[ntp:questions] NTP jitter very large

stephan at newace.ca stephan at newace.ca
Fri Jun 6 12:36:43 UTC 2008


I have a very strange problem that started a few days ago. The server
is running kernel 2.4.28 and has been running for several years
without any issues.

When starting the ntp service, the time is initially set correctly
using ntpdate but after a while, the time will be offset by several
hours. The longer ntp is allowed to run, the larger the offset appears
to be. It seems to level off around 6 hours offset.

When I start NTP and query it at several minute intervals, this is the
result:

After initial startup:
[root at hydra src]# ntpq -p
     remote           refid      st t when poll reach   delay
offset  jitter
==============================================================================
 LOCAL(0)        .LOCL.          13 l    -   64    1    0.000
0.000   0.001
 pbx.... .              INIT.          16 u    -   64    0    0.000
0.000   0.001

After 30 seconds:
     remote           refid      st t when poll reach   delay
offset  jitter
==============================================================================
 LOCAL(0)        .LOCL.          13 l   24   64    1    0.000
0.000   0.001
 pbx....           time-a.nist.gov  2 u   23   64    1    0.214
-702.33   0.001

After 1 minute:
     remote           refid      st t when poll reach   delay
offset  jitter
==============================================================================
 LOCAL(0)        .LOCL.          13 l    2   64    3    0.000
0.000   0.001
 pbx....             time-a.nist.gov  2 u    -   64    3    0.157
-20590. 19888.0


This problem occurs whether I initially sync to an internal server or
NIST directly. The jitter always seems to become very large in a short
period of time.

I upgraded from 4.2.0 to 4.2.4b4, but the problem remains. The
interesting thing to note is that our "pbx" server does not display
this large jitter and is connected to the same network.

Does anyone have any suggestions as to why this would be?

Any assistance would be greatly appreciated.

Regards,

Stephan.




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