6MAN                                                        B. Carpenter
Internet-Draft                                         Univ. of Auckland
Updates: 3986, 4007 (if approved)                              R. Hinden
Intended status: Standards Track                             Check Point
Expires: November 30, 2012                                  May 29, January 12, 2013                                  July 11, 2012

   Representing IPv6 Zone Identifiers in Address Literals and Uniform
                          Resource Identifiers


   This document describes how the Zone Identifier of an IPv6 scoped
   address can be represented in a a literal IPv6 address and in a
   Uniform Resource Identifier that includes such a literal IPv6 address.  It
   updates RFC 3986 and RFC 4007. 4007 accordingly.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . . 3
   2.  Specification . . . . . . . . . . . . . . . . . . . . . . . . . 4
   3.  Web Browsers  . . . . . . . . . . . . . . . . . . . . . . . . . 5
   4.  Security Considerations . . . . . . . . . . . . . . . . . . . . 5 6
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 6
   6.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . 6
   7.  Change log [RFC Editor: Please remove]  . . . . . . . . . . . . 6 7
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . . . 7
     8.1.  Normative References  . . . . . . . . . . . . . . . . . . . 7
     8.2.  Informative References  . . . . . . . . . . . . . . . . . . 7 8
   Appendix A.  Alternatives Considered  . . . . . . . . . . . . . . . 7 8
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . . . 9

1.  Introduction

   [RFC3986] defined how a literal IPv6 address can be represented in
   the "host" part of a Uniform Resource Identifier (URI).
   Subsequently, [RFC4007] extended the text representation of limited-
   scope IPv6 addresses such that a zone identifier may be concatenated
   to an a literal address, for purposes described in that RFC.  Zone
   identifiers are especially useful in contexts where 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 host where they are defined, and they are
   completely meaningless for any other host.  Today, they are only
   meaningful when attached to addresses with link local less than global scope,
   but it is possible that other uses might be defined in the future.

   RFC 4007 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
   addresses, but as it is undefined, it is not implemented consistently
   in URI parsers or in browsers.

   Some versions of some browsers accept the RFC 4007 syntax for scoped
   IPv6 addresses embedded in URIs, i.e., they have been coded to
   interpret the "%" sign according to RFC 4007 instead of RFC 3986.
   Clearly this approach is very convenient for users, although it
   formally breaches the syntax rules of RFC 3986.  The present document
   defines an alternative approach that respects and extends the rules
   of URI syntax. syntax, and IPv6 literals in general, to be consistent.

   Thus, this document updates [RFC3986] by adding syntax to allow a
   zone identifier to be included in a literal IPv6 address within a
   URI.  It also clarifies some statements updates [RFC4007], in [RFC4007]. particular by adding a second
   allowed delimiter for zone identifiers.

   It should be noted that in other contexts than a user interface, a
   zone identifier is mapped into a numeric zone index or interface
   number.  The MIB textual convention [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.  The Appendix briefly describes the alternatives and their
   advantages and disadvantages.

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in [RFC2119].

2.  Specification

   According to RFC 4007, 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, RFC 4007 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.  A <zone_id> SHOULD contain only ASCII characters classified
   in RFC 3986 as "unreserved", which conveniently excludes "]" in order
   to simplify parsing.

   Unfortunately "%" is always treated as an escape character in a URI,
   and according to RFC 3986 it MUST therefore itself be escaped in a
   URI, in the form "%25".  For this reason, "-" (hyphen) is used
   instead as the separator when a <zone_id> is included in a URI.
   Thus, the scoped address fe80::a%en1 would appear in a URI as

   If an operating system uses any other characters in zone or interface
   identifiers that are not in the "unreserved" character set, they MUST
   be escaped with a "%" sign according to RFC 3986.

   We now present the necessary formal syntax.

   In RFC 3986, the IPv6 literal format is formally defined 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
   optionally to any literal address.  This allows flexibility for
   unknown future uses.  The rule quoted above from RFC 3986 is replaced
   by three rules:

      IP-literal = "[" ( IPv6addrz / IPvFuture  ) "]"

      ZoneID = 1*( unreserved / pct-encoded )

      IPv6addrz = IPv6address [ "-" ZoneID ]

   Section 11 of RFC 4007 is updated to allow "-" as well as "%" as the
   preceding delimiter of a ZoneID.

   The rules in [RFC5952] SHOULD be applied in producing URIs.

   RFC 3986 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 where they originate, since the ZoneID is of local signifance

   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 present solution offers more flexibility for future uses and
   is more straightforward to implement.

