Gilbert rgilbert88 at comcast.net
Sat Mar 14 02:54:17 UTC 2009


Joseph Gwinn wrote:
> I have been debugging some system problems.  The main system is too 
> complicated, with too many people doing too many things, so I sought 
> quiet refuge in an isolated test system consisting of a NTP timeserver 
> connected by a point-to-point ethernet cable to a computer running NTP, 
> which generates peerstats and loopstats data.  This test system is 
> air-gap isolated from the rest of everything.  Only one timeserver is 
> available to a given computer at a time.
> 
> 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.
> 
> The computer can be a Sun Ultra 10 or a Sun Ultra 60, in both cases 
> running Solaris 9.  Solid boxes, but old.  The OS version reply is SunOS 
> 5.9 Generic May 2002.  This was clean installed from CD a week ago, so 
> has not had time to collect too many barnicles.
> 
> NTP version 3 is running.  I've been trying to find the command to give 
> me the full version, including dot (like 3.4y), and I get answers, but 
> don't know which one to believe, and if the version given is that of the 
> NTP daemon itself, or of ntpq, or of ntpdate.
> 
> The full grid of four tests, being two timeservers by two computers, has 
> been run.  Many odd things are seen, but the question for today is about 
> status codes in peerstats file records.
> 
> 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.
> 
I think that, perhaps, "maximum distance" refers to "synchronization 
distance" q.v.  Once upon a time, I knew the definition but my memory 
has failed me.




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