Re: [dnsext] [Technical Errata Reported] RFC4343 (6361)

[Donald Eastlake <[e-mail]>]

Hi,

Thanks for the recent replies. See below.

On Mon, Dec 28, 2020 at 1:42 PM Evan Hunt <[e-mail]> wrote:
>
> On Wed, Dec 23, 2020 at 09:51:25AM +0100, Kaspar Etter wrote:
> > Thanks a lot for the quick reply. Just to make sure that there’s no
> > misunderstanding: If I figured it out (i.e. I should receive the
> > capitalization of the label as it is in the server’s database in DNS
> > responses), then the deployed DNS DOESN’T conform to this RFC.
> > Examples:
> > dig IETF.org <http://ietf.org/> => IETF.org <http://ietf.org/> in the
answer section of the DNS response
> > dig ietf.org <http://ietf.org/> => ietf.org <http://ietf.org/> in the
answer section of the DNS response
>
> This has been ambiguous for a long time.  If you check the authoritative
> servers for ietf.org, the answer section is capitalized as specified in
> the zone database, not matching the question:
>
>    $ dig +noall +answer @ns1.ams1.afilias-nst.info. IETF.org
>    ietf.org.            1800    IN      A       4.31.198.44
>
> However, some servers use case-insensitive name compression in their
> responses. Differently-capitalized versions of the same name are treated
as
> duplicates, so if IETF.org appears in the question section, the answer
> section will refer back to that.  In my view, this behavior is incorrect,
> but it's commonplace.

Right. "correctness" is in the eye of the beholder but all this pointed out
in RFC 4343 in the Section 4.1 which is the target of this errata:

   ...   No "case conversion" or "case folding" is done
   during such output operations, thus "preserving" case.  However, to
   optimize output, indirect labels may be used to point to names
   elsewhere in the DNS answer.  In determining whether the name to be
   pointed to (for example, the QNAME) is the "same" as the remainder of
   the name being optimized, the case insensitive comparison specified
   above is done.  Thus,
*such optimization may easily destroy the output   preservation of case*.
This type of optimization is commonly called
   "name compression".
(bold face added)

> I'm not sure whether this helps with the issue at hand, I just thought
> the additional context might be useful.

Thanks,
Donald
===============================
 Donald E. Eastlake 3rd   [phone] (cell)
 2386 Panoramic Circle, Apopka, FL 32703 USA
 [e-mail]

> --
> Evan Hunt -- [e-mail]
> Internet Systems Consortium, Inc.