Re: [DNSOP] Looking for IANA registry for --xn

<nalini.elkins@insidethestack.com> Thu, 06 October 2016 17:24 UTC

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Date: Thu, 6 Oct 2016 17:24:36 +0000 (UTC)
From: <nalini.elkins@insidethestack.com>
To: Phillip Hallam-Baker <phill@hallambaker.com>, "dnsop@ietf.org" <dnsop@ietf.org>
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Cc: Harish Chowdhary <harish@nixi.in>
Subject: Re: [DNSOP] Looking for IANA registry for --xn
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>I have been looking for the IANA registry in which the IDNA prefix xn-- is allocated and have not been able to find it. I can see the following possibilities

>1) There isn't such a registry. The allocation is purely ad hoc

>2) There is a registry but none of the IDNA RFCs bother to list it as a normative reference.

>Either one would be bad. The existence or non existence of a registry, the allocation or non allocation of a code point is not going to cause me to decide whether or not to use functionality. All that the registry achieves is to avoid collisions.


Phil, this is very interesting.   
The 'xn--', of course, is the prefix for punycode used for International Domain Names.   I have seen it used for DNS resolution quite a bit in the last couple of months.   So, it is certainly used.   In fact, that appears to be the only way one can do DNS resolution (at least in my experience).  That is, do the translation from IDN to punycode.   Then, it seems to work like a charm.
Certainly sounds like an update somewhere is needed.
People may be interested in a draft that Harish and I have just posted:

https://datatracker.ietf.org/doc/draft-elkchow-iea-deploy

>From our section 1.1 which explains punycode:

"Languages not based on the Latin script (A, B, C, etc) use unicode to represent the letters in their alphabet rather than ASCII. Punycode is used to show unicode characters in ASCII format. It is used in the transport of email. 

For example: 
English: NehruHindi: नेहरूPunycode: xn--l2bq0a0bw 

Punycode will start with the prefix: "xn--". An application handling IDN domains has to reference an IDN repository to know how to display them. Emails add to the complication since many email systems pre-date the introduction of IDNs. These systems often simply reject emails that don't work within the old domain name model. 
Nalini Elkins
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