RE: [idn] Forbidden characters

[Dan Oscarsson <Dan.Oscarsson@trab.se>]

>> If we define that nameprep must be done before names are sent 
>> over the DNS protocol we get a lot of characters that are 
>> forbidden in host names.
>> 
>> For example: all upper case letters, double width and circled letters.
>> 
>> This is quite a change from current usage where both upper 
>> and lower case is allowed in host names.
>
>They are not forbidden: they will get folded to something else. So you can
>still write and register your names with, say, U+00DC LATIN CAPITAL LETTER U
>WITH DIAERESIS and U+2462 CIRCLED DIGIT THREE. They can be used in your
>applications and by your users. They are just strictly euqivalent to U+00FC
>LATIN SAMLL LETTER U WITH DIAERESIS and U+0031 DIGIT ONE. Just like 'A' and
>'a' are strictly equivalent today in DNS.
>

But today the name service itself can handle both 'A' and 'a', and you
can register a name with 'A' in it. When nameprep is required to be
done before a name enters the name service, the name service cannot
itself handle the above characters. So in the name service they are
forbidden and cannot be returned from it.
So for the DNS service (which includes the DNS servers and the protocol)
the characters are forbidden.

   Dan