On Sun, Oct 06, 2024 at 11:58:11AM +0200, Slavko via mailop wrote:
> Ahoj,
>
> Dňa 5 Oct 2024 16:29:26 -0400 John Levine via mailop
> <mailop@mailop.org> napísal:
>
> > A domain name is a sequence of labels, with each label being a string
> > of 65 octets or less. Hostnames are a subset of domain names, where
> > each label consists only of letters, digits, and hyphens.
>
> Yes, from that point of view it is clear, albeit i fell that IDNA RFC
> try to avoid hostname term as possible, perhaps due its ambiguity (or
> due its 24 chars limit?) and introduces LDH term instead of hostname.
>
> Anyway, i understand, that at time when IDNA RFC was born, the
> underscored labels (i mean _service) was not as common (nor clearly
> standardized) as now, but now are common DNS labels.
No, attrleaf labels long predate IDNA 2008, e.g.
_ldap._tcp.<domain> https://datatracker.ietf.org/doc/html/rfc2782
_kerberos._udp.<realname> https://datatracker.ietf.org/doc/html/rfc4120
...
One can reasonably take the view that U-labels are largely a matter of
the user-interface (presentation) layer, the *real* domain name is the
A-label form! But users don't directly work with attrleaf names, these
arise only internally in applications, and applications that support
U-labels should convert names to A-label form *before* adding any
attrleaf prefixes, as part of converting what the user typed to internal
form. Similarly, IDNA A-labels are converted to U-labels as part of
displaying them to the user.
Mind you, the above is my personal perspective, others will disagree,
but I think that it is more likely to keep you out of various kinds of
potential confusion.
--
Viktor.
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