I agree,
We should provide better guidance on encoding of the UPN.
This should map with the format of UPN when provided in a certificate.
The reference to the preferred name syntax is thus inherited from RFC
3280. This is how RFC 3280 restricts labels in the dNSName subject alt
name.
I will come back with a proposal on new text later today.
Stefan Santesson
Program Manager, Standards Liaison
Windows Security
-----Original Message-----
From: Mark Andrews [mailto:Mark_Andrews(_at_)isc(_dot_)org]
Sent: den 8 mars 2006 04:23
To: Eric A. Hall
Cc: Kurt D. Zeilenga; ietf(_at_)ietf(_dot_)org
Subject: Re: draft-santesson-tls-ume Last Call comment
On 3/7/2006 8:16 PM, Mark Andrews wrote:
* Hostnames that are 254 and 255 characters long cannot be
expressed in the DNS.
Actually hostnames are technically defined with a maximum of 63
characters
in total [RFC1123], and there have been some implementations of
/etc/hosts
that could not even do that (hence the rule).
RFC 1123
Host software MUST handle host names of up to 63 characters and
SHOULD handle host names of up to 255 characters.
63 is not a maximum. It is a minumum that must be supported.
But even ignoring that rule (which you shouldn't, if the idea is to
have a
meaningful data-type), there is also a maximum length limit inherent
in
SMTP's commands which make the maximum practical mail-domain somewhat
smaller than the DNS limit. For example, SMTP only requires maximum
mailbox of 254 octets, but that includes localpart and @ separator.
The
relationship between these different limits is undefined within SMTP
specs, but its there if you know about the inheritance.
When it is all said and done, max practical application of mailbox
address
is 63 chars for localpart, "@" separator, 63 chars for domain-part.
Anything beyond that runs afoul of one or more standards.
</pedantry>
--
Eric A. Hall
http://www.ehsco.com/
Internet Core Protocols
http://www.oreilly.com/catalog/coreprot/
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--
Mark Andrews, ISC
1 Seymour St., Dundas Valley, NSW 2117, Australia
PHONE: +61 2 9871 4742 INTERNET: Mark_Andrews(_at_)isc(_dot_)org
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