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

Martin Duerst duerst at
Sat Mar 7 13:39:26 CET 2009

At 19:22 09/03/07, Jaap Akkerhuis wrote:

>As you say, there is currently not such a case and it is very
>unlikely that this will ever happen. Some registries do map the
>case (of US-ASCII names) uniformly storing domain names in their
>databases and/or zone files. If you look at the .com zone file,
>you'll note the all names are upper case while in the .nl zone file
>the names are lower case. The original difference in case the
>registrant might have made is very likely lost.  As example, the
>name "NLnetLabs" is just "nlnetlabs" in the .nl zone file (and whois
>information) and would have become "NLNETLABS" in the .com file.

This is new to me, but it is a very interesting fact. It makes it
a bit easier to defend the position that for IDNs, only the lower-
case version really counts (which applies both to IDNA2003 and
IDNA2008, in different ways).

Regards,   Martin.

>So it is just the other way around.  The "don't change case" provision
>was apparently never followed in the context of the registry system
>but only in the DNS protocol.
>       jaap
>PS. I've always assumed this provision was in the protocol because
>at the time its was defined there were systems around with different
>character sets and encoding around. I seems to remember that there
>were quite some systems which knew about the difference in upper and
>lower case, but rendered all character in only one case. So making
>names case ignorant and mapping them to a single form for internal
>use made some sense.
>Isn't this also observed in one of Johns documents?
>Idna-update mailing list
>Idna-update at

#-#-#  Martin J. Du"rst, Assoc. Professor, Aoyama Gakuin University
#-#-#       mailto:duerst at     

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