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Versions: 00 01

Internet Engineering Task Force                            M. Sweet, Ed.
Internet-Draft                                                Apple Inc.
Intended status: Informational                         November 22, 2013
Expires: May 26, 2014

           An IPvFuture Syntax for IPv6 Link-Local Addresses


   This document describes how the zone identifier of an IPv6 scoped
   address, defined as <zone_id> in the IPv6 Scoped Address Architecture
   (RFC 4007), can be represented in a literal IPv6 address and in a
   Uniform Resource Identifier that includes such a literal address.  It
   documents a long-standing usage of the IPvFuture extension point
   provided in the Uniform Resource Identifier (URI) syntax
   specification [RFC3986].

   [ Editor's note: This draft documents the IPvFuture format originally
   defined in [LITERAL-ZONE] and used by CUPS since 2005.  A separate,
   incompatible format was defined and published in RFC 6874. ]

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
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   This Internet-Draft will expire on May 26, 2014.

Copyright Notice

   Copyright (c) 2013 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of

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   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
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   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Requirements Language . . . . . . . . . . . . . . . . . .   2
   2.  Specification . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  HTTP Requirements . . . . . . . . . . . . . . . . . . . . . .   4
   4.  Security Consideration  . . . . . . . . . . . . . . . . . . .   5
   5.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   5
     5.1.  Normative References  . . . . . . . . . . . . . . . . . .   5
     5.2.  Informative References  . . . . . . . . . . . . . . . . .   6
   Appendix A.  Change History . . . . . . . . . . . . . . . . . . .   6
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   7

1.  Introduction

   The Uniform Resource Identifier (URI) syntax specification [RFC3986]
   defines how a literal IPv6 address can be represented in the "host"
   part of a URI.  However, it does not define how zone identifiers (see
   IPv6 Scoped Address Architecture specification [RFC4007]) are
   represented, which has lead to the development and deployment of two
   incompatible URI syntax extensions.  The first syntax, "A Format for
   IPv6 Scope Zone Identifiers in Literal URIs" [LITERAL-ZONE], was
   originally proposed in 2005 and used the IPvFuture rule that was
   defined for future address extensions in URIs.  While this draft was
   ultimately never published, the syntax was adopted by the CUPS [CUPS]
   software in 2005 and is now widely deployed in clients and printers.
   The second syntax, "Representing IPv6 Zone Identifiers in Address
   Literals and Uniform Resource Identifiers" [RFC6874], was published
   in February 2013 and incompatibly extends the URI syntax with a new
   IPv6addrz rule.  This document describes the first syntax and
   provides additional implementation guidelines for its use.

   [ Editor's note: Would it be appropriate to provide adoption numbers
   here (hundreds of millions of devices)? ]

1.1.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in "Key words for use in
   RFCs to Indicate Requirement Levels" [RFC2119].

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2.  Specification

   According to IPv6 Scoped Address syntax [RFC4007], a zone identifier
   is attached to the textual representation of an IPv6 address by
   concatenating "%" followed by <zone_id>, where <zone_id> is a string
   identifying the zone of the address.  However, the IPv6 Scoped
   Address Architecture specification gives no precise definition of the
   character set allowed in <zone_id>.  There are no rules or de facto
   standards for this.  For example, the first Ethernet interface in a
   host might be called %0, %1, %en1, %eth0, or whatever the implementer
   happened to choose.

   In a URI, a literal IPv6 address is always embedded between "[" and
   "]".  This document specifies how a <zone_id> can be appended to the
   address.  According to URI syntax [RFC3986], "%" is always treated as
   an escape character in a URI, so, according to the established URI
   syntax [RFC3986] any occurrences of literal "%" symbols in a URI MUST
   be percent-encoded and represented in the form "%25".  Thus, the
   scoped address fe80::a%en1 would appear in a URI as http://

   However, since parsers based on the ABNF [RFC5234] in the URI syntax
   specification [RFC3986] will not allow a URI of that form, an
   alternate format based on the IPvFuture rule [LITERAL-ZONE] can be
   used where the address is prefixed with "v1." and the "+" character
   is used as the separator between the address and <zone_id>.  Thus,
   the alternate form of the scoped address fe80::a%en1 would appear in
   a URI as http://[v1.fe80::a+en1].

   A <zone_id> SHOULD contain only ASCII characters classified as
   "unreserved" for use in URIs [RFC3986].  This excludes characters
   such as "]" or even "%" that would complicate parsing.  However, the
   syntax described below does allow such characters to be percent-
   encoded, for compatibility with existing devices that use them.

   If an operating system uses any other characters in zone or interface
   identifiers that are not in the "unreserved" character set, they MUST
   be represented using percent encoding [RFC3986].

   We now present the necessary formal syntax.

   The URI syntax specification [RFC3986] formally defined the IPv6
   literal format in ABNF [RFC5234] by the following rule:

   IP-literal = "[" ( IPv6address / IPvFuture  ) "]"

   To provide support for a zone identifier, the existing syntax of
   IPv6address is retained, and a zone identifier may be added

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   optionally to any literal address.  This syntax allows flexibility
   for unknown future uses.  The rule quoted above from the previous URI
   syntax specification [RFC3986] is replaced by three rules:

   IP-literal = "[" ( IPv6address / IPvFuture /
                      "v1." IPv6address "+" ZoneID ) "]"

   ZoneID = 1*( unreserved / pct-encoded )

   This syntax fills the gap that is described at the end of
   Section 11.7 of the IPv6 Scoped Address Architecture specification

   The established rules for textual representation of IPv6 addresses
   [RFC5952] SHOULD be applied in producing URIs.

