Internet DRAFT - draft-ietf-6man-uri-zoneid
draft-ietf-6man-uri-zoneid
6MAN B. Carpenter
Internet-Draft Univ. of Auckland
Updates: 3986 (if approved) S. Cheshire
Intended status: Standards Track Apple Inc.
Expires: June 10, 2013 R. Hinden
Check Point
December 7, 2012
Representing IPv6 Zone Identifiers in Address Literals and Uniform
Resource Identifiers
draft-ietf-6man-uri-zoneid-06
Abstract
This document describes how the Zone Identifier of an IPv6 scoped
address, as defined in RFC 4007, 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.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
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Internet-Drafts are draft documents valid for a maximum of six months
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This Internet-Draft will expire on June 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
Provisions Relating to IETF Documents
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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 . . . . . . . . . . . . . . . . . . . 6
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 6
7. Change log [RFC Editor: Please remove] . . . . . . . . . . . . 7
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 7
8.1. Normative References . . . . . . . . . . . . . . . . . . . 7
8.2. Informative References . . . . . . . . . . . . . . . . . . 8
Appendix A. Options Considered . . . . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 10
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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 node where they
are defined, often being the same as IPv6 interface names. They are
completely meaningless for any other node. 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 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. The Appendix briefly describes the various options 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. Unfortunately "%" is always treated as an escape character
in a URI, and according to RFC 3986 it MUST therefore itself be
percent-encoded in a URI, in the form "%25". Thus, the scoped
address fe80::a%en1 would appear in a URI as http://[fe80::a%25en1].
A <zone_id> SHOULD contain only ASCII characters classified in RFC
3986 as "unreserved". This excludes characters such as "]" or even
"%" which would complicate parsing. However, the syntax 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 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:
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IP-literal = "[" ( IPv6address / IPv6addrz / IPvFuture ) "]"
ZoneID = 1*( unreserved / pct-encoded )
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 significance
only.
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-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 an unescaped "%"
character, but this was removed for consistency with RFC 3986. As
another example, some 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.
It is desirable for all browsers to recognise a ZoneID preceded by an
escaped "%". 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
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manually escaped as "fe80::a%25ee1" to avoid any risk of
misinterpretation.
Such bare "%" signs are for user interface convenience, and need to
be turned into properly escaped characters (where "%25" encodes "%")
before the URI is used in any protocol or HTML document. However,
URIs including a ZoneID have no meaning outside the originating node.
It would therefore be highly desirable for a browser to remove the
ZoneID from a URI before including that URI in an HTTP request.
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 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 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 remove any ZoneID
attached to an outgoing 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.
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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.
This document was produced using the xml2rfc tool [RFC2629].
7. Change log [RFC Editor: Please remove]
draft-ietf-6man-uri-zoneid-06: responding to IETF Last Call and IESG
comments, 2012-12-07.
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.
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.
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[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.
[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. 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 present solution offers more flexibility for future
uses and is more straightforward to implement.
The various syntax options considered are now briefly described.
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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.
This is the option chosen for standardization.
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.
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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
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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