[ntp:questions] confusing clock selection...

Florian Heigl florian.heigl at gmail.com
Fri Jul 8 14:43:43 UTC 2011


I'm doing some testing of the ntp config I made and don't really
understand what just happened.
Primarly I'm looking at two ntp servers and one clock out of a larger
NTP is quite critical so I've already done some head-scratching to
come to this setup.

Setup on "ntp01":
server meinberg1
server meinberg2 prefer
server meinberg3
server meinberg4
peer ntp02 iburst # this line reads ntp01 on the other server

# local fallback clock
fudge stratum 10

driftfile /var/lib/ntp/drift

Note about the local clock: Like with the "real" Meinberg clocks I
want clients to keep syncing to ntp01/ntp02 even if all upstream
sources are gone.

Right now only Meinberg3 is online, and, to make things more
interesting, I unplugged it's GPS cable. It kept going at stratum 1/2
for a long duration and now went down to stratum 3 local source.

I would have hoped both "ntp" servers would still use meinberg3,
instead they decided to pick their local clock.

     remote           refid      st t when poll reach   delay
offset  jitter
 meinberg1          .INIT.          16 u    -   64    0    0.000
0.000   0.000
 meinberg2          .INIT.          16 u    -   64    0    0.000
0.000   0.000
 meinberg3          LOCAL(0)         3 u   34   64    7    0.192
-1531.5   5.156
 meinberg4          .INIT.          16 u    -   64    0    0.000
0.000   0.000
 ntp02        LOCAL(0)        11 u   24   64   17    0.216  -1529.3
*LOCAL(0)        .LOCL.          10 l   30   64   17    0.000
0.000   0.001

As you'll see it picked it's local clock as it's best friend now, same
for ntp02.
I would expect them to pick meinberg3 as active source since it is at
stratum 3, and to also sync with their peer (maybe the problem is
around this?)

NTP Version is one from CentOS 5.

I really do love working with NTP, just right now I don't understand
why it does what it's doing (even if it may just be what I configured
into it, right?

I'm wishing a nice weekend to all of you and would love to hear from
anyone who can help me understand what I got wrong in this config!

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