[ntp:questions] Mixed maxpoll values for mixed LAN/Internet servers - sensible?

Dave Hart davehart at gmail.com
Fri Feb 27 16:04:44 UTC 2009

On Feb 26, 11:27 pm, "David J Taylor" <david-tay... at blueyonder.neither-
this-bit.nor-this.co.uk> wrote:
> Well, by observation, /all/ the servers are polled at 64s intervals, and
> not just the lan-gps-pps server.

Since your clients are naturally preferring the stratum 1 on the same
LAN, that server's poll interval is clamping your overall poll
interval down with it.  In the similar configuration of a refclock
plus internet servers, if you set minpoll 4 on a reference clock (and
no maxpoll) the similarly unselected internet servers are allowed to
progress to higher poll intervals.  It may not be possible to achieve
the same without a reference clock.

> Yes, I own it, but I don't want to hit on the Internet servers any more
> than necessary, of course.

My suggestion is to pick one ntpd on your LAN to sacrafice the best
LAN timekeeping performance on while providing internet sources to
your LAN in case of problems with the FreeBSD refclock box.  Configure
all the rest of your client ntpds to point to your FreeBSD stratum 1
as well the sacraficial host, using maxpoll 6 on both server lines.
On the sacraficial host, configure the FreeBSD stratum 1 and a nice
wide selection of internet servers, with internet-appropriate maxpoll
(or no maxpoll) on all server lines.  For extra good measure, toss a
"tos minsane 4" in that sacraficial ntp.conf.

That way, all but one of your client ntpds will get the tight
timekeeping available by polling your FreeBSD box at 64s, while they
all retain backup timekeeping via the sacraficial client.  Setting
minsane 4 means there must be 4 sources with a consistent view of the
time before you will synchronize.

If you were only concerned about the refclock failing (such as due to
loss of radio signal) you could achieve much the same by configuring
internet sources on the FreeBSD hosting the refclock.  That wouldn't
help if the power supply fried on the Freebie.

Dave Hart

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