Re: [dnsext] BADVER/FORMERR

In message <20111115153055.205a61dff9fc1684c258b274662bb912.4a8b265d31.wbe@emai
l00.secureserver.net>, "Michael Sheldon" writes:
> 
> > Part of Mark A's argument is that the semantics for QDCOUNT = 0 should
> > be considered well defined because no standard query processing is
> > involved if there is no question to process.
> 
> Really? Exactly what part of any RFC defines what should be returned on
> a QUERY where QDCOUNT == 0? Unless you found something I haven't seen,
> it's not only not well-defined, it's not defined at all. 

Actually if you follow the algorithm you end up with NOERROR.  Most of
the steps become no-ops.

Set or clear RA.
There is no QNAME so you can't find a zone.
There is no QNAME so you can't recurse and add records.
There is no additional data to add.
You return the response which is empty/NOERROR.

> > Furthermore, he noted that an empty question section is (trivially)
> > parsable, and cites three plausible scenarios where such a query might
> > be useful.
> 
> He defines circumstances where he can learn things from the server by
> deliberately sending invalid data, thus eliciting an error message. So
> we've already defined that he's deliberately sending contextually bogus
> data. The question is, if everything in the EDNS section is correct,
> what would the response be to QDCOUNT=0? Unless you can convince me
> there is a valid non-error response to this, I see nothing wrong with
> returning a response based on the first error I find and discontinuing
> parsing at that point. In my opinion, a query with no query is a format
> error. Any further errors beyond that point are irrelevant.

QCOUNT > 1 is hard because there is one rcode and more that one possible
response.

QCOUNT = 0 gets rid of all name based acl processing.
QCOUNT = 0 is independent of the zones being served.
QCOUNT = 0 in plain DNS gives you a test to see if the server is
alive, whether it will recurse for you or not (RA), and whether it
will in general answer queries for you.

Note QCOUNT > 1 is a valid in a response to a IQUERY.

> My suggestion Mark, is to put some kind of question in the packet, the
> size difference is frankly insignificant.

> Michael Sheldon
> Dev-DNS Services
> GoDaddy.com
> 
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-- 
Mark Andrews, ISC
1 Seymour St., Dundas Valley, NSW 2117, Australia
PHONE: +61 2 9871 4742                 INTERNET: marka@isc.org