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

Joseph Gwinn joegwinn at comcast.net
Fri Mar 13 04:31:11 UTC 2009


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.

Although most received replies have status 9514, they are nonetheless 
used to update the loop filter and so appear in the loopstats file.  
When I co-plot loopstats and peerstats, the loopstats dots land on top 
of the peerstats dots.

What is this error likely telling me?  What are the possibilities?  What 
tests will tell the tale?

Thanks to all,

Joe Gwinn




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