Re: [idn] Which names are valid? (was How should labels be encoded?)

["Adam M. Costello" <amc@cs.berkeley.edu>]

David Hopwood <david.hopwood@zetnet.co.uk> wrote:

> In a query for SRV records, a non-LDH character ('_') is used in the
> query string (QNAME), not just the response.

I stand corrected.  I was not aware that non-LDH characters were welcome
in DNS queries.

This raises the question:  Is _ldap._tcp.example.com a domain?  Or is it
a creature like the mailbox field of SOA records, a sequence of labels
that does not name a domain?

Could the name server for example.com contain SOA and NS records for
_tcp.example.com, and the name server for the latter contain the SRV
record for _ldap._tcp.example.com?  If we want the answer to be yes,
then _ldap._tcp.example.com must really be a domain.  If the answer is
no, we could say it's not a domain, just a sequence of labels, of which
all but the first two form a domain name, and IDNA would apply only to
those labels.

Perhaps nameprep is not the right layer for the non-LDH ASCII
prohibition.  Maybe that belongs at a higher layer, the same layer that
checks for beginning/ending hyphens.  In other words, put all the checks
related to preferred name syntax in one place, where they can be skipped
if they don't apply.

By the way, I already had plans to make a slight change to AMC-ACE-Z
so that all ASCII characters are encoded literally, not just LDH
characters, because it makes the encoder slightly simpler, and has no
effect for names that avoid non-LDH ASCII characters.

AMC