No case change in DNS (was: Re: Mapping and Variants)

Troy tjk at
Sat Mar 7 10:28:06 CET 2009

I wanted to clarify something here:
DNS does preserve the case, e.g. when querying wWw.W3.OrG. The browser
is a different matter. E.g. the URI RFC RFC3986 (STD66) talks about
changing a hostname to lower case. I.e. HTTP and URI standards are not
part of the DNS system. 

To rephrase what you said, it will be impossible to focus solely on DNS
when discussing rules for IDNA local mappings. At least the SMTP and
HTTP protocols' rules must be taken into consideration.


Troy Korjuslommi
+358 40 570 9900
Tksoft Inc.

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At 03:27 09/03/07, Andrew Sullivan wrote:

Hello Andrew,

Can you shed some light on the "don't change case"
provision in RFC 1034?

In my understanding, it would make very much sense during
registration. It could also make sense for the eventuality
that some parts of the DNS don't do case-equivalent lookup.
(Don't know whether there is currently such a case.)

[it seems that was the original motivation; RFC 1034,
on page 8, says:
                                      The rationale for this choice is
that we may someday need to add full binary domain names for new
services; existing services would not be changed.

However, it definitely does not make sense, and isn't
respected, e.g. in a Web context. I just typed in
http://wWw.W3.OrG/ into my browser, and after a return,
I got back the page, and http://wWw.W3.OrG/ was changed
to After all, the point of entering
(for non-IDN domain names) the case variant preferred
the registrant into the domain name system is just so that
this can be shown to an end user after lookup, or not?

Also, similar mappings are done over and over by Web caches
and spiders even without any resolving activity. It increases
efficiency too much to not be done, even if it would be
prohibited in some RFC.

In the context of the present discussion, wouldn't the only
thing that would be happening, even if we went for "lowercase
when you can" rather than just the "strongly discourage
upper case" as proposed by John, be that what happened
above on resolution was just 'pre-applied' in a Web
context, where (ASCII) case equivalence is baked into the
specs, see e.g. Section 3.2.3 of RFC 2616 (HTTP) and 3.2.2
of RFC 3986 (URIs).

Regards,    Martin.

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