Re: [idn] Determining equivalence in Unicode DNS names

[Stuart Cheshire <cheshire@apple.com>]

Patrik Fältström wrote:
>Example: If a.com and b.com is considered equal,
>why should not a.se and b.se be equal?

a.com. IN A     1.2.3.4
b.com. IN CNAME a.com.

a.se.  IN A     1.2.3.5
b.se.  IN A     1.2.3.6

In this (very simplified) example, "b.com." is declared to be no more
than an alias for "a.com." Any lookup for any DNS record type for
"b.com." will return the same answer as a lookup for that DNS record type
for "a.com."

In contrast, "a.se." and "b.se." are different.

Why is this a problem?

>So, this wg decided that we will use one and only one matching rule,
>just like we decided to use only one character set. Both of these
>(the rule and the charset) are created in the Unicode Consortium.
>
>You also talk about "evolving matching rules over time". That
>is a very bad thing.

Unfortunately, the rules as created by the Unicode Consortium do change
over time. Apple's HFS+ file system uses Unicode file names, with the
restriction (as you would expect) that two files in a directory cannot
have the same name.

Unfortunately, when the Unicode Consortium rules change (we're currently
in the process of moving to Unicode 3.2 rules), this can result in two
files that were previously considered different names, to now be
considered the same name, hence resulting in an apparently invalid file
system.

This is a mess. It would be much better if the file system on the volume
could assert the version of the Unicode Consortium rules by which it
abides, instead of being judged by the version of the Unicode Consortium
rules in effect at the time it is read.

Hence my suggestion that IDN avoid the same mistake, and let the
authoritative server for a domain assert the Unicode Consortium rules by
which it abides.

>Let's say that we have registered apple.com and äpple.com. They
>are considered different. One day the equivalence rule change,
>and they are considered being the same. Who is calling Steve
>Jobs saying that apple.com have to give back it's domain name
>and pick something else? You? ICANN? The registry for .com?

Again, an argument supporting my suggestion that the authoritative server
for the "com" domain should be allowed to assert the Unicode Consortium
rules by which it abides, instead of having to change every time the
Unicode Consortium rules change.

Stuart Cheshire <cheshire@apple.com>
 * Wizard Without Portfolio, Apple Computer
 * Chairman, IETF ZEROCONF
 * www.stuartcheshire.org