Potential Erratum re. length limits in RFC 5890

Vint Cerf vint at google.com
Tue Sep 28 12:07:47 CEST 2010

martin, i see the point and i appears to me that the "characters" language
was intended to mean "octets" as you say.

does anyone else disagree?


On Tue, Sep 28, 2010 at 5:28 AM, "Martin J. Dürst"
<duerst at it.aoyama.ac.jp>wrote:

> In section 4.2, RFC 5890 says
> (http://tools.ietf.org/html/rfc5890#section-4.2):
>                     Because A-labels (the form actually used in the
>   DNS) are potentially much more compressed than UTF-8 (and UTF-8 is,
>   in general, more compressed that UTF-16 or UTF-32), U-labels that
>   obey all of the relevant symmetry (and other) constraints of these
>   documents may be quite a bit longer, potentially up to 252 characters
>   (Unicode code points).
> I'm not at all sure where the number of 252 characters is coming from. It
> does not at all match the justification given here. Punycode is a very
> clever encoding scheme, but it never compresses any character to less than a
> full ASCII character. So on this ground, it is impossible to squeeze more
> than 63 characters into a label.
> The number may have come from my mail entitled
> Re: Definitions limit on label length in UTF-8
> with date and message id
> Date: Sun, 13 Sep 2009 17:05:58 +0900
> Message-ID: <4AACA7E6.1070503 at it.aoyama.ac.jp>
> where 252 is indeed the largest number appearing, but considerations were
> very carefully done in *octets* throughout.
> So I think we should submit an erratum to fix this to 252 octets.
> Regards,    Martin.
> --
> #-# Martin J. Dürst, Professor, Aoyama Gakuin University
> #-# http://www.sw.it.aoyama.ac.jp   mailto:duerst at it.aoyama.ac.jp
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