[ntp:questions] Query about NTP accuracy

Hal Murray hal-usenet at ip-64-139-1-69.sjc.megapath.net
Fri May 22 17:22:09 UTC 2009

In article <4a15e001$0$18238$da0feed9 at news.zen.co.uk>,
 Andy Yates <andyy1234 at gmail.com> writes:
>Does anybody have any figures that shows the effect on accuracy of an
>NTP v3 client using a stratum 1 server rather than a stratum 2 or 3
>server? It's all in a GE LAN based scenario, commercial stratum 1
>servers connected to GPS and stratum 2 and 3 servers are typically
>dedicated Linux boxes.

>However I'm been pressed to supply an SLA for accuracy. My argument is
>that although you can get your stratum one server to synchronize to
>microseconds of UTP, as soon as the client uses NTP v3 over the LAN,
>even a GE LAN, then the accuracy degrades and putting well designed well
>specified stratum between the boxes is not going to decrease accuracy
>sufficiently to warrant purchasing many stratum one appliances.

What sort of accuracy are you interested in?  1 ms?  10 ms?  100 ms?

How stable is your temperature?  (Both the room and the CPU load.)

What is the load on the LAN between the clients and servers?
(Delay is not a problem.  Variation in delay is a problem.)

I suggest you measure it.  Start with your current system.

Setup a box as a ntpd system and tell it to use several target boxes
as servers and turn on logging.  peerstats will tell you the difference
between your local clock and the target system.

These are my opinions, not necessarily my employer's.  I hate spam.

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