[ntp:questions] NTP Clock Hopping Question

Ouk Ouk at netscape.net
Tue Sep 23 17:25:05 UTC 2003


Hi,

I've an OpenVMS system (OpenVMS 7.3, TCPIP Services 5.1 implementing
NTP V3) that I want to synchronise to a collection of corporate
Stratum-2 NTP time servers.

I've the following server/peer entries in my configuration file:

server 10.3.1.11
server 10.1.1.11
server 10.4.1.11
server 10.3.2.11
peer NODE2


The results of an NTPQ are:

$ ntpq -p

     remote           refid      st t when poll reach   delay   offset
   disp
==============================================================================
+10.3.1.11       10.1.3.4         2 u   63   64  377     0.89    1.081
   0.70
-10.1.1.11       10.2.1.2         2 u    6   64  377     0.87   -0.520
   0.90
+10.4.1.11       10.1.3.4         2 u   18   64  377     8.79    0.796
   1.37
*10.3.2.11       10.2.1.2         2 u   14   64  377     0.00   -0.379
   1.33
 LOCAL(0)        LOCAL(0)        10 l   39   64  377     0.00    0.000
  10.48
+NODE2           10.1.3.2         3 u   40   64  376    -0.27   -1.071
   1.79


NODE2 is another OpenVMS Alpha with a similar set-up although it looks
at a different set of four Stratum-2 servers. The fudged local clock
is there for other nodes in the local LAN to use once I've stabilised
this set-up.

I'm seeing (I believe) an excessive amount of clock hopping (every 2-3
minutes or so) between the NTP servers. For example, in the last hour:

23 Sep 16:53:17  synchronized to 10.1.1.11, stratum=2
23 Sep 16:53:43  synchronized to 10.3.2.11, stratum=2
23 Sep 16:57:54  synchronized to 10.1.1.11, stratum=2
23 Sep 16:58:00  synchronized to 10.3.2.11, stratum=2
23 Sep 17:05:01  synchronized to 10.1.1.11, stratum=2
23 Sep 17:11:36  synchronized to 10.3.2.11, stratum=2
23 Sep 17:19:59  synchronized to 10.1.1.11, stratum=2
23 Sep 17:21:44  Previous time adjustment incomplete; residual
0.000001 sec
23 Sep 17:21:51  synchronized to 10.3.2.11, stratum=2
23 Sep 17:24:39  synchronized to 10.1.1.11, stratum=2
23 Sep 17:24:56  synchronized to 10.3.2.11, stratum=2
23 Sep 17:27:53  synchronized to 10.1.1.11, stratum=2
23 Sep 17:35:13  synchronized to 10.3.2.11, stratum=2
23 Sep 17:37:10  synchronized to 10.1.1.11, stratum=2
23 Sep 17:41:09  offset: 0.000426 sec  freq: 1.850 ppm  poll: 64 sec
23 Sep 17:44:52  synchronized to 10.3.1.11, stratum=2
23 Sep 17:45:47  synchronized to 10.3.2.11, stratum=2
23 Sep 17:46:00  synchronized to 10.1.1.11, stratum=2
23 Sep 17:47:38  synchronized to 10.3.2.11, stratum=2
23 Sep 17:47:44  synchronized to 10.4.1.11, stratum=2
23 Sep 17:52:44  synchronized to 10.3.2.11, stratum=2
23 Sep 17:52:59  synchronized to 10.1.1.11, stratum=2

I think the clock-hopping may be a result of the corporate server
set-up, which is not under my control - The 'refid' of the Stratum-2
servers appears to change quite frequently.

I'm thinking of adding a 'prefer' keyword to one of the server
configuration lines in order to stop this - is this a good idea? Or,
have I made some awful configuration faux-pas that's causing these
results?

Ouk.



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