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Versions: 00 01

Internet Engineering Task Force                            M. Sweet, Ed.
Internet-Draft                                                Apple Inc.
Intended status: Standards Track                            B. Carpenter
Expires: February 28, 2014                        University of Auckland
                                                             S. Cheshire
                                                              Apple Inc.
                                                               R. Hinden
                                 Check Point Software Technologies, Inc.
                                                         August 27, 2013


   Representing IPv6 Zone Identifiers in Address Literals and Uniform
                          Resource Identifiers
                       draft-sweet-uri-zoneid-00

Abstract

   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
   updates the URI Generic Syntax specification (RFC 3986) accordingly.

   [ Editor's note: This draft adds the IPvFuture format used by CUPS
   since 2005, addresses some misconceptions of how zoneid's are not
   useful to HTTP servers, and is intended to replace 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
   Task Force (IETF).  Note that other groups may also distribute
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   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
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   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on February 28, 2014.

Copyright Notice

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



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   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
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   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 . . . . . . . . . . . . . . . . . .   3
   2.  Specification . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Web Browsers  . . . . . . . . . . . . . . . . . . . . . . . .   5
   4.  Security Consideration  . . . . . . . . . . . . . . . . . . .   6
   5.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   7
   6.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   7
     6.1.  Normative References  . . . . . . . . . . . . . . . . . .   7
     6.2.  Informative References  . . . . . . . . . . . . . . . . .   7
   Appendix A.  Options Considered . . . . . . . . . . . . . . . . .   8
   Appendix B.  Change History . . . . . . . . . . . . . . . . . . .   9
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  10

1.  Introduction

   The Uniform Resource Identifier (URI) syntax specification [RFC3986]
   defined how a literal IPv6 address can be represented in the "host"
   part of a URI.  Two months later, the IPv6 Scoped Address
   Architecture specification [RFC4007] extended the text representation
   of limited-scope IPv6 addresses such that a zone identifier may be
   concatenated to a literal address, for purposes described in that
   specification.  Zone identifiers are especially useful in contexts in
   which literal addresses are typically used, for example, during fault
   diagnosis, when it may be essential to specify which interface is
   used for sending to a link-local address.  It should be noted that
   zone identifiers have purely local meaning within the node in which
   they are defined, often being the same as IPv6 interface names.  They
   are completely meaningless for any other node.  Today, they are
   meaningful only when attached to addresses with less than global
   scope, but it is possible that other uses might be defined in the
   future.

   The IPv6 Scoped Address Architecture specification [RFC4007] does not
   specify how zone identifiers are to be represented in URIs.
   Practical experience has shown that this feature is useful, in
   particular when using a web browser for debugging with link-local



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   addresses, but because it is undefined, it is not implemented
   consistently in URI parsers or in browsers.

   Some versions of some browsers directly accept the IPv6 Scoped
   Address syntax [RFC4007] for scoped IPv6 addresses embedded in URIs,
   i.e., they have been coded to interpret a "%" sign following the
   literal address as introducing a zone identifier [RFC4007], instead
   of introducing two hexadecimal characters representing some percent-
   encoded octet [RFC3986].  Clearly, interpreting the "%" sign as
   introducing a zone identifier is very convenient for users, although
   it formally breaches the established URI syntax [RFC3986].  This
   document defines an alternative approach that respects and extends
   the rules of URI syntax, and IPv6 literals in general, to be
   consistent.

   Thus, this document updates the URI syntax specification [RFC3986] by
   adding two syntaxes that allow a zone identifier to be included in a
   literal IPv6 address within a URI.  The first extends the ABNF
   [RFC5234] syntax to allow for a direct inclusion of the zone ID while
   the second is backwards-compatible with the original syntax defined
   in RFC 3986.

   It should be noted that in contexts other than a user interface, a
   zone identifier is mapped into a numeric zone index or interface
   number.  The MIB textual convention InetZoneIndex [RFC4001] and the
   socket interface [RFC3493] define this as a 32-bit unsigned integer.
   The mapping between the human-readable zone identifier string and the
   numeric value is a host-specific function that varies between
   operating systems.  The present document is concerned only with the
   human-readable string.

   Several alternative solutions were considered while this document was
   developed.  Appendix A briefly describes the various options and
   their advantages and disadvantages.

1.1.  Requirements Language

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

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



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   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://
   [fe80::a%25en1].

   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].  Note: This format, originally
   proposed in 2005, was adopted by CUPS [CUPS] and has subsequently
   become widely implemented for printing.

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

   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 / IPv6addrz / IPvFuture  ) "]"

   ZoneID = 1*( unreserved / pct-encoded )

   IPv6addrz = IPv6address "%25" ZoneID / "v1." IPv6address "+" ZoneID


   This syntax fills the gap that is described at the end of
   Section 11.7 of the IPv6 Scoped Address Architecture specification
   [RFC4007].

   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
   undefined.

3.  Web Browsers

   This section discusses how web browsers might handle this syntax
   extension.  Unfortunately, there is no formal distinction between the
   syntax allowed in a browser's input dialogue box and the syntax
   allowed in URIs.  For this reason, no normative statements are made
   in this section.

   Due to the lack of defined syntax, web browsers have been
   inconsistent in providing for ZoneIDs.  Many have no support, but
   there are examples of ad hoc support.  For example, some versions of
   Firefox allowed the use of a ZoneID preceded by a bare "%" character,
   but this feature was removed for consistency with established syntax
   [RFC3986].  As another example, some versions of Internet Explorer
   allow use of a ZoneID preceded by a "%" character encoded as "%25",
   still beyond the syntax allowed by the established rules [RFC3986].
   This syntax extension is in fact used internally in the Windows
   operating system and some of its APIs.



