Lookup for reserved LDH labels

Marcos Sanz sanz at denic.de
Wed Nov 7 17:57:06 CET 2012


> Personally, I find it hard to reason that the WG intended to
> forbid/ break labels that were registered/delegated and
> perfectly valid under IDNA2003 but still intended to allow
> lookup of labels associated with other prefixes (or, for that
> matter, labels containing non-ASCII characters but coded
> directly in UTF-8) to be looked up in the public DNS.

for me, though, it is crystal-clear, since I read in RFC 5891 section 5 under the title "Domain Name Lookup Protocol" explictly
"the lookup-side tests are more permissive and rely on the assumption that names that are present in the DNS are valid."

The tests listed in bullets under Section 5 were not planned for ASCII labels, only for putative U-Labels. Furthermore section 5 ends with the

"For all other strings, the lookup application MUST rely on the presence or absence of labels in the DNS to determine the validity of those labels and
the validity of the characters they contain."

, which is exactly what you claim you find hard to reason.

So, personally, I'd find it very hard to swallow that "ad--acta.de" is now an invalid domain if your only argument is: "it's not in the standard,
actually even the opposite might be interpreted out of it, but believe me, it was meant differently".


> What about instead, in 5.1,
> the following:
>     If the string is an NR-LDH label, it proceeds directly to DNS Name
>     Resolution (see Section 5.6).

though I find the text redundant, I am all for it if it helps as a clarification for implementors.


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