Lookup for reserved LDH labels

Simon Josefsson simon at josefsson.org
Thu Nov 8 10:37:04 CET 2012

Simon Josefsson <simon at josefsson.org> writes:

> 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?

Heh, you basically answered "no" on that question here:


So I don't follow why you believe the text above has bearing here,
unless you changed your mind whether "ad--acta" is a putative U-label.

Btw, that thread is useful to re-read.  It contains discussion
overlapping the same issue as is being discussed now.


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