Subject: QType: ADDR (was Re: !! DANGER -- POTENTIAL FUD -- DANGER !!)

From: Derek Atkins <[email-masked]>
Date: 07 Aug 2002 19:41:01 -0400

"Eric A. Hall" <[email-masked]> writes:

> It occurs to me that an easy prevention against this potential problem
> (OKAY ITS FUD, SHEESH) would be define a new query-type for addresses,
> similar to the old MAILA and MAILB qtypes. Rather than issue two queries
> for AAAA plus A, and rather than issue a qytpe=ALL, v6-aware applications
> could issue the qtype=ADDR (or whatever). More efficient.

Why is this FUD?  This is an interesting proposal..  I'm not sure if
it is reasonably implementable, but it's still interesting.  In
particular, I don't know what kind of failure characteristics this
would have.  Is there a preference of AAAA over A?  Would it imply
that if no AAAA exists you would have to provide the NXT to prove
it?

-derek

-- 
       Derek Atkins, SB '93 MIT EE, SM '95 MIT Media Laboratory
       Member, MIT Student Information Processing Board  (SIPB)
       URL: http://web.mit.edu/warlord/    PP-ASEL-IA     N1NWH
       [email-masked]                        PGP key available

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From: "Eric A. Hall" <[email-masked]>
Date: Wed, 07 Aug 2002 19:19:58 -0500

on 8/7/2002 6:41 PM Derek Atkins wrote:

> what kind of failure characteristics this would have.  Is there a
> preference of AAAA over A?

I would think that the application would determine its own preference for
the returned data.

The big concern is with caches. They would have to be limited somewhat.
For example, they couldn't answer the query with cached data unless they
had positively absolutely passed another qtype=addr or distinct qtype=A
and qtype=AAAA queries. Otherwise, they could return any A RRs which had
been cached but not AAAA RRs (or vice versa), resulting in an incomplete
and erroneous view of the complete answer, thereby causing the client to
make the wrong decision.

> Would it imply that if no AAAA exists you
> would have to provide the NXT to prove it?

I disclaim any expertise on DNSSEC.

-- 
Eric A. Hall                                        http://www.ehsco.com/
Internet Core Protocols          http://www.oreilly.com/catalog/coreprot/

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From: Derek Atkins <[email-masked]>
Date: 07 Aug 2002 20:28:16 -0400

> I would think that the application would determine its own preference for

So the qtype=addr would have you return _ALL_ data, both AAAA and A?
Couldn't that be a rather large response?  If not, then how does the
_server_ know which type to prefer in the response?

> and erroneous view of the complete answer, thereby causing the client to

Caches are already going to have to do this for proper NXT processing.

> I disclaim any expertise on DNSSEC.

Well, you (in general, not Eric Hall specifically) need to think
about how it would interact with DNSSEC.

-derek

---

From: [email-masked]
Date: Thu, 08 Aug 2002 09:52:28 +0900

>> On the other hand, my bet is that more applications are likely to START
>> doing it once we have IPv6 applications that query for qtype=any instead
>> of doing AAAA before A.

	"any" query does not return all available data.  it is allowed for
	a recursize resolver (named) to return data on the cache already, and
	not with other records actually available.  therefore, stub resolvers
	(libc resolver) that makes "any" query will not work.

tojun

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From: Rob Austein <[email-masked]>
Date: Wed, 07 Aug 2002 23:24:39 -0400

> that if no AAAA exists you would have to provide the NXT to prove

It's not FUD, but I don't think it works: if there's more than one
distinct RRset that can satisfy a particular query, you can't predict
which RRset(s) you're going to get back in the response unless you're
talking to the authoritative server.  Additional section processing
doesn't count, since in all but a few (reasonably well-understood)
cases the additional section is just an efficiency hack and one can
just query explictly for whatever one might have wished to find there.

This is basicly the same problem as we have with QTYPE=*, hence the
occasional reference you might see in old namedroppers archives to
MAILA and MAILB as "semi-wildcards".

---

From: Markku Savela <[email-masked]>
Date: Thu, 8 Aug 2002 09:01:20 +0300

> From: Derek Atkins <[email-masked]>

> _server_ know which type to prefer in the response?

Just a thought occurs...

Instead of having a new query type 'addr', could we just define that
AAAA query returns both IPv4 and IPv6 addresses? (And if you want
uniform format in reply, put IPv4 addresses into IPv4 mapped format)

Unfortunately, due to already existing implementations of AAAA in
servers, resolvers would always have to do the A query too (if AAAA
doesn't have any IPv4 addresses), but if it did, then it could
consider it a "new AAAA" reply and skip A.