[ntp:questions] Server offset included in served time?

Steve Kostecke kostecke at ntp.org
Fri Sep 12 23:03:22 UTC 2008

On 2008-09-12, David Woolley <david at ex.djwhome.demon.co.uk.invalid> wrote:
> Howard Barina wrote:
>> Does an NTP servers take into account it's estimated offset in serving time
>> to others?  If I am a server and think I am 1.5 milliseconds off from true
>> time, will I include this in the timestamps of my ntp replies to others?
> An NTP client never thinks that its time is wrong.  If it did, it would 
> be admitting that the NTP algorithms are wrong.  Therefore the server 
> always serves its client's idea of the time.
> The "offset" should always be within the statistical error from the 
> current measurement history (if ntpd suspects otherwise, it steps, 
> and/or reduces the poll interval, to try to rapidly re-acquire that 
> condition).  Immediately after startup, there will be little history, so 
> quite large offsets will still be consistent with that history.

A single snapshot value is of limited value because values such as the
offset are contantly changing. The long term stability of the clock is
more important than a single snapshot.

peer.awk from the ./scripts directory in the Distribution is good tool
for summarizing peerstats files.

Steve Kostecke <kostecke at ntp.org>
NTP Public Services Project - http://support.ntp.org/

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