Hal Murray <hmur...@megapathdsl.net>:
>
> e...@thyrsus.com said:
> > I think the solution for this is obvious. We define an extension type the
> > contents of which, if it exists, SHOULD be used as the refid.
> > Implementations that don't know about that extension will be no worse off
> > than before.
>
> Only if they correctly ignore extensions that they don't expect.
What would "not ignoring" look like?
> I'll bet there is a lot of code out there that has never seen an extension
> and does a simple sanity check on the length of a packet assuming there are
> no extensions.
That could be. If it is, we're in the "must design NTPv5" future. But I don't
think we'll know whether we're there unless we field a more conservative design
and get a lot of bug reports.
> [extenstions]
> > Can you be more specific about the past troubles?
>
> Not really. There was a lot of discussion about various complications on one
> of the ntp lists. I didn't follow all the details and/or I may be confusing
> two discussions.
>
> I think the problem was that autokey got tangled up in this area. Maybe a
> few magic lengths had to be avoided. ???
That sounds uncomfortably plausible. I can think of a workaround: add a
padding extension long enough that the packet can't have any of the
magic lengths.
> > I'm already sketching a couple of possibilities for NTPv5 in my head. Both
> > are based on the PNG model of self-describing chunks (which I've heard it
> > iherited from TIFF). One uses binary chunks, like PNG itself. The other uses
> > textual chunks. I could detail-spec either in a couple days' work.
>
> It's not hard if you have a clean slate. It's much more complicated if you
> have to support existing installed gear that won't get updated.
If we're using a new protocol number it's clean slate. If we're not, it
has to be extensions a go-go. I don't see a third alternative.
My heart wants to do a clean-slate design - it is a job I thnk I am
near ideally equipped for by inclination and experience. My head says
that could easily become a deployment nightmare and we should
establish the impossibility of doing an effective job with extensions
first. My head is winning, so far.
--
<a href="http://www.catb.org/~esr/";>Eric S. Raymond</a>
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