   The URI syntax specification [RFC3986] states that URIs have a global
   scope, but that in some cases their interpretation depends on the
   end-user's context.  URIs including a ZoneID are to be interpreted
   only in the context of the host at which they originate, since the
   ZoneID is of local significance only.

   The IPv6 Scoped Address Architecture specification [RFC4007] offers
   guidance on how the ZoneID affects interface/address selection inside
   the IPv6 stack.  Note that the behaviour of an IPv6 stack, if it is
   passed a non-null zone index for an address other than link-local, is

3.  HTTP Requirements

   The Hypertext Transfer Protocol -- HTTP/1.1 [RFC2616] requires the
   client to supply the host and URI used to access the server.  While a
   ZoneID is only significant to the HTTP client, many HTTP server
   solutions, including IPP [RFC2911], generate absolute URIs to server-
   resident resources in response to a client's request.  If the
   client's ZoneID is not sent to the server, the server will not be
   able to provide absolute URIs that can be directly used by the
   client.  However, the server cannot use the provided ZoneID for any
   local address comparisons since the client and server likely have
   different ZoneID's for the same IPv6 link-local address.

   HTTP clients SHOULD include the client-specific ZoneID in the HTTP
   Host: header and (if applicable) the HTTP Request-URI.

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   HTTP servers MUST support Host: and Request-URI values containing
   client-specific ZoneID's, MUST use the full address (including
   ZoneID) when generating absolute URIs for a response to the client,
   and MUST NOT use the ZoneID in any local (server) address

4.  Security Consideration

   The security considerations from the URI syntax specification
   [RFC3986] and the IPv6 Scoped Address Architecture specification
   [RFC4007] apply.  In particular, this URI format creates a specific
   pathway by which a deceitful zone index might be communicated, as
   mentioned in the final security consideration of the Scoped Address
   Architecture specification.  It is emphasised that the format is
   intended only for local access purposes, but of course this intention
   does not prevent misuse.

   To limit this risk, implementations MUST NOT allow use of this format
   except for well-defined usages, such as sending to link-local
   addresses under prefix fe80::/10.  At the time of writing, this is
   the only well-defined usage known.

5.  References

5.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC2616]  Fielding, R., Gettys, J., Mogul, J., Frystyk, H.,
              Masinter, L., Leach, P., and T. Berners-Lee, "Hypertext
              Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999.

   [RFC2911]  Hastings, T., Herriot, R., deBry, R., Isaacson, S., and P.
              Powell, "Internet Printing Protocol/1.1: Model and
              Semantics", RFC 2911, September 2000.

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

   [RFC4007]  Deering, S., Haberman, B., Jinmei, T., Nordmark, E., and
              B. Zill, "IPv6 Scoped Address Architecture", RFC 4007,
              March 2005.

   [RFC5234]  Crocker, D. and P. Overell, "Augmented BNF for Syntax
              Specifications: ABNF", STD 68, RFC 5234, January 2008.

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   [RFC5952]  Kawamura, S. and M. Kawashima, "A Recommendation for IPv6
              Address Text Representation", RFC 5952, August 2010.

5.2.  Informative References

   [CUPS]     Sweet, M., "CUPS software", October 2005.

              Fenner, B. and M. Duerst, "A Format for IPv6 Scope Zone
              Identifiers in Literal URIs", October 2005.

   [RFC3493]  Gilligan, R., Thomson, S., Bound, J., McCann, J., and W.
              Stevens, "Basic Socket Interface Extensions for IPv6", RFC
              3493, February 2003.

   [RFC4001]  Daniele, M., Haberman, B., Routhier, S., and J.
              Schoenwaelder, "Textual Conventions for Internet Network
              Addresses", RFC 4001, February 2005.

   [RFC6874]  Carpenter, B., Cheshire, S., and R. Hinden, "Representing
              IPv6 Zone Identifiers in Address Literals and Uniform
              Resource Identifiers", RFC 6874, February 2013.

Appendix A.  Change History

   [ RFC Editor: This section to be deleted before RFC publication ]

   November 22, 2013 - draft-sweet-uri-zoneid-01

   o  Changed to informative draft to document what CUPS has been using
      since 2005.

   o  Section 1: Rewritten to document the two incompatible syntaxes.

   o  Section 2: Dropped 6874 syntax and added the v1. syntax to the
      main address rule.

   o  Section 3: Changed to HTTP Requirements, explained why this is
      necessary, provided conformance requirements.

   o  Section 4: Cleaned up now that we are no longer obsoleting 6874.

   o  Deleted unused sections/appendices

   August 27, 2013 - draft-sweet-uri-zoneid-00

   [ Changes are from published RFC 6874 text ]

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   o  Abstract: Added editor's note explaining why we need to update RFC

   o  Section 1: Update to talk about having two formats.

   o  Section 2: Provide example and define IPvFuture format as an
      alternate, RFC 3986-compatible encoding.

   o  Section 3: Reword to encourage browsers to retain the ZoneID as an
      aid for getting usable server-generated URIs.

   o  Section 4: Change conformance to MUST NOT remove ZoneID.

   o  Section 6.2: Add reference to CUPS.

   o  Appendix A: Put the IPvFuture example at the end, make it match
      the correct IPvFuture format, and note it at the alternate syntax.

Author's Address

   Michael Sweet (editor)
   Apple Inc.
   1 Infinite Loop
   Cupertino, California  95014
   United States

   Email: msweet@apple.com

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