Re: IDNA applicability: per RR/Class or DNS-wide

John C Klensin <[email protected]> wrote:

> (i) The DNS now has different rules for valid label forms and
> parameters for different RR types (e.g., "A", "MX", etc., are
> recommended to contain only LDH names, while "SRV" uses names that
> are in ASCII but violation LDN norms) and the core DNS specification
> clearly anticipates an even broader range of names/ labels.  IDNA
> should recognize this and anticipate the use of different "foo-prep"
> profiles of stringprep with different RR types and/or classes, rather
> than forcing everything into a "nameprep" model.

Different validity rules is not at all the same thing as different
profiles.  The profile is mainly about how labels are compared.  In
DNS now, the same comparison rules apply to all labels.  If we allow
multiple profiles, that's the same as allowing different comparison
rules for different labels.

I have no problem with different RR types imposing additional
restrictions on what is valid.  IDNA already anticipates restrictions in
addition to (not instead of) Nameprep:

    It is expected that some name-handling bodies, such as large zone
    administrators and groups of affiliated zone administrators, will
    want to limit the characters allowed in IDNs further than what
    is specified in this document, such as to prohibit additional
    characters that they feel are unneeded or harmful in registered
    domain names.

AMC