[ntp:questions] Output of ntpq -p regarding stratum level

Nottorf, Stefan Stefan.Nottorf at plath.de
Tue Sep 9 13:54:20 UTC 2008


Hello,
although this is probably a beginner's question, I would like to
understand this before I run into trouble caused by misunderstanding
basic information. I think i misunderstood how to read the output of
ntpq -p... 
The third column ("st") shows the stratum.
But beginning to monitor time synchronization in our network, I noticed
a slight difference in the understanding of stratum levels between me
and the monitoring tool (Nagios).
When I use ntpq -p on one of our hosts I get the following output:

remote      refid   st t when poll reach delay offset   jitter
========================================================================
======
*10.x.y.z   .PPS.    1 u  338 1024  377  0.454 -1.559   0.078
name1.name  10.x.y.z 2 u  471 1024  376  0.209  1.763   0.093
name2.name  10.x.y.z 2 u 1461 1024  374  0.001  2.652   0.206
name3.name  10.x.y.z 2 u  596 1024  376  0.385  0.052   0.322
LOCAL(0)    .LOCL.   5 l   59   64  377  0.000  0.000   0.001

Until now I read this line :*10.x.y.z   .PPS.    1 u  338 1024  377
0.454 -1.559   0.078
the following way:
The host I ran ntpq -p on is synchronized to (*) server 10.x.y.z., whose
time source is a PulsePerSecond clock. 10.x.y.z is a server at stratum 1
and 338 seconds have passed since the last poll. The poll interval is
1024 seconds.
Because the time reference is located at stratum 1, this host is located
at stratum 2.
Similarily, if I look at server name1.name: name1.name is a server
located at stratum 2 and is itself synchronized to server 10.x.y.z.
If this is correct so far, the following output confuses me. I ran a
check for time synchronization for Nagios. Nagios provides a couple of
checks, one of them called check_ntp_peer. I use it to detect
differences between expected and current stratum levels.

/<installation_path>/libexec/check_ntp_peer -H name1.name -W 4 -C 6 -v

1 candiate peers available
synchronization source found
Getting offset, jitter and stratum for peer 4551
parsing offset from peer 4551: -0.001193
parsing stratum from peer 4551: 1
NTP OK: Offset -0.001193 secs,
stratum=1|offset=-0.001193s;60.000000;120.000000; stratum=1;4;6;0;16

This output tells me, that name1.name is located in stratum 1 (instead
of the expected stratum 2). 

In short: does the column st refer to the stratum of the remote host OR
does it mean "If I synchronize to that remote host I will get to stratum
x" ?
Thanks and regards,
Stefan Nottorf




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