Time sync with google ntp servers unreliable?

[Rob Gries]

Hello All,

I'm working with an embedded Linux distribution that uses the Google public NTP servers to synchronize date/time, and I am having some issues when using systemd-timesyncd to synchronize with time[1-4].google.com.

Looking at the logs below it looks like that it eventually succeeds with one or more of the public NTP servers, but it seems to time out most of the time. Is this normal?

root@dragonboard410c:~# journalctl -u systemd-timesyncd -f
-- Logs begin at Thu 1970-01-01 00:00:02 UTC. --
Jan 01 00:00:04 dragonboard410c systemd[1]: Starting Network Time Synchronization...
Jan 01 00:00:04 dragonboard410c systemd-timesyncd[2773]: System clock time unset or jumped backwards, restoring from recorded timestamp: Tue 2018-06-05 14:54:23 UTC
Jun 05 14:54:23 dragonboard410c systemd[1]: Started Network Time Synchronization.
Jun 05 14:54:28 dragonboard410c systemd-timesyncd[2773]: Network configuration changed, trying to establish connection.
Jun 05 14:55:08 dragonboard410c systemd-timesyncd[2773]: Timed out waiting for reply from 216.239.35.8:123 (time3.google.com).
Jun 05 14:55:19 dragonboard410c systemd-timesyncd[2773]: Timed out waiting for reply from 216.239.35.12:123 (time4.google.com).
Jun 05 14:56:01 dragonboard410c systemd-timesyncd[2773]: Timed out waiting for reply from 216.239.35.0:123 (time1.google.com).
Jun 05 14:56:11 dragonboard410c systemd-timesyncd[2773]: Timed out waiting for reply from 216.239.35.4:123 (time2.google.com).
Jun 05 14:56:22 dragonboard410c systemd-timesyncd[2773]: Timed out waiting for reply from 216.239.35.8:123 (time3.google.com).
Jun 05 15:10:18 dragonboard410c systemd-timesyncd[2773]: Synchronized to time server 216.239.35.12:123 (time4.google.com). --- Eventually succeeds...
Jun 05 15:12:37 dragonboard410c systemd-timesyncd[2773]: Timed out waiting for reply from 216.239.35.12:123 (time4.google.com).
Jun 05 15:13:19 dragonboard410c systemd-timesyncd[2773]: Timed out waiting for reply from 216.239.35.0:123 (time1.google.com).
Jun 05 15:13:29 dragonboard410c systemd-timesyncd[2773]: Timed out waiting for reply from 216.239.35.4:123 (time2.google.com).
Jun 05 15:13:40 dragonboard410c systemd-timesyncd[2773]: Timed out waiting for reply from 216.239.35.8:123 (time3.google.com).
Jun 05 15:13:50 dragonboard410c systemd-timesyncd[2773]: Timed out waiting for reply from 216.239.35.12:123 (time4.google.com).

I only started seeing this today, is there an ongoing administrative event causing this behavior?

Meanwhile, the US NIST time servers seem to respond faster and do not time out.

root@dragonboard410c:~# journalctl -u systemd-timesyncd.service -f
-- Logs begin at Thu 1970-01-01 00:00:02 UTC. --
Jan 01 00:26:07 dragonboard410c systemd-timesyncd[4672]: Timed out waiting for reply from 216.239.35.4:123 (time2.google.com).
Jan 01 00:26:17 dragonboard410c systemd-timesyncd[4672]: Timed out waiting for reply from 216.239.35.8:123 (time3.google.com).
Jan 01 00:26:27 dragonboard410c systemd-timesyncd[4672]: Timed out waiting for reply from 216.239.35.12:123 (time4.google.com).
Jan 01 00:34:04 dragonboard410c systemd[1]: Stopping Network Time Synchronization...
Jan 01 00:34:04 dragonboard410c systemd[1]: Stopped Network Time Synchronization.
Jan 01 00:34:04 dragonboard410c systemd[1]: Starting Network Time Synchronization...
Jan 01 00:34:04 dragonboard410c systemd[1]: Started Network Time Synchronization.
Jun 05 14:26:44 dragonboard410c systemd-timesyncd[6502]: Synchronized to time server 129.6.15.28:123 (time-a.nist.gov).
Jun 05 14:39:58 dragonboard410c systemd-timesyncd[6502]: Network configuration changed, trying to establish connection.
Jun 05 14:42:07 dragonboard410c systemd-timesyncd[6502]: Synchronized to time server 129.6.15.28:123 (time-a.nist.gov).

Seeing that I can use the NIST ntp server without failure, it seems that this issue is not a local network configuration issue, as both the NIST NTP servers and the Google public NTP servers are using the same port/protocol.

[Chris Schrier]

Hello,

Our probers have not identified any major communication issues; there was a ~2% failure ratio 2018-06-04 20:56 - 21:23 PDT but it has been insignificant otherwise. What RTT do you have to each VIP according to ping? It is incredibly odd that NIST is working while Google's Public NTP service is not.

Can you provide that output of `ntpdate -qdv time1.google.com` as well? 

I will note that it's generally not advisable to mix servers that smear leap seconds and those that do not, you may experience unpredictable behavior.

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