Re: [idn] naming syntax rules

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

>> >The basic idea here is to declare formal data-types for labels, and
to
>> >incorporate the data-types into syntaxes for applications and
protocols to
>> >use when they need to interact with domain names.
>>
>> While this is good, to make DNS really work the foundamental
>> rules should be the same for all labels. Just like it has been
>> so far.
>
>No, DNS has two rules: octet strings with ASCII, and a hostname subset.

The DNS standard only have one type of label: octet strings with the
code
values 0-127 treated as ASCII during comapring.
The DNS server do not have a hostname subset and may not reject
any name not following it.

For DNS, an A, TXT or SRV record can all contain any octet sequence.

As said in RFC 2929, in practice the labels are text using ASCII even
though
the standard allows any octet value.
Just like the host name rule have been updated several times, the DNS
octet label could now be defined to be just printable text (using UTF-8)

without breaking very many programs. If you add that invalid UTF-8
sequences are treated as just octets even less will break.

>Mailbox names must be case-preserved in order to satisfy protocol
>dependencies, and are not used in lookups so normalization is not
required.

Normalisation is still needed, otherwise may some clients interpret
the name as something else. I could use the ASCII range to encode all
characters I need for Swedish and use that in labels, but you would
not get the right name if you assume they are ASCII.
That is why character data must be normalised.

>Host names have no such dependencies. STD13 defines domain names as
>case-neutral, and enforces this through case-neutral comparison
operations on
>the servers. However, making host names case-neutral will require a new
ACE,
>or will require that every possible case combination be delegated and
managed
>simultaneously. As such, case-neutral comparisons can still be
performed, but
>should be done at the resolver instead of at the server.

Just like some systems have case-sensitive mailboxes, some systems have
case-sensitive host names (Unix is one of them). So you need to retain
case to avoid breaking them.


>The current delegation rules prohibit it. STD13 hostnames are currently
a
>subset of IDN and that should be preserved where possible. Essentially,
this
>change would mean ~"if all of the characters in the delegation are LDH,
then
>the minimum length is 2 characters, otherwise it is one character."

I do not know what you mean by current delegation rules. In .com domain?

Some domains allow 1 character subdomains.

>
>There is no comparison on mailbox names. Mailbox names are not
specified in
>any queries. For RR data, they must be provided in case-sensitive form,
but by
>the same token they must also be non-normalized until the successor to
2822
>says which normalization to use.

RFC 2822 only have ASCII mailboxes.  ASCII is normalised. So there can
be no
non-normalised until we get UCS in mailboxes.

   Dan