Mapping and Variants

Andrew Sullivan ajs at
Fri Mar 6 19:27:58 CET 2009

On Fri, Mar 06, 2009 at 12:13:35PM -0500, John C Klensin wrote:

> Well... A different way to look at this is that you can have all
> of the case sensitivity, case-independent matching, and case
> preservation you like in A-labels (as well as all other labels
> that contain ASCII characters and maybe some others).  IDNA does
> not change the DNS.
> A different way to state Erik's observation/suggestion would be
> that, in IDNA-aware "slots" use (on registration, lookup,
> storage in files, etc.) of anything but lower case needs to be
> really strongly discouraged.   That would imply that, in a given
> "slot", the decision that IDNA can be used is a decision that
> upper case is discouraged and violence may be done to it if it
> appears.  That is an application-layer design tradeoff, not a
> statement about the DNS or a problem for 1034.

Actually, putting something like those two paragraphs together might
make this idea rather more palatable.  The more I think about this the
more I think it has a certain appeal.  It has slightly odd effects,
because the traditional DNS case-preservation does go all the way
through an IDNA-unaware application, and does _not_ go all the way
through an IDNA-aware application.  I am going to post a note to
various dns weenies I know to try to get review of exactly this
suggestion, because it does seem to be a way forward.
> FWIW, 1034 could easily have contained a statement to the effect
> that one MUST NOT take a label that one receives, map it through
> a local (as in client-side) aliasing process and then look the
> result up as if it were the original label.   Presumably it was
> omitted because, at the time, everyone thought it was obvious
> (and they probably still do).  But, if 1034 prohibits a strong
> application and registration preference for lower-case native
> character strings in IDNA, that implicit statement would
> prohibit any IDNA mapping at all.


> We are doing a lot of that lately (Erik is certainly not the
> only one).

I have the feeling that may be a charge of which I am guilty, yes.


Andrew Sullivan
ajs at
Shinkuro, Inc.

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