SIP WG V. Gurbani, Ed.
Internet-Draft Bell Laboratories, Alcatel-Lucent
Updates: 3261 (if approved) B. Carpenter, Ed.
Intended status: Standards Track Univ. of Auckland
Expires: August 1, 2010 B. Tate, Ed.
BroadSoft
January 28, 2010
Essential correction for IPv6 ABNF and URI comparison in RFC3261
draft-ietf-sip-ipv6-abnf-fix-04
Abstract
This memo corrects the Augmented Backus-Naur Form (ABNF) production
rule associated with generating IPv6 literals in RFC3261. It also
clarifies the rule for Uniform Resource Identifier (URI) comparison
when the URIs contain textual representation of IP addresses.
Status of this Memo
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document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
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Table of Contents
1. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Problem statement . . . . . . . . . . . . . . . . . . . . . . . 3
2.1. Extra colon in IPv4-mapped IPv6 address . . . . . . . . . . 3
2.2. Comparing URIs with textual representation of IP
addresses . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Resolution . . . . . . . . . . . . . . . . . . . . . . . . . . 4
3.1. Resolution for extra colon in IPv4-mapped IPv6 address . . 4
3.2. Clarification for comparison of URIs with textual
representation of IP addresses . . . . . . . . . . . . . . 5
4. Security Considerations . . . . . . . . . . . . . . . . . . . . 6
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 6
6. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . 6
7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 7
7.1. Normative References . . . . . . . . . . . . . . . . . . . 7
7.2. Informative References . . . . . . . . . . . . . . . . . . 7
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 7
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1. Terminology
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 RFC 2119 [2].
2. Problem statement
2.1. Extra colon in IPv4-mapped IPv6 address
The ABNF [4] for generating IPv6 literals in RFC3261 [1] is
incorrect. When generating IPv4-mapped IPv6 addresses, the
production rule may actually generate the following construct:
[2001:db8:::192.0.2.1] - Note the extra colon before the IPv4
address.
The correct construct, of course, would only include two colons
before the IPv4 address.
Historically, the ABNF pertaining to IPv6 references in RFC3261
was derived from Appendix B of RFC 2373 [6], which was flawed to
begin with (see also RFC2373 errata at
http://www.rfc-editor.org/cgi-bin/errataSearch.pl/doc/html/rfc2373.)
RFC2373 has been subsequently obsoleted by RFC 4291 [5].
The ABNF for IPv6 reference is reproduced from RFC3261 below:
IPv6reference = "[" IPv6address "]"
IPv6address = hexpart [ ":" IPv4address ]
IPv4address = 1*3DIGIT "." 1*3DIGIT "." 1*3DIGIT "." 1*3DIGIT
hexpart = hexseq / hexseq "::" [ hexseq ] / "::" [ hexseq ]
hexseq = hex4 *( ":" hex4)
hex4 = 1*4HEXDIG
Note that the ambiguity occurs in the <IPv6address> production rule
where the <IPv4address> non-terminal is prefixed by the ":" token.
Because the <hexpart> production rule is defined such that two of its
alternatives already include the "::" token, this may yield to the
faulty construction of an IPv6-mapped IPv4 address with an extra
colon when expanding those alternatives.
2.2. Comparing URIs with textual representation of IP addresses
In SIP, URIs are compared for a variety of reasons. Registrars
compare URIs when they receive a binding update request, for
instance. Section 19.1.4 of RFC3261 [1] provides the rules for
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comparing URIs. Among other rules, it states that:
For two URIs to be equal, the user, password, host, and port
components must match.
Does the above rule then imply that the following URIs are equal:
sip:bob@[::ffff:192.0.2.128] = sip:bob@[::ffff:c000:280]?
sip:bob@[2001:db8::9:1] = sip:bob@[2001:db8::9:01]?
sip:bob@[0:0:0:0:0:FFFF:129.144.52.38] = sip:bob@
[::FFFF:129.144.52.38]?
In all of the above examples, the textual representation of the IPv6
address is different, but these addresses are binary equivalent
(implementers are also urged to consult [7] for recommendations on
IPv6 address text representations.) Section 19.1.4 of RFC3261 does
not provide any rule for URIs containing different textual
representations of IPv6 addresses that all correspond to the same
binary equivalent.
Note that the same ambiguity occurs for IPv4 addresses, i.e., is
192.0.2.128 = 192.00.02.128? However, IPv6, with its compressed
notation and the need to represent hybrid addresses (like IPv4-
mapped IPv6 addresses) makes the representation issue more acute.
