[dns-operations] IDNA vs. dig vs. non-IDN labels.

[Viktor Dukhovni]

> On Jan 6, 2021, at 2:01 PM, Andrew Sullivan <ajs at anvilwalrusden.com> wrote:
> 
> Because if you're doing IDNA you have to permit only A-labels and NR-LDH labels, according to RFC 5890.  NR-LDH labels are defined in §2.3.2.2, but refer to §2.3.1.  In there is this text:
> 
>   [An LDH label] is the classical label form used, albeit with some additional
>   restrictions, in hostnames [RFC0952].  Its syntax is identical to
>   that described as the "preferred name syntax" in Section 3.5 of RFC
>   1034 [RFC1034] as modified by RFC 1123 [RFC1123].  Briefly, it is a
>   string consisting of ASCII letters, digits, and the hyphen with the
>   further restriction that the hyphen cannot appear at the beginning or
>   end of the string.  Like all DNS labels, its total length must not
>   exceed 63 octets.

That mostly makes sense on *input*.  But on *output*, when one has
a wire-form DNS name, and is computing a prentation form, if the
wire-form label does not start with "xn--" it makes no sense at
all to apply IDN conversion, or apply rules that pertain to
hostnames for a name that is not a hostname.

So while I acknowledge that one can always specify "+noidnout",
I strongly concur that this is a "dig" bug.  Not a showstopper
by any means, but something worth fixing.

-- 
	Viktor.