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Network Working Group                                          B. Fenner
Internet-Draft                                     AT&T Labs -- Research
Expires: August 23, 2005                                       M. Duerst
                                               World Wide Web Consortium
                                                       February 19, 2005


        A Format for IPv6 Scope Zone Identifiers in Literal URIs
                      draft-fenner-literal-zone-01

Status of this Memo

   This document is an Internet-Draft and is subject to all provisions
   of Section 3 of RFC 3667.  By submitting this Internet-Draft, each
   author represents that any applicable patent or other IPR claims of
   which he or she is aware have been or will be disclosed, and any of
   which he or she become aware will be disclosed, in accordance with
   RFC 3668.

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   This Internet-Draft will expire on August 23, 2005.

Copyright Notice

   Copyright (C) The Internet Society (2005).

Abstract

   This document specifies the format to be used when specifying a zone
   identifier with a literal IPv6 address in URIs and IRIs.  While this
   combination is expected to be needed rarely, it is important to
   specify the exact syntax.




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1.  Introduction

   RFC 3986 [RFC3986] defines the IPv6address production for the rare
   case that a literal IPv6 address is required in a URI.  IRIs
   [RFC3987] copy this syntax.  The IPv6 Scoping Architecture
   [ipv6-scoping-arch] describes the syntax for specifying a zone ID to
   disambiguate an ambiguous scoped address.  Unfortunately, the
   IPv6address production does not permit the format including the zone
   ID, so this document defines a method to specify a zone ID with a
   literal IPv6 address.

2.  Format

   The IPvFuture production in URIs and IRIs was created to allow for
   flexibility in defining new IP address formats.  We use this
   flexibility in this format, to add a previously unanticipated address
   format for IPv6.  Therefore, strings matching this grammar also match
   the IPvFuture production in URIs and IRIs.  While the form specified
   in the IPv6 Scoping Architecture [ipv6-scoping-arch] uses a percent
   ("%") to separate the zone ID from the address, this form separates
   the zone ID from the address using an underscore ("_"), to avoid the
   special meaning of the percent ("%") in URIs.


   ; An address matching IPv6scoped-literal also matches
   ; the URI/IRI spec's IP-literal with IPvFuture
   IPv6scoped-literal = "[v6." IPv6scoped-address "]"
   IPv6scoped-address = IPv6address "_" IPv6zone-id
   IPv6zone-id = 1*( unreserved / sub-delims / ":" )


2.1  Tradeoffs

   o  Use _ or Z or some other character as separator.
      Pro:
         +  Fits current ABNF.
         +  Doesn't require confusing percent-encoding.
      Con:
         +  Have to remember different separator.
         +  Can't copy and paste from other forms.  (But that is the
            case also for percent-encoding, which usually doesn't happen
            automatically.)
      Issues:
         +  Zone ID is currently loosely specified in scoping-arch; in
            order to fit this grammar it needs to be tighter.
         +  Should "_" (or whatever delimiter) be allowed in the zone
            ID? ("No" complicates the ABNF)




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         +  Can a scoping-arch revision change the character in use? It
            could suggest that "_" can be used as an alternative to "%".
   o  Use %25 as an encoded %, the scoping-arch separator.
      Pro:
         +  "%" is the same character.
      Con:
         +  "%25" is confusing.
         +  Can't copy and paste from other forms where the % is not
            encoded.  (But that is the case also when using a different
            character for the separator.)
         +  IPvFuture ABNF doesn't permit percent-encoded characters.
      Issues:
         +  Would need to change the IPvFuture grammar in URI [RFC3986]
            and IRI [RFC3987] specs to permit percent-encoded
            characters.
   o  Use '%' in the URI
      Pro:
         +  "%" is the same character.
         +  Can copy and paste between forms.
      Con:
         +  '%' is fundamentally special in URIs; parsers can be
            expected to be hard-wired to know that they start a
            percent-encoded octet.
         +  IPvFuture ABNF doesn't permit bare percent.
      Issues:
         +  Impossible to ensure that this exception to a fundamental
            URI rule would be handled properly by parsers.

3.  Limitations

   The usefulness of a URI or IRI using a literal scoped address is
   obviously limited to systems within the same scope.  The addition of
   the zone identifier further limits the usefulness to the system on
   which the URI or IRI was generated, since zone IDs are completely
   local to a given host.  Therefore, care must be taken to not pass
   these URIs blindly between systems.  When both systems are aware of
   the relevant Zone IDs, e.g., an SNMP manager that is aware of the
   zone ID configuration of an agent, it is acceptable to pass these
   URIs between systems.

4.  IANA Considerations

   This document makes no request of IANA.

   Note to RFC Editor: this section may be removed on publication as an
   RFC.





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5.  Security Considerations

   RFC 3986 [RFC3986] describes security considerations for URIs; this
   specification does not add any new security considerations.

6.  Acknowledgements

   Margaret Wasserman first noticed that the original literal IPv6 form
   didn't support zone IDs.  This document was first created based on
   discussions between Steve Bellovin, Brian Carpenter, Roy Fielding,
   Ted Hardie, Larry Masinter, and Thomas Narten.

7.  Normative References

   [RFC2234]  Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
              Specifications: ABNF", RFC 2234, November 1997.

   [RFC3986]  Berners-Lee, T., Fielding, R. and L. Masinter, "Uniform
              Resource Identifier (URI): Generic Syntax", STD 66,
              RFC 3986, January 2005.

   [RFC3987]  Duerst, M. and M. Suignard, "Internationalized Resource
              Identifiers (IRIs)", RFC 3987, January 2005.

   [ipv6-scoping-arch]
              Deering, S., "IPv6 Scoped Address Architecture",
              Internet-Draft draft-ietf-ipv6-scoping-arch-02, August
              2004.


Authors' Addresses

   Bill Fenner
   AT&T Labs -- Research
   75 Willow Rd
   Menlo Park, California  94025
   USA

   Phone: +1 650-330-7893
   Email: fenner@research.att.com











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   Martin Duerst
   World Wide Web Consortium
   5322 Endo
   Fujisawa, Kanagawa  252-8520
   Japan

   Phone: +81 466 49 1170
   Email: duerst@w3.org

Appendix A.  Change History

A.1  Changes since -00

   o  Add "use '%' in the URI" text with pros and cons
   o  Add "Limitations" section




































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