wdiff rfc6874.original rfc6874.txt

6MAN
Internet Engineering Task Force (IETF) B. Carpenter
Internet-Draft
Request for Comments: 6874 Univ. of Auckland
Updates: 3986 (if approved) S. Cheshire
Intended status:
Category: Standards Track Apple Inc.
Expires: June 10, 2013
ISSN: 2070-1721 R. Hinden
Check Point
December 7, 2012
February 2013

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 zone identifier of an IPv6 scoped
address, as defined as <zone_id> in RFC 4007, 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 RFC 3986 the URI Generic Syntax specification (RFC 3986) accordingly.

Status of this 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 June 10, 2013.
http://www.rfc-editor.org/info/rfc6874.

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Table of Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 2
2. Specification . . . . . . . . . . . . . . . . . . . . . . . . 4 . 3
3. Web Browsers . . . . . . . . . . . . . . . . . . . . . . . . . 5
4. Security Considerations . . . . . . . . . . . . . . . . . . . 6
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
6.
5. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 6
7. Change log [RFC Editor: Please remove] . . . . . . . . . . . . 7
8.
6. References . . . . . . . . . . . . . . . . . . . . . . . . . . 7
8.1.
6.1. Normative References . . . . . . . . . . . . . . . . . . . 7
8.2.
6.2. Informative References . . . . . . . . . . . . . . . . . . 8 7
Appendix A. Options Considered . . . . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 10 8

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.
A subsequent 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
RFC.
specification. Zone identifiers are especially useful in contexts where in
which literal addresses are typically used, for example example, during fault
diagnosis, when it may be essential to specify which interface is
used for sending to a link local link-local address. It should be noted that
zone identifiers have purely local meaning within the node where in which
they are defined, often being the same as IPv6 interface names. They
are completely meaningless for any other node. Today, they are only
meaningful only when attached to addresses with less than global
scope, but it is possible that other uses might be defined in the
future.

RFC 4007

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

Some versions of some browsers directly accept the RFC 4007 IPv6 Scoped
Address syntax [RFC4007] for scoped IPv6 addresses embedded in URIs,
i.e., they have been coded to interpret the a "%" sign according to RFC 4007 following the
literal address as introducing a zone identifier [RFC4007], instead
of RFC 3986.
Clearly this approach 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 rules of RFC 3986. The present [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 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 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 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 A briefly describes the various options and
their advantages and disadvantages.

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 RFC 4007, 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, RFC 4007 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. Unfortunately According to URI syntax [RFC3986], "%" is always treated as
an escape character in a URI, and so, according to RFC 3986 it the established URI
syntax [RFC3986] any occurrences of literal "%" symbols in a URI MUST therefore itself
be percent-encoded in a URI, and represented 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".
"unreserved" for use in URIs [RFC3986]. This excludes characters
such as "]" or even "%" which that would complicate parsing. However, the
syntax described below does allow such characters to be percent-encoded, 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. represented using percent encoding [RFC3986].

We now present the necessary formal syntax.

In RFC 3986,

The URI syntax specification [RFC3986] formally defined 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 syntax allows flexibility
for unknown future uses. The rule quoted above from RFC 3986 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

This syntax fills the gap that is described at the end of Section
11.7 of RFC 4007. the IPv6 Scoped Address Architecture specification [RFC4007].

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

RFC 3986

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 where at which they originate, since the
ZoneID is of local significance only.

RFC 4007

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 stack, if it is
passed a non-null zone index for an address other than link-
local link-local, is
undefined.

3. Web Browsers

This section discusses how web browsers might handle this syntax
extension. Unfortunately 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 a bare "%" character,
but this feature was removed for consistency with RFC 3986. established syntax
[RFC3986]. As another example, some versions of Internet Explorer
allow use of a ZoneID preceded by a "%" character escaped encoded as "%25",
still beyond the syntax allowed by RFC 3986. the established rules [RFC3986].
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 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 escaped as 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 escaped encoded 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) HTML), it would
be appropriate to treat them exactly as above.

4. Security Considerations

The security considerations of 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 RFC 4007. 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 usages, such as sending to link local link-local
addresses under prefix fe80::/10. At the time of writing, this is
the only well-defined usage known.

An HTTP client, proxy proxy, or other intermediary MUST remove any ZoneID
attached to an outgoing URI, as it only has only 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] [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.

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.

6. References

8.1.

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. D., Ed. 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.

6.2. Informative References

[I-D.fenner-literal-zone]

[LITERAL-ZONE] Fenner, B. and M. Duerst, "Formats for IPv6 Scope
Zone Identifiers in Literal Address Formats",
draft-fenner-literal-zone-02 (work Work
in progress), 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 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.

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 use the percent character. character:

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

Advantage: allows use of browser, 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 Simply 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 an alternative separator:

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

Advantage: allows use of browser, browser; simple syntax 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 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

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

http://[v6.fe80::a_en1]

Advantage: allows use of browser.

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

5. 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 option chosen for standardisation.

Authors' Addresses

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

Email:

EMail: brian.e.carpenter@gmail.com

Stuart Cheshire
Apple Inc.
1 Infinite Loop
Cupertino, CA 95014
US

Email:
United States

EMail: cheshire@apple.com

Robert M. Hinden
Check Point Software Technologies, Inc.
800 Bridge Parkway
Redwood City, CA 94065
US

Email:
United States

EMail: bob.hinden@gmail.com