[ntp:questions] "ntpd[7602]: synchronized to"

Chuck Swiger cswiger at mac.com
Thu May 26 16:49:55 UTC 2011


On May 26, 2011, at 9:28 AM, Florin Andrei wrote:
> On 05/23/2011 03:57 PM, Chuck Swiger wrote:
>> 
>> That being said, it's not expected that the preferred time source would change that frequently.  You'd probably do better to run with at least 4 servers, so that it can better judge their reliability; with only two, there isn't much basis for comparison.
> 
> So, basically you're saying the "quality" of the NTP servers fluctuates for some reason and this machine is flipping back and forth between them?

Evidently yes for your case.  With only two servers, it may not be possible to find a best intersection via ntpd's variant of Marzullo's algorithm:

  http://en.wikipedia.org/wiki/Marzullo%27s_algorithm

> Hmm... Both NTP servers are on the same LAN, same hardware and OS like the client machine, are synced to public pools, and peered with other NTP local servers, both on the same LAN and over a WAN. They seem fine to me.
> 
> ###########################################
> server 0.us.pool.ntp.org iburst
> server 1.us.pool.ntp.org iburst
> server 2.us.pool.ntp.org iburst
> server 3.us.pool.ntp.org iburst
> 
> restrict 0.us.pool.ntp.org mask 255.255.255.255 nomodify notrap noquery
> restrict 1.us.pool.ntp.org mask 255.255.255.255 nomodify notrap noquery
> restrict 2.us.pool.ntp.org mask 255.255.255.255 nomodify notrap noquery
> restrict 3.us.pool.ntp.org mask 255.255.255.255 nomodify notrap noquery

I believe your ntpd version is too old for this to work as you might expect.  0.us.pool.ntp.org isn't one A record in the DNS; it's many, and which IP is chosen in the server line might not match the IP chosen for the restrict line.  In other words, "restrict ignore" is probably in affect for some of the servers being listed.

See:

  http://support.ntp.org/bin/view/Support/AccessRestrictions

...or check your "ntpq -p" scoreboard.

Regards,
-- 
-Chuck




More information about the questions mailing list