Harald Tveit Alvestrand wrote:
In my opinion, we should never introduce any function that involves the
DNS where:
- the answer is required to be different for different requestors
- the answer has to be different at two times separated by less than
~seconds
- a temporary failure of the resolution process is a fatal error rather
than a delay
These strike me as some really excellent, basic requirements, for any DNS usage.
Offhand, I don't see why the second bullet isn't stronger. Althought there
are many scenarios in which the producer of DNS responses might choose to make
responses be different over time (or for that matter, different for different
requestors) I see these as local implementation choices, rather than being
built into the definition of the standardized service. Hence, I do not see
why the answer *ever* "has to be" different. That said, I suppose we could
use Postelian language, of the style "until something changes", where a
machine's getting a new IP Address is an obvious example.
Since the terms "mediated" and "signalling", in the way I commonly use
them, violates the first of these points in almost every design I'm
aware of, I think those are lousy terms to use for any function that the
DNS is good for.
The reason I introduced the term signalling was precisely because setting
up a connection today involves more than naming. Saying that the DNS
should be the exclusive naming infrastructure is not a new position. What
I am saying is that today session initiation involves more than the DNS
and that this makes the IPv4/IPv6 transition more difficult than it
should be.
I did not initially see why the term "signalling" might be causing heartburn,
with respect to the DNS. But the (entirely reasonable) view that "signaling"
means "an exchange of control information among participants as part of the
establishment of an association, then no, the DNS does not qualify.
By way of example, having TCP use domain names would make the DNS be part of
the signaling mechanism, I think. But it's current role is carefully kept
separate from that.
(Multi-addressing designs that use domain names might therefore be viewed as
making the DNS be part of a signaling mechanism, which of course explains why
so many IETF infrastructure folk have had heartburn about that dependency.)
d/
--
Dave Crocker
Brandenburg InternetWorking
bbiw.net
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