RE: Services and top-level DNS names (was: Re: Update of RFC 2606

"Cellario Luca" <luca.cellario@loquendo.com> Tue, 08 July 2008 13:39 UTC

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From: Cellario Luca <luca.cellario@loquendo.com>
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To: 'John C Klensin' <john-ietf@jck.com>, Bill Manning <bmanning@ISI.EDU>
Date: Tue, 08 Jul 2008 15:39:28 +0200
Subject: RE: Services and top-level DNS names (was: Re: Update of RFC 2606
Thread-Topic: Services and top-level DNS names (was: Re: Update of RFC 2606
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> -----Original Message-----
> From: ietf-bounces@ietf.org [mailto:ietf-bounces@ietf.org] On Behalf Of
> John C Klensin
> Sent: Tuesday 8 July 2008 15:30
> To: Bill Manning
> Cc: Mark Andrews; ietf@ietf.org
> Subject: Re: Services and top-level DNS names (was: Re: Update of RFC
> 2606
>
>
>
> --On Tuesday, 08 July, 2008 04:28 -0700 Bill Manning
> <bmanning@ISI.EDU> wrote:
>
> > On Tue, Jul 08, 2008 at 01:49:24AM -0400, John C Klensin wrote:
> >>
> >>
> >> --On Monday, 07 July, 2008 12:08 -0700 Bill Manning
> >> <bmanning@ISI.EDU> wrote:
> >>
> >> >    John, do you beleive that DNS host semantics/encoding that
> >> > form the bulk      of the IDN work (stringprep, puny-code,
> >> > et.al.) are applicable -only- in   the context of zone file
> >> > generation or are they also applicable in          configuration
> >> > and acess control for DNS?
> >>
> >> I think I don't understand the question.   RFC 3490 tries to
> >> make a distinction between IDNA-aware and IDNA-unaware
> >> applications and domain name "slots".  The intent is, more or
> >> less, to permit a punycode-encoded string with the prefix
> >> (which the IDNA2008 drafts call an "A-label") to appear
> >> nearly anywhere in the DNS but to expect conversion to and/or
> >> from native characters only in contexts where IDNA is
> >> explicitly applied. Even in zone files, IDNA is generally
> >> applicable only to labels and not to data fields.
> >>
> >> >    path/alias expansion/evaluation will be interesting if "."
> >> >    is not what     7bit ASCII thinks of as "."
> >>
> >> RFC 3490 lists a series of other characters that are to be
> >> treated as label-separating dots if encountered in an IDNA
> >> context.  That model causes a number of interesting problems
> >> in contexts where one has to recognize a string as a domain
> >> name, and possibly process it, without knowing anything about
> >> IDNA. The problems show up in situations as simple as
> >> conversions between label-dot-label-dot-label format and
> >> length-label list format, making it very important whether
> >> one identifies an FQDN as containing IDNA labels or converts
> >> it to length-label form first.  IDNA2008 (see the IDNABIS WG
> >> and its documents and mailing list) does away with all of
> >> this as part of a general plan to do a lot less mapping of
> >> characters into other characters.  So, for the proposed newer
> >> version the only label-separating dot permitted in the
> >> protocol is the character you know as 7bit ASCII "." (U+002E
> >> in Unicode-speak).
> >>
> >> Does that answer whatever the question was intended to be?
> >>
> >>    john
> >>
> >
> > perhaps - let me try again w/ example.
> >
> > in my resolv.conf file, I have the following three lines:
> >
> > search . karoshi.com. ip4.int. ep.net.
> > nameserver 198.32.2.10
> > nameserver 2001:478:6:0:230:48ff:fe22:6a29
> >
> > the line of interest is the first line, starting w/ search.
> > the expectation is that the items on this list are domain
> > names. in my case, they are all "fully qualified".   since
> > this is a  configuration file - not a zone file, is IDNA2008
> > expected to  apply?  this data is not, per se, in the DNS.
>
> Nothing in IDNA2008 makes it apply.  Nothing in IDNA2008 even
> makes it apply to zone files (!).   My personal view --others in
> the WG might have other opinions-- is that one would be better
> off using A-labels (the punycode-encoded forms) in this sort of
> context.
>
> The reasoning involves two points:
>
>         * While I don't imagine you would put domain names in
>         your search rules that you couldn't render (or easily
>         type) on your machine, I believe that will happen with
>         some servers who are supporting multilingual
>         communities.  The A-labels can be typed and rendered
>         accurately on any system that can handle construction of
>         the config file (with its ASCII keywords) itself.  The
>         U-labels put you at some risk of seeing little boxes or
>         question marks (or, in some cases, worse) as well as
>         potentially being hard to type.
>
>         * An explicit design goal for IDNA (both versions) is to
>         avoid changing the DNS or low-level DNS implementations.
>         The search rule interpreter in your resolver is going to
>         have to substitute names in that can be used in the DNS
>         and those are the A-labels.  Putting U-labels in the
>         config file would requires that the resolver be
>         IDNA-aware, understand those labels, and map them to the
>         A-label form before doing lookups.  It would also
>         presumably require doing that every time the config file
>         is read, a small decrement in efficiency.
>
> Now, to give you a slightly different answer, I sort of expect
> that communities who use IDNs a lot, especially those for whom
> typing ASCII is uncomfortable, will find that IDNs drive them
> toward "compilers" or special user interfaces to aid them in
> producing all sorts of config files.  I'd expect them to develop
> tools to permit constructing zone file and resolver config file
> templates with IDN U-labels in them and then translating them
> into DNS-internal forms (i.e., with the A-labels).  I'd even
> expect such tools to provide screen interfaces that permit
> working with the keywords of the config files without having to
> type them out (a process that gets error-prone if words like
> "search" or "nameserver" or "$ORIGIN" are not familiar and/or
> the keys to enter them aren't on the keyboard).
>
> But those are local tools, not part of anyone's protocol or
> global facilities.
>
> Again, just IMO.
>
>    john
>
>
>
>
>
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