Pivoting

[Gary E. Miller]

Yo Eric!

On Sun, 23 Apr 2017 17:44:20 -0400
"Eric S. Raymond" <esr at thyrsus.com> wrote:

> Achim Gratz <Stromeko at Nexgo.DE>:
> > I don't think ntpd needs to do any pivoting _except_ at startup
> > time, where it is unavoidable and it should attempt to do anything
> > after it has started up.  
> 
> Huh?  Potentially you need to apply a pivot to every packet that
> comes in; different sources could even have different epochs. 

Not really.  2s complement fixes it for packet up to many years
apart.  Remember, all ntpd uses, after the first time, is time deltas.

I would be happy to write test cases that show this.

> > For setting the initial time you'll want to have as many
> > independent bounds on the time as you can provide, since you
> > potentially cannot trust _any_ of the possible sources. 
> 
> True.  But it is not clear what we can do about this other than what
> we are already doing - that is, pull in lots of sources, discard
> outliers, make a best guess.

If we could mandate using the leap file, can we assume the leap file
has been updated in the lst 68 years?

> > One assumption delivering a single bound.  The other assumption is
> > that the system time is already close enough for ntpd to not need
> > to pivot again. Getting time over HTTPS[*] could deliver a third
> > venue to start doing a majority vote.
> > 
> > [*] http://phk.freebsd.dk/time/20151129.html  
> 
> Instead of trying to use this for precise time, we could try using a
> Date just at startup to figure out what era we are in.

Except for ntpd that is not net connected.  A more common condition
than I would have thought.

RGDS
GARY
---------------------------------------------------------------------------
Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97703
	gem at rellim.com  Tel:+1 541 382 8588

	    Veritas liberabit vos. -- Quid est veritas?
    "If you can’t measure it, you can’t improve it." - Lord Kelvin
-------------- next part --------------
A non-text attachment was scrubbed...
Name: not available
Type: application/pgp-signature
Size: 488 bytes
Desc: OpenPGP digital signature
URL: <https://lists.ntpsec.org/pipermail/devel/attachments/20170423/3dea7627/attachment.bin>