[ntp:questions] NTP Pool rules vs. four-server advice

Danny Mayer mayer at ntp.isc.org
Tue Dec 20 02:29:05 UTC 2005


Michael Deutschmann wrote:
> I've noticed a conflict between the instructions on the NTP server Pool
> project page and other NTP advice.
> 
> It is commonly advised here to configure ntpd either to slave to 1
> server, or to track 4 or more.  The reason being that, when not slaving
> blindly to one server, NTP's algorithms require 3 good servers, and if you
> know all three will remain good, you may as well blindly track one.
> 
> In contrast, the NTP Pool directions explicitly say to use only 3 pool
> servers when using the pool alone, and only 2 if you have a local
> timeserver at your ISP.  Presumably this also means only 1 pool server if
> you have 2 others, and no pool servers if you have three or more others.
> 
> The intersection of these two rules mean the only possible answer is to
> use one pool server with no backup, or no pool servers at all.
> 
> This means that the [012].*.pool.ntp.org hostnames are of no legitimate
> use.
> 
> 
> At present, I have my border NTP server slaved to my ISP's timeserver.
> But that computer went nuts as of last Friday (It's in an endless loop
> cycle of about twenty minutes -- it keeps letting the offsets to it's
> reference servers drift to -2.8s and then resetting itself.), so I'm
> considering adding the pool as a fallback.  But following all the rules,
> this is impossible.
> 
There's no requirement that you only use NTP servers from the pool. I
don't use them at all. The pool people may not want you to use too many
of the servers but that is a different matter altogether.

Danny



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