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Re: An Internet-Draft on literal scoped addresses with accompanying zone IDs in URIs

From: Bill Fenner <fenner@research.att.com>
Date: Fri, 19 Nov 2004 15:57:06 -0500
Message-Id: <200411192057.iAJKvAr18036@windsor.research.att.com>
To: bob.hinden@nokia.com
Cc: ipv6@ietf.org, uri@w3.org


>I think loosing the ability to cut and paste these addresses is a 
>problem.  The % is in widespread usage today.

Indeed, that's why this whole thing is a sticky issue and there's
no obvious answer.  My FreeBSD and MacOS machines all use the % too,
and have for years.

>My dump question (that exposes my lack of knowledge about URIs/etc.) is 
>since the literal IPv6 address are enclosed in "[" "]" to allow for the ":" 
>in the literal IPv6 address, why can't the "%" be used in the same 
>way?  For example:
>
>   http://[fe80::20d:60ff:fe2f:8df5%4]
>
>Please excuse my ignorance on this, but it would be good to explain this 
>(and include this information in the draft).

You're right, we probably distilled the discussion a little too
much.  We should add a third entry to the list and list its pros
and cons for a bare %.

The basic issue is how special % is in URLs, because of
percent-encoding.  Section 2.4 of draft-fielding-uri-rfc2396bis
(the full Standard URI spec, currently in the RFC-Editor's queue)
says:

   Because the percent ("%") character serves as the indicator for
   percent-encoded octets, it must be percent-encoded as "%25" in order
   for that octet to be used as data within a URI.

The newer IRI spec (in IESG Evaluation; draft-duerst-iri-10.txt)
specifies an encoding of URIs to IRIs that assumes that any percent
anywhere in the URI begins a percent-encoded octet.  Allowing a
bare "%" would complicate these rules quite a bit.  There would be
no way to know without parsing the URI further whether the % began
a %-encoded octet or not.  (An accidental example of how ambiguous
this can be is the one of the link-local addresses of my home system:
fe80::240:5ff:fe42:d6de%de1 - %de is a legal percent-encoded octet,
or the introduction of a zone ID "de1".)

  Bill
Received on Friday, 19 November 2004 20:57:11 GMT

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