Stupid U-label question [correction]

Vint Cerf vint at google.com
Tue Aug 19 22:51:28 CEST 2008


Tina that was my reaction too

----- Original Message -----
From: idna-update-bounces at alvestrand.no <idna-update-bounces at alvestrand.no>
To: Frank Ellermann <hmdmhdfmhdjmzdtjmzdtzktdkztdjz at gmail.com>; idna-update at alvestrand.no <idna-update at alvestrand.no>
Sent: Tue Aug 19 13:40:44 2008
Subject: RE: Stupid U-label question [correction]

Hi Frank, im sorry but im just not following this.

A domain name cannot begin with "xn--" unless it is an A-label. Your "u2" below is not an A-label as far as I can tell.


Tina


> -----Original Message-----
> From: idna-update-bounces at alvestrand.no [mailto:idna-update-
> bounces at alvestrand.no] On Behalf Of Frank Ellermann
> Sent: Tuesday, August 19, 2008 11:22 AM
> To: idna-update at alvestrand.no
> Subject: Re: Stupid U-label question [correction]
>
> Sorry, several typos and an error, new attempt:
>
> | I *think* we have it clear that LDH-label means
> | what the name says, a DNS domain label (1..63
> | octets) limited to ASCII letters, digits, and
> | hyphen; not starting or ending with a hyphen.
>
> [...]
>
> | Let u1 = ä (umlauted a), that's A-label xn--4ca.
> | Let u2 = xn--4caä, and use punycode *directly*
> | to bypass the RFC 3490 4.1 (5) restriction.
> |
> | That results in A-label xn--4ca-cxa.  Therefore
> | in theory u2 could have A-label xn--xn--4ca-cxa
> | IFF that is not prohibited somewhere in IDNA200X.
>
> No u3 involved, I need more coffee.
>
>  Frank
>
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