Unconditional punycode conversion

Andrew Sullivan ajs at shinkuro.com
Wed Mar 9 19:16:48 CET 2011

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


Andrew Sullivan
ajs at shinkuro.com
Shinkuro, Inc.

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