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NTP Issues Today



Blake Dunlap <ikiris at gmail.com> writes:

> That's what happens when you just follow vendor recommendations blindly. If
> you do follow that on vm's (which can actually be a good practice), make
> sure they pull from your own time infrastructure, and not just the world at
> large, and that those servers behave in a sane fashion with regard to time
> jumps.

Emphatically disagree on the "pull from your own infrastructure"
point.  You probably don't have the budget even in a big company for
sufficient diversity of sources [*] for your NTP server and even if
you do the NTP servers will probably be run by the same
person/organization.  Mills has called the latter practice out as bad
in the past.

As Leo pointed out, the key is having a large diverse set so that if a
couple of them go nuts they can be voted off the island.

If you have a requirement for super low jitter or holdover if you lose
network, you're looking at on-site devices with OCXO or Rb frequency
standards in them.  That doesn't mean you shouldn't be talking to the
rest of the world too though.  What if your on-site sources go nuts?
This happens periodically, say every 10 years or so, because of crappy
implementations and worst-current-practices.  A re-read of
https://groups.google.com/forum/?fromgroups=#!search/mills$20ntp$20byzantine/comp.protocols.time.ntp/TryjqtAd1XM/R0zzzE13Tl8J
may prove instructive.

(reading list also includes http://www.amazon.com/dp/1439814635/ )

In my experience NTP beats out even DNS for "blatantly wrong configs
in the wild that nevertheless seem to work well enough that dilettante
tech folks don't notice".

I might have replied to this thread yesterday but I was blissfully
unaware of any problems:

rs at bifrost [8] % ntpq -c peers | egrep -v '(===|remote)' | wc -l
      11
rs at bifrost [9] % 

-r

[*] particularly due to shortsighted US federal government choices on
LORAN, GOES, WWVB time format, etc