Unconditional punycode conversion

Simon Josefsson simon at josefsson.org
Wed Mar 9 19:27:47 CET 2011

Andrew Sullivan <ajs at shinkuro.com> writes:

> On Wed, Mar 09, 2011 at 07:08:45PM +0100, Simon Josefsson wrote:
>> I don't see any of this reflected in RFC 5891.  As far as I can tell,
>> "ab--cd" is permitted since there is no rule to forbid it.
> RFC 5891 isn't the only normative document in the series.  RFC 5890 is
> also normative.  You need to read all the documents together.
> But anyway, "Forbidden to whom?"  ab--cd is a perfectly legal DNS
> label.  So, for that matter, is ƒoregoneconclusion and 3ßçç~µ.  Any of
> these could appear in a legal DNS zone today.
> But, under IDNA2008, there are only three types of valid labels:
> A-labels, U-labels, and NR-LDH labels.  ab--cd is not in any of those
> categories, and is therefore not valid under IDNA2008.  This is quite
> explicitly stated in RFC 5890 section≤
>> Is a new rule needed to forbid "ab--cd" in RFC 5891 or is there an error
>> in the existing "--" rule for U-labels, or something else?
> Why does 5891 have to say anything about this?  5890 defines the
> terms.

My reading has been that RFC 5891 section 5 specify the steps needed to
validate a domain name before it is looked up.  If there is no rule in
there to invalidate "ab--cd" the label will be looked up.  Is this
reading not the intended one?


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