[ntp:questions] FreeBSD refclock error

Kevin Oberman oberman at es.net
Tue Aug 14 22:15:07 UTC 2007

> Date: Tue, 14 Aug 2007 14:05:40 -0700
> From: David Newman <dnewman at networktest.com>
> Sender: questions-bounces+oberman=es.net at lists.ntp.org
> Hash: SHA1
> On 8/14/07 5:51 AM, Jason Rabel wrote:
> >> ACK, thanks also for these tips.
> >>
> >> Next newbie question: Is ".GPS." the correct refid I should see?
> >>
> >> lancelot# ntpq -p
> >> remote      refid      st t when poll reach   delay   offset jitter
> >> =====================================================================
> >> *time.domain.tld .GPS.  1 u   33   64  377    0.746  -40.803 20.547
> >>
> > 
> > The 'refid', in this case 'GPS' is the source which time.domain.tld is
> > synced to. If it was synced to another NTP server then it would list its IP
> > there. You really should use more than one server to sync to... 4 is
> > generally the recommended minimum.
> > 
> Thanks. Yet more newbie questions:
> 1. Is it better to (a) list 4 sources on the box with the GPS receiver
> attached and just one source on all client boxes that point to it for
> ntp, or (b) list 4 servers on all boxes?

b) It's always best to have 3 (or more) servers for any box running ntp
as it allows the detection of broken servers and helps retain stability
in the event the stratum 1 server has a problem. 1 is a bad number as it
is a single point of failure. 2 is a bad number as it provides no clear
way of detecting who is wrong if the time starts drifting on one of the
> 2. If (b) should I use the "prefer" directive to query the GPS-based
> server first?

No reason as it is stratum 1 and lower stratum clocks (and 1 is the
lowest) are always preferred over stratum 2 or higher.

If you have both your GPS and an external stratum 1 server, you might
want to prefer the internal one, but it would most likely be preferred
anyway as it would likely have lower delay (latency) and jitter.
R. Kevin Oberman, Network Engineer
Energy Sciences Network (ESnet)
Ernest O. Lawrence Berkeley National Laboratory (Berkeley Lab)
E-mail: oberman at es.net			Phone: +1 510 486-8634
Key fingerprint:059B 2DDF 031C 9BA3 14A4  EADA 927D EBB3 987B 3751
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