[DNSOP] the ??-- thing (was Re: I-D Action: draft-huston-kskroll-sentinel-04.txt)

Andrew Sullivan <ajs@anvilwalrusden.com> Thu, 01 February 2018 21:20 UTC

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From: Andrew Sullivan <ajs@anvilwalrusden.com>
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Subject: [DNSOP] the ??-- thing (was Re: I-D Action: draft-huston-kskroll-sentinel-04.txt)
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Please note that this is not about the document that started this
thread.  It's a rathole, but in a different field.

On Tue, Jan 30, 2018 at 04:58:01PM -0800, Paul Hoffman wrote:
> Please, no. As the originator of the original
> <letter><letter><hyphen><hyphen> hack, I think this is the wrong thing to do
> for many reasons. The biggest one is, sadly, the fact that some software now
> has <letter><letter><hyphen><hyphen> as reserved even though it should not.

I am not convince that "it should not" is true, and having thought
about this a little more it seems to me that an IANA registry should
have been created in the first place for this sort of miserable
in-label hack.  If it had been, we could have done something useful
here.  And if we don't do so now, in short order we're going to be
into the multi-level underscore-label hell that underscore labels are.

RFC 5891 explicitly says that any IDNA-handling software can't accept
a string with two hyphens in the third and fourth character positions
(that is, in a crappy regex, can't take ^..\-\-.*) as a candidate
Unicode string to be a label (see  This causes upset in
section 5.4 of the same document, which is I suspect how Paul's "sad"
software came to be.

It seems plain therefore that a registry of in-band in-label prefixes
ought to be created, so that instead of heuristics in IDNA2008 we
could tell people to use a real rule.

Before I go to the bother of writing this up, are there at least five
people who would review it, noting that it must update RFC 5891 to be



Andrew Sullivan