idnabis-defs-10: R-LDH labels that are not prefixed with "xn--"

John C Klensin klensin at jck.com
Sun Aug 30 20:29:41 CEST 2009



--On Monday, August 31, 2009 4:02 AM +1000 Wil Tan 
<wil at cloudregistry.net> wrote:

> Dear IDNAbis WG members,
> First, my apologies for having not noticed or raised this
> earlier.
>
> In idnabis-defs-10 section 2.3.1 paragraph 5:
>
>    Labels within the class of R-LDH labels that are not
> prefixed with    "xn--" are also not valid IDNA-labels.  To
> allow for future use of    mechanisms similar to IDNA, those
> labels MUST NOT be processed as    ordinary LDH-labels by
> IDNA-conforming programs and SHOULD NOT be    mixed with
> IDNA-labels in the same zone.

Unless, in the moving around of text, we have slipped up, it is 
important to note that the restriction here applies _only_ to 
IDNA-aware applications.  That prevents it from being a 
restriction on the DNS generally.   However, for IDNA-aware 
applications, it is a precaution against possible future 
prefix-altering changes as well as something of a mechanism for 
making it harder for bad guys to game future changes.  If any 
non-IDNA arrangements come along that use "??--" label 
encodings, they will of course have to be coordinated with each 
other and with IDNA; in the interim, this provision keeps IDNA 
out of their way (i.e., avoids preempting such approaches).

And, yes, the WG did discuss this at great length.

> I may have missed it, but don't recall any discussions about
> restricting the processing of other tagged domains. Is this
> the right draft to prescribe restrictions on how non-XN-Labels
> are processed?

IMO, we are much too tied up in special definitions and 
confusing terminology already.  Please let's not make it worse 
by introducing more unnecessary terminology in the form of 
"tagged domains".  And it is the right place for defining how 
IDNA-aware applications handle R-LDH labels that are not valid 
A-labels, at least IMO and in the opinion of the mailing list 
the last two or three times we went through that topic.

best,
    john





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