   RFC 4007 offers guidance on how the ZoneID affects interface/address
   selection inside the IPv6 stack.  Note that the behaviour of an IPv6
   stack if passed a non-zero zone index for an address other than link-
   local is undefined.

3.  Web Browsers

   Due to the lack of a standard in this area, web browsers have been
   inconsistent in providing for ZoneIDs.  Many have no support, but
   there are examples of ad hoc support.  For example, older versions of
   Firefox allowed the use of a ZoneID preceded by an unescaped "%"
   character, but this was removed for consistency with RFC 3986.  As
   another example, recent versions of Internet Explorer allow use of a
   ZoneID preceded by a "%" character escaped as "%25", still beyond the
   syntax allowed by RFC 3986.  This syntax extension is in fact used
   internally in the Windows operating system and some of its APIs.

   In recent years, web browsers have evolved considerably and now
   accept and parse many forms of input that are not a formal URI.
   Examples of this include host names, search items, bookmarks, search
   history, etc.  For example the Google Chrome browser now calls the
   "address bar" the "omnibox" [chrome].  The authors believe it is
   feasible, and very convenient for users, if browsers also allow (in
   addition to the formal URI syntax defined in this document) a syntax
   that will enable cut and paste.  For example:


   It seems that modern browsers can be adapted to parse this because it
   is inside of the "[" "]"'s.  This would permit the output of commands
   like ping6 -w ff02::1%en1 to be "cut and pasted" into a browser
   address bar.  Consequently this document recommends that browsers
   support this syntax in addition to the formal URI syntax defined

4.  Security Considerations

   The security considerations of [RFC3986] and [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 RFC 4007.  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 SHOULD NOT allow use of this
   format except for well-defined usages such as sending to link local
   addresses under prefix fe80::/10.

   An HTTP server or proxy MUST ignore any ZoneID attached to an
   incoming URI, as it only has local significance at the sending host.

   The addition of a choice between "%" and "-" as the delimiter
   preceding a ZoneID slightly complicates the string comparison issue
   discussed in [I-D.iab-identifier-comparison].

5.  IANA Considerations

   This document requests no action by IANA.

6.  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 [I-D.fenner-literal-zone]
   discussed this topic but was not finalised.

   Valuable comments and contributions were made by Karl Auer, Carsten
   Bormann, Brian Haberman, Tatuya Jinmei, Tom Petch, Tomoyuki Sahara,
   Juergen Schoenwaelder, Dave Thaler, and Ole Troan.

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

   This document was produced using the xml2rfc tool [RFC2629].

7.  Change log [RFC Editor: Please remove]

   draft-ietf-6man-uri-zoneid-02: additional WG comments, 2012-07-11.

   draft-ietf-6man-uri-zoneid-01: use "-" instead of %25, listed
   alternatives in Appendix, according to WG debate, added suggestion
   for browser developers, 2012-05-29.

   draft-ietf-6man-uri-zoneid-00: adopted by WG, fixed syntax to allow
   for % encoded characters, 2012-02-17.

   draft-carpenter-6man-uri-zoneid-01: chose Option 2, removed 15
   character limit, added explanation of ID/number mapping and other
   clarifications, 2012-02-08.

   draft-carpenter-6man-uri-zoneid-00: original version, 2011-12-07.

8.  References

8.1.  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.

8.2.  Informative References

              Fenner, B. and M. Duerst, "Formats for IPv6 Scope Zone
              Identifiers in Literal Address Formats",
              draft-fenner-literal-zone-02 (work in progress),
              October 2005.

              Thaler, D., "Issues in Identifier Comparison for Security
              Purposes", draft-iab-identifier-comparison-02 (work in
              progress), May 2012.

   [RFC2629]  Rose, M., "Writing I-Ds and RFCs using XML", RFC 2629,
              June 1999.

   [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.

   [chrome]   Google, "Use the address bar (omnibox)", 2012, <http://

Appendix A.  Alternatives Considered

   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 using the percent character.


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

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

   3.  Escaping the escape character as allowed by RFC 3986:


       Advantage: allows use of browser.

       Disadvantage: ugly and confusing, doesn't allow simple cut and

   4.  Alternative separator


       Advantage: allows use of browser, simple syntax

       Disadvantage: doesn't Requires all IPv6 address literal parsers and
       generators to be updated in order to allow simple cut and paste.

       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.

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


       Advantage: allows use of browser.

       Disadvantage: ugly and redundant, doesn't allow simple cut and

Authors' Addresses

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

   Email: brian.e.carpenter@gmail.com
   Robert M. Hinden
   Check Point Software Technologies, Inc.
   800 Bridge Parkway
   Redwood City, CA  94065

   Email: bob.hinden@gmail.com