[ntp:questions] Is this normal behavior?

Zembower, Kevin kzembowe at jhuccp.org
Fri Dec 8 15:39:11 UTC 2006


I'm not very knowledgeable about NTP, but I'm suspicious of its
implementation on one of my servers. I have one server running the
Debian sarge package of NTP:
cn2:/var/log# ntpq
ntpq> version
ntpq 4.2.0a at 1:4.2.0a+stable-2-r Fri Aug 26 10:30:19 UTC 2005 (1)
ntpq>

I've tried to set this server up as a timeserver for my network, using
tock.usno.mil, a time server at my institution (Johns Hopkins
University) and the pool timeservers:
ntpq> peers
     remote           refid      st t when poll reach   delay   offset
jitter
========================================================================
======
+jhname.hcf.jhu. 128.4.1.1        2 u   60   64  177    3.313  835.818
545.232
*ntp1.usno.navy. .USNO.           1 u   60   64  177    8.567  827.174
551.616
+trane.wu-wien.a 195.13.1.153     3 u   57   64  177  125.292  841.188
548.251
+221-15-178-69.g 140.142.16.34    2 u   50   64  177  107.300  1212.00
395.490
+tock.jrc.us     207.168.62.76    2 u   58   64  177   16.942  1020.49
432.251
 LOCAL(0)        LOCAL(0)        13 l   55   64  177    0.000    0.000
0.002
ntpq>

I notice the problem here, and if I run 'watch ntpq -p.' Seldom is my
reachability 377, and it frequently and inexplicitly drops to 1 as I'm
watching it. Ten minutes ago reachability was 177 as shown above.
Watching it in the last minute, it dropped from 377 to 1 on all sources.
Now it's:
Every 2s: ntpq -p
Fri Dec  8 10:35:18 2006

     remote           refid      st t when poll reach   delay   offset
jitter
========================================================================
======
 jhname.hcf.jhu. 128.4.1.1        2 u   53   64    3    2.707  660.049
176.587
 ntp1.usno.navy. .USNO.           1 u   52   64    3    8.904  663.193
181.873
 trane.wu-wien.a 195.13.1.153     3 u   49   64    3  125.979  681.070
186.182
 221-15-178-69.g 140.142.16.34    2 u   51   64    3  104.207  485.281
183.834
 tock.jrc.us     207.168.62.76    2 u   50   64    3   16.912  668.565
186.520
 LOCAL(0)        LOCAL(0)        13 l   49   64    3    0.000    0.000
0.002

Is this normal behavior for NTP, to frequently lose the ability to reach
a timeserver? If not, how can I troubleshoot it further?

Here's the syslog entries pertaining to npt for just one hour this
morning:
Dec  8 09:03:06 cn2 ntpd[16955]: time reset +3.120367 s
Dec  8 09:07:21 cn2 ntpd[16955]: synchronized to LOCAL(0), stratum 13
Dec  8 09:08:25 cn2 ntpd[16955]: synchronized to 67.128.71.75, stratum 2
Dec  8 09:09:31 cn2 ntpd[16955]: synchronized to 192.5.41.41, stratum 1
Dec  8 09:23:33 cn2 ntpd[16955]: time reset +3.503628 s
Dec  8 09:27:51 cn2 ntpd[16955]: synchronized to LOCAL(0), stratum 13
Dec  8 09:28:56 cn2 ntpd[16955]: synchronized to 192.5.41.41, stratum 1
Dec  8 09:36:18 cn2 ntpd[16955]: synchronized to 128.220.2.7, stratum 2
Dec  8 09:36:25 cn2 ntpd[16955]: synchronized to 192.5.41.41, stratum 1
Dec  8 09:40:40 cn2 ntpd[16955]: synchronized to 128.220.2.7, stratum 2
Dec  8 09:41:45 cn2 ntpd[16955]: synchronized to 192.5.41.41, stratum 1
Dec  8 09:41:47 cn2 ntpd[16955]: synchronized to 69.178.15.221, stratum
2
Dec  8 09:43:46 cn2 ntpd[16955]: synchronized to 192.5.41.41, stratum 1
Dec  8 09:49:21 cn2 ntpd[16955]: synchronized to 67.128.71.75, stratum 2
Dec  8 09:49:21 cn2 ntpd[16955]: time reset +4.512453 s
Dec  8 09:53:41 cn2 ntpd[16955]: synchronized to LOCAL(0), stratum 13
Dec  8 09:54:39 cn2 ntpd[16955]: synchronized to 128.220.2.7, stratum 2
Dec  8 09:54:44 cn2 ntpd[16955]: synchronized to 192.5.41.41, stratum 1
Dec  8 10:01:11 cn2 ntpd[16955]: synchronized to 67.128.71.75, stratum 2
Dec  8 10:02:14 cn2 ntpd[16955]: synchronized to 192.5.41.41, stratum 1
Dec  8 10:09:40 cn2 ntpd[16955]: synchronized to 67.128.71.75, stratum 2
Dec  8 10:10:51 cn2 ntpd[16955]: synchronized to 192.5.41.41, stratum 1
Dec  8 10:10:51 cn2 ntpd[16955]: time reset +3.950081 s
Dec  8 10:15:08 cn2 ntpd[16955]: synchronized to LOCAL(0), stratum 13
Dec  8 10:16:14 cn2 ntpd[16955]: synchronized to 192.5.41.41, stratum 1

These time resets seem rather large to me. Is this normal, too?

Here's the output of the peerstat.qwk script:
cn2:/var/log/ntpstats# gawk -f
/home/kevinz/ntp-4.2.2p4/scripts/stats/peer.awk peerstats
       ident     cnt     mean     rms      max     delay     dist
disp
========================================================================
==
67.128.71.75     715 2364.263  996.393 2364.263   16.751  947.994
96.315
127.127.1.0      844    0.000    0.000    0.000    0.000    0.990
0.957
192.5.41.41      728 2321.937 1023.300 2964.896    7.907  944.371
94.581
137.208.3.51     675 2500.134  995.134 3013.699  124.989  503.205
44.951
128.220.2.7      721 2405.904  982.298 2712.599    2.564  940.869
95.476
69.178.15.221    722 2395.872 1002.130 2911.691  104.730  997.703
95.423
cn2:/var/log/ntpstats#

Are there any other diagnostics that I could run to help identify any
problem?

Thank you all for your help, advice and suggestions.

-Kevin

Kevin Zembower
Internet Services Group manager
Center for Communication Programs
Bloomberg School of Public Health
Johns Hopkins University
111 Market Place, Suite 310
Baltimore, Maryland  21202
410-659-6139 



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