[ntp:questions] selection between ntp server and reference clock

Nikolai Orekhov nowhere at mail.ru
Mon Aug 19 09:29:26 UTC 2013


According to http://www.eecis.udel.edu/~mills/ntp/html/prefer.html when
selecting new system peer on the final stage the following happens:

"...The survivor list is then sorted by increasing root distance and the
first entry temporarily designated the system peer. ..."

Imagine there's ntp server and reference clock. Reference clock always has
root distance equal to zero, so it will always be prefered to ntp ( unless
ntp has "prefer" keyword )

So, reference clock could have any dispersion less then 16000 to be
selected. For example, imagine that GPS receiver just appeared from
nowhere, has only one element in filter and dispersion of about 7900. So
for me it's a very bad clock which properties are almost unknown to us.

According to the algorithm such clock would be preferred to any ntpd
server. Please, could someone explain why this was implemented in this way?

May be it will be wiser to make a selection based on dispersion, not a
"root distance" ?

Thanks, Nickolay

More information about the questions mailing list