[ntp:questions] Re: Server Sync Problem

Richard B. Gilbert rgilbert88 at comcast.net
Sat Dec 17 14:37:31 UTC 2005

Michael wrote:

>I have a real headache of a problem with NTP and clients failing to sync 
>with the server, so any
>help will be greatly appreciated.
>I have a Linux solid state GPS based NTP server running NTP 4.2.......
>It is rock steady. Server time offset is always < 1ms, usually much less and 
>jitter is usually less than .01 ms.
>I have many other Linux servers running Gentoo and NTP 4.2.....
>3) Problem 1
>If I tell these servers to sync directly to the GPS server as clients, they 
>do suceed, but then
>they lose sync for a few minutes and then find it again etc etc. NTP reports 
>in /var/log/messages
>that "No servers reachable", but I have sat there with tcpdump running 
>watching the UDP
>request/responses ticking away with no problems whatsoever. No packets are 
>lost at all.
>But NTP just doesnt seem to like whats going on.
>However, if I make the client "burst" to the server, it never seems to lose 
>sync at all. Why I need
>to use burst on a LAN when I cant see any packet loss, I dont know but it 
>seems to fix the problem.
>4) Problem 2
>Now, if I sync a server lets call it A, off the GPS server, then try to sync 
>the other servers off A, none
>of them will sync at all even though NTP can see server A and ntpq reports a 
>reach of 377, the offset is
>< 1ms and the jitter is < .01ms  and tcpdump sees all the UDP 
>request/response packets without any problems.
>So communication with the server appears to be fine, but NTP just doesnt 
>want to sync up at all.
>Anybody got any ideas as to what is happening as I am going slowly mad.
It might be helpful to post copies of your ntp.conf files and the output 
of ntpq -p.
What command did you use to start ntpd; e.g. any options used?

More information about the questions mailing list