6MAN B. Carpenter
Internet-Draft Univ. of Auckland
Updates: 3986 (if approved) S. Cheshire
Intended status: Standards Track Apple Inc.
Expires: May 10, 2013 R. Hinden
Check Point
November 6, 2012
Representing IPv6 Zone Identifiers in Address Literals and Uniform
Resource Identifiers
draft-ietf-6man-uri-zoneid-05
Abstract
This document describes how the Zone Identifier of an IPv6 scoped
address can be represented in a literal IPv6 address and in a Uniform
Resource Identifier that includes such a literal address. It updates
RFC 3986 accordingly.
Status of this Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on May 10, 2013.
Copyright Notice
Copyright (c) 2012 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
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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 . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Specification . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Web Browsers . . . . . . . . . . . . . . . . . . . . . . . . . 5
4. Security Considerations . . . . . . . . . . . . . . . . . . . . 5
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 6
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 6
7. Change log [RFC Editor: Please remove] . . . . . . . . . . . . 6
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 7
8.1. Normative References . . . . . . . . . . . . . . . . . . . 7
8.2. Informative References . . . . . . . . . . . . . . . . . . 7
Appendix A. Alternatives Considered . . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 9
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1. Introduction
The Uniform Resource Identifier (URI) syntax [RFC3986] defined how a
literal IPv6 address can be represented in the "host" part of a URI.
A subsequent 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
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 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, 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 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.
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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 [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". Thus, the scoped address fe80::a%en1 would
appear in a URI as http://[fe80::a%25en1].
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 = "[" ( IPv6address / IPv6addrz / IPvFuture ) "]"
ZoneID = 1*( unreserved / pct-encoded )
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IPv6addrz = IPv6address "%25" ZoneID
This syntax fills the gap that is described at the end of Section
11.7 of RFC 4007.
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
only.
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.
This document implies that all browsers should recognise a ZoneID
preceded by an escaped "%". In the spirit of "be liberal with what
you accept", we also recommend that URI parsers accept bare "%" signs
(i.e., a "%" not followed by two valid hexadecimal characters). This
makes it easy 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.
4. Security Considerations
The security considerations of [RFC3986] and [RFC4007] apply. In
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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.
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, Ted Hardie, 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-05: tuned ABNF, clarified RFC 4007 text,
2012-11-06.
draft-ietf-6man-uri-zoneid-04: additional author, 2012-09-21.
draft-ietf-6man-uri-zoneid-03: reverted to percent-encoded model
following WGLC, 2012-09-10.
draft-ietf-6man-uri-zoneid-02: additional WG comments, 2012-07-11.
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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
[I-D.fenner-literal-zone]
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.
[I-D.iab-identifier-comparison]
Thaler, D., "Issues in Identifier Comparison for Security
Purposes", draft-iab-identifier-comparison-03 (work in
progress), July 2012.
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[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://
support.google.com/chrome/bin/answer.py?answer=95440>.
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.
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. Escaping the escape character as allowed by 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.
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4. Alternative separator
http://[fe80::a-en1]
Advantage: allows use of browser, simple syntax
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.
5. With the "IPvFuture" syntax left open in RFC 3986:
http://[v6.fe80::a_en1]
Advantage: allows use of browser.
Disadvantage: ugly and redundant, doesn't allow simple cut and
paste.
Authors' Addresses
Brian Carpenter
Department of Computer Science
University of Auckland
PB 92019
Auckland, 1142
New Zealand
Email: brian.e.carpenter@gmail.com
Stuart Cheshire
Apple Inc.
1 Infinite Loop
Cupertino, CA 95014
US
Email: cheshire@apple.com
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Robert M. Hinden
Check Point Software Technologies, Inc.
800 Bridge Parkway
Redwood City, CA 94065
US
Email: bob.hinden@gmail.com
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