[ntp:questions] peers using same server

Miroslav Lichvar mlichvar at redhat.com
Mon Nov 1 13:13:41 UTC 2010


I've come across an interesting problem and I'm not sure if this is a
bug or feature.

When two peers are configured to use the same server as their source
and the link between one peer and the server goes down, the peer
doesn't switch to the other peer and will stay unsynchronized.

 1 Jan 01:00:00 ntpd[3468]: ntpd 4.2.7p71 at 1.2297 Mon Oct 25 09:43:53 UTC 2010 (1)
 1 Jan 01:00:00 ntpd[3468]: proto: precision = 0.101 usec
 1 Jan 01:00:00 ntpd[3468]: ntp_io: estimated max descriptors: 1024, initial socket boundary: 16
 1 Jan 01:00:00 ntpd[3468]: Listen and drop on 0 v4wildcard 0.0.0.0 UDP 123
 1 Jan 01:00:00 ntpd[3468]: Listen normally on 1 lo 127.0.0.1 UDP 123
 1 Jan 01:00:00 ntpd[3468]: Listen normally on 2 eth0 192.168.123.4 UDP 123
 1 Jan 01:00:00 ntpd[3468]: 192.168.123.1 8011 81 mobilize assoc 9201
 1 Jan 01:00:00 ntpd[3468]: 192.168.123.3 8011 81 mobilize assoc 9202
 1 Jan 01:00:00 ntpd[3468]: 0.0.0.0 c016 06 restart
 1 Jan 01:00:00 ntpd[3468]: 0.0.0.0 c012 02 freq_set kernel 100.000 PPM
 1 Jan 01:05:29 ntpd[3468]: 192.168.123.3 8024 84 reachable
 1 Jan 01:08:44 ntpd[3468]: 192.168.123.3 963a 8a sys_peer
 1 Jan 01:08:44 ntpd[3468]: 0.0.0.0 c615 05 clock_sync
 1 Jan 19:11:37 ntpd[3468]: 192.168.123.1 8024 84 reachable
 1 Jan 19:40:48 ntpd[3468]: 192.168.123.1 963a 8a sys_peer
 1 Jan 22:03:04 ntpd[3468]: 192.168.123.1 8643 83 unreachable
 1 Jan 22:07:08 ntpd[3468]: 0.0.0.0 0618 08 no_sys_peer
 2 Jan 16:07:01 ntpd[3468]: 192.168.123.1 8054 84 reachable
 2 Jan 16:12:32 ntpd[3468]: 192.168.123.1 966a 8a sys_peer
 2 Jan 18:58:12 ntpd[3468]: 192.168.123.1 8673 83 unreachable
 2 Jan 19:00:34 ntpd[3468]: 0.0.0.0 0628 08 no_sys_peer

But when each peer uses a different server, they will switch to the
other peer quickly when the link goes down.

 1 Jan 01:00:00 ntpd[3635]: ntpd 4.2.7p71 at 1.2297 Mon Oct 25 09:43:53 UTC 2010 (1)
 1 Jan 01:00:00 ntpd[3635]: proto: precision = 0.101 usec
 1 Jan 01:00:00 ntpd[3635]: ntp_io: estimated max descriptors: 1024, initial socket boundary: 16
 1 Jan 01:00:00 ntpd[3635]: Listen and drop on 0 v4wildcard 0.0.0.0 UDP 123
 1 Jan 01:00:00 ntpd[3635]: Listen normally on 1 lo 127.0.0.1 UDP 123
 1 Jan 01:00:00 ntpd[3635]: Listen normally on 2 eth0 192.168.123.4 UDP 123
 1 Jan 01:00:00 ntpd[3635]: 192.168.123.2 8011 81 mobilize assoc 9201
 1 Jan 01:00:00 ntpd[3635]: 192.168.123.3 8011 81 mobilize assoc 9202
 1 Jan 01:00:00 ntpd[3635]: 0.0.0.0 c016 06 restart
 1 Jan 01:00:00 ntpd[3635]: 0.0.0.0 c012 02 freq_set kernel 100.000 PPM
 1 Jan 01:05:29 ntpd[3635]: 192.168.123.3 8024 84 reachable
 1 Jan 01:09:54 ntpd[3635]: 192.168.123.3 963a 8a sys_peer
 1 Jan 01:09:54 ntpd[3635]: 0.0.0.0 c615 05 clock_sync
 1 Jan 02:49:28 ntpd[3635]: 192.168.123.2 8024 84 reachable
 1 Jan 03:11:52 ntpd[3635]: 192.168.123.2 963a 8a sys_peer
 1 Jan 05:40:36 ntpd[3635]: 192.168.123.2 8643 83 unreachable
 1 Jan 05:48:17 ntpd[3635]: 192.168.123.3 961a 8a sys_peer
 1 Jan 07:22:11 ntpd[3635]: 192.168.123.2 8054 84 reachable
 1 Jan 08:01:28 ntpd[3635]: 192.168.123.2 966a 8a sys_peer
 1 Jan 10:13:37 ntpd[3635]: 192.168.123.2 8673 83 unreachable
 1 Jan 10:20:08 ntpd[3635]: 192.168.123.3 961a 8a sys_peer

Any explanation for this? I've tried versions 4.2.2, 4.2.4, 4.2.6 and
the latest dev, the result is always the same.

Thanks,

-- 
Miroslav Lichvar



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