Lookup for reserved LDH labels

Simon Josefsson simon at josefsson.org
Thu Nov 8 10:09:29 CET 2012

Andrew Sullivan <ajs at anvilwalrusden.com> writes:

> On Wed, Nov 07, 2012 at 02:18:37PM +0100, Marcos Sanz wrote:
>> Then it will not be difficult for somebody to point us to the relevant 
>> part in the spec that allegedly states that the lookup algorithm must fail 
>> for reserved LDH-labels that are not XN-labels (e.g. "ad--acta"). I'd 
>> really appreciate if somebody did that.
>    Definitions document [RFC5890].  Putative U-labels with any of the
>    following characteristics MUST be rejected prior to DNS lookup:
>    o  Labels that are not in NFC [Unicode-UAX15].
>    o  Labels containing "--" (two consecutive hyphens) in the third and
>       fourth character positions.
> This is in section 5.4.  Because of the way that section is
> structured, those labels are (at the time of evaluation given the
> protocol definition) actually putative U-labels.

Do you consider "ad--acta" a putative U-label?


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