ntp config tech note
Michael Sinatra
michael at rancid.berkeley.edu
Fri May 21 04:16:41 UTC 2004
Robert E. Seastrom wrote:
>
> "Hannigan, Martin" <hannigan at verisign.com> writes:
>
>
>>That's NTPv4 isn't it?
>>
>>I also prefer to use three peers vs. two. Always an odd number,
>>greater than 1. Assumptions can't be made about the mathematics
>>behind time, but in a reference model, odd numbers are better.
>
>
> Actually, three is not enough; Mills says at least four. Diversity in
> manufacturer (and controlling organization if you can spare the
> cycles) is a big big plus. You may wish to read Dr. Mills' post to
> comp.protocols.time.ntp in the wake of the TrueTime bug of the
> 2001->2002 new year:
>
> http://groups.google.com/groups?hl=en&selm=3C32924F.994E1D01%40udel.edu
If you're really paranoid, diversity in reference sources should also be
considered. You should have more than one stratum-1, and as a group
they should get time from more than one of [GPS,
WWV/WWVB/DCF77/CHU/JJY/ETC., USNO, ACTS, etc.] and your stratum>1s
should get time from multiple stratum-1s of similarly diverse references.
Many NTP folk look down their nose at the radio sources, since GPS is
more accurate. But if you already have a GPS stratum-1, then perhaps
your next stratum-1 should be WWVB and friends, or you should have a
backup assocation with someone who does. And remember that CDMA gets
its time from GPS, so it doesn't "count" as a diverse source. Like I
said, if you're really paranoid...
michael
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