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   It is desirable for all browsers to recognise a ZoneID preceded by a
   percent-encoded "%".  In the spirit of "be liberal with what you
   accept", we also suggest that URI parsers accept bare "%" signs when
   possible (i.e., a "%" not followed by two valid and meaningful
   hexadecimal characters).  This would make it possible for a user to
   copy and paste a string such as "fe80::a%en1" from the output of a
   "ping" command and have it work.  On the other hand, "%ee1" would
   need to be manually rewritten to "fe80::a%25ee1" to avoid any risk of
   misinterpretation.

   Such bare "%" signs are for user interface convenience, and need to
   be turned into properly encoded characters (where "%25" encodes "%")
   before the URI is used in any protocol or HTML document.  And while
   URIs including a ZoneID have no meaning outside the originating node,
   the address values can be used to construct subsequent valid URIs on
   behalf of the originating node.  It is therefore highly desirable for
   a browser to retain the ZoneID in any URI included in an HTTP
   request.

   [ Editor's note: Reworded the previous paragraph from RFC 6874 to
   indicate a preference for including the ZoneID. ]

   The normal diagnostic usage for the ZoneID syntax will cause it to be
   entered in the browser's input dialogue box.  Thus, URIs including a
   ZoneID are unlikely to be encountered in HTML documents.  However, if
   they do (for example, in a diagnostic script coded in HTML), it would
   be appropriate to treat them exactly as above.

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 debugging 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.

   An HTTP client, proxy, or other intermediary MUST NOT remove any
   ZoneID attached to an outgoing URI so that URIs generated by the
   receiving host for the sending host retain the sending host's ZoneID
   information



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   [ Editor's note: The previous paragraph has the opposite conformance
   requirement from RFC 6874. ]

5.  Acknowledgements

   The lack of this format was first pointed out by Margaret Wasserman
   some years ago, and more recently by Kerry Lynn.  A previous draft
   document by Martin Duerst and Bill Fenner [LITERAL-ZONE] discussed
   this topic but was not finalised.

   Valuable comments and contributions were made by Karl Auer, Carsten
   Bormann, Benoit Claise, Stephen Farrell, Brian Haberman, Ted Hardie,
   Tatuya Jinmei, Yves Lafon, Barry Leiba, Radia Perlman, Tom Petch,
   Tomoyuki Sahara, Juergen Schoenwaelder, Dave Thaler, Martin Thomson,
   and Ole Troan.

   Brian Carpenter was a visitor at the Computer Laboratory, Cambridge
   University during part of this work.

6.  References

6.1.  Normative References

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

   [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.

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

6.2.  Informative References

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

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




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   [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.

Appendix A.  Options Considered

   The syntax defined above allows a ZoneID to be added to any IPv6
   address.  The 6man WG discussed and rejected an alternative in which
   the existing syntax of IPv6address would be extended by an option to
   add the ZoneID only for the case of link-local addresses.  It was
   felt that the solution presented in this document offers more
   flexibility for future uses and is more straightforward to implement.

   The various syntax options considered are now briefly described.

   [ Editor's note: I reversed items 4 and 5 from RFC 6874 and adjusted
   the example to match the alternate syntax used in CUPS. ]

   1. Leave the problem unsolved.

      This would mean that per-interface diagnostics would still have to
      be performed using ping or ping6:

      ping fe80::a%en1

      Advantage: works today.

      Disadvantage: less convenient than using a browser.

   2. Simply use the percent character:

      http://[fe80::a%en1]

      Advantage: allows use of browser; allows cut and paste.

      Disadvantage: invalid syntax under RFC 3986; not acceptable to URI
      community.

   3. Simply use an alternative separator:

      http://[fe80::a-en1]

      Advantage: allows use of browser; simple syntax.




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      Disadvantage: Requires all IPv6 address literal parsers and
      generators to be updated in order to allow simple cut and paste;
      inconsistent with existing tools and practice.

      Note: The initial proposal for this choice was to use an
      underscore as the separator, but it was noted that this becomes
      effectively invisible when a user interface automatically
      underlines URLs.

   4. Retain the percent character already specified for introducing
      zone identifiers for IPv6 Scoped Addresses [RFC4007], and then
      percent-encode it when it appears in a URI, according to the
      already-established URI syntax rules [RFC 3986]:

      http://[fe80::a%25en1]

      Advantage: allows use of browser; consistent with general URI
      syntax.

      Disadvantage: somewhat ugly and confusing; doesn't allow simple
      cut and paste.

      This is the primary format chosen for standardization.

   5. Simply use the "IPvFuture" syntax left open in RFC 3986:

      http://[v1.fe80::a+en1]

      Advantage: allows use of browser, compatible with RFC 3986-based
      URI parsers.

      Disadvantage: ugly; doesn't allow simple cut and paste.

      This is the alternate format chosen for standardization.

Appendix B.  Change History

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

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

   [ Changes are from published RFC 6874 text ]

   o  Abstract: Added editor's note explaining why we need to update RFC
      6874

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




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   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.

Authors' Addresses

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

   Email: msweet@apple.com


   Brian Carpenter
   University of Auckland
   Department of Computer Science
   Auckland, PB 92019  1142
   New Zealand

   Email: brian.e.carpenter@gmail.com


   Stuart Cheshire
   Apple Inc.
   1 Infinite Loop
   Cupertino, California  95014
   United States

   Email: cheshire@apple.com











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   Robert M. Hinden
   Check Point Software Technologies, Inc.
   800 Bridge Parkway
   Redwood City, California  94065
   United States

   Email: bob.hinden@gmail.com












































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