[ntp:questions] NTP-Question about "ntpq -p"

Unruh unruh-spam at physics.ubc.ca
Fri Aug 29 05:38:42 UTC 2008

manuel.beicht at gmx.de (Manuel Beicht) writes:


>I have some questions regarding synchronization and the output of "ntpq -p".
>For example what is the significance of the "*" for example when you run ntpq
>-p. Is this star a must because I have seen the polling sometimes and the time
>mostly accurate but the "*" is missing. So does the server have to have a "*"
>to be synched?  In ntp documentation I read it just means that "*" denotes the
>server that the NTP client is synching to but not necessarily that they are IN
>synch. I am asking so far I considered any server without a "*" out of synch.

Yes, * means it is the selected source. that ntp will slowly try to sync

>Then I noticed the polling is dynamic but it seems to be too long with some
>intervals and in particular too long when there is an offset. For example if
>we have an offset of 1000 the polling is at 128 or at 256 instead of 64 or a

If you have an offset of 1000 ntp will carry out a step when it decides
that that is a genuine (ie, that the minimum offset recorded during 8
polling intervals) offset. 
If you have an offset of 1000 something is very wrong with your network
connection or your system.

>lower level which I think would be more logical. There are actually some posts
>on the ntp support sites that mention using custom polling parameters based on
>the offset and latency ect...that do polling at 10 min 15 max and there is
>some type of algorithm to find a match for anyone site.

It is slow to decrease the poll interval. 

>Also what is acceptable offset and jitter? We currently experience 20-40ms
>offset and 20-30ms jitter. sometimes it is up to 100-120ms offset.

That is unusual. What kind of network connection do you have? A telephone
modem connection? For a high speed connection, the usual offset is in the
10s of microsecond range for a local server, and 100s of microseconds for a
relatively local machine. Even half way across the continent with a delay
of 45ms, the offset is 100s of microseconds. 


>Is that still ok? What is the acceptable range usually?

>I would be very glad if you could provide me with some help.



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