The resolution discussed in Section 3.2 applies to textual
representations of both IPv6 and IPv4 addresses.
3. Resolution
3.1. Resolution for extra colon in IPv4-mapped IPv6 address
The resolution to this ambiguity is simply to use the correct ABNF
for the <IPv6address> production rule from Appendix A of RFC3986 [3].
For the sake of completeness, it is reproduced below:
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IPv6address = 6( h16 ":" ) ls32
/ "::" 5( h16 ":" ) ls32
/ [ h16 ] "::" 4( h16 ":" ) ls32
/ [ *1( h16 ":" ) h16 ] "::" 3( h16 ":" ) ls32
/ [ *2( h16 ":" ) h16 ] "::" 2( h16 ":" ) ls32
/ [ *3( h16 ":" ) h16 ] "::" h16 ":" ls32
/ [ *4( h16 ":" ) h16 ] "::" ls32
/ [ *5( h16 ":" ) h16 ] "::" h16
/ [ *6( h16 ":" ) h16 ] "::"
h16 = 1*4HEXDIG
ls32 = ( h16 ":" h16 ) / IPv4address
IPv4address = dec-octet "." dec-octet "." dec-octet "." dec-octet
dec-octet = DIGIT ; 0-9
/ %x31-39 DIGIT ; 10-99
/ "1" 2DIGIT ; 100-199
/ "2" %x30-34 DIGIT ; 200-249
/ "25" %x30-35 ; 250-255
Accordingly, this memo updates RFC3261 as follows: the <IPv6address>
and <IPv4address> production rules MUST be deleted from RFC3261 and
MUST be replaced with the production rules of the same name in
RFC3986 (and reproduced above.) These changes, when made to RFC3261,
will make <hexpart>, <hexseq>, and <hex4> production rules obsolete.
Thus this memo also mandates that the <hexpart>, <hexseq>, and <hex4>
production rules MUST be deleted from the ABNF of RFC3261.
3.2. Clarification for comparison of URIs with textual representation
of IP addresses
The resolution to this ambiguity is a simple clarification
acknowledging that the textual representation of an IP addresses
varies, but it is the binary equivalence of the IP address that must
be taken into consideration when comparing two URIs that contain
varying textual representations of an IP address.
Accordingly, the existing rule from the bulleted list in Section
19.1.4 of RFC3216 MUST be modified as follows:
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OLD:
o For two URIs to be equal, the user, password, host, and port
components must match.
NEW:
o For two URIs to be equal, the user, password, host, and port
components must match. If the host component contains a textual
representation of IP addresses, then the representation of those
IP addresses may vary. If so, the host components are considered
to match if the different textual representations yield the same
binary IP address.
In addition, the text in the following paragraph MUST be added to the
existing list of examples in Section 19.1.4 of RFC3261 in order to
demonstrate the intent of the modified rule:
The following URIs are equivalent because the underlying binary
representation of the IP addresses are the same although their
textual representations vary:
sip:bob@[::ffff:192.0.2.128]
sip:bob@[::ffff:c000:280]
sip:bob@[2001:db8::9:1]
sip:bob@[2001:db8::9:01]
sip:bob@[0:0:0:0:0:FFFF:129.144.52.38]
sip:bob@[::FFFF:129.144.52.38]
4. Security Considerations
This document does not introduce any new security considerations.
5. IANA Considerations
This document does not include any IANA considerations.
6. Acknowledgments
The ABNF for IPv6 was developed by Roy T. Fielding and Andrew Main
and published in RFC3986.
Jeroen van Bemmel, Peter Blatherwick, Gonzalo Camarillo, Paul
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Kyzivat, Jonathan Rosenberg, Michael Thomas, and Dale Worley provided
invaluable discussion points on the SIP WG mailing list on the URI
equivalency problem. Alfred Hoenes urged the use of angle brackets
(as specified in Section 2.1 of [4]) to denote productions.
7. References
7.1. Normative References
[1] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, A.,
Peterson, J., Sparks, R., Handley, M., and E. Schooler, "SIP:
Session Initiation Protocol", RFC 3261, June 2002.
[2] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
[3] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
Resource Identifier (URI): Generic Syntax", STD 66, RFC 3986,
January 2005.
[4] Crocker, D. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", STD 68, RFC 5234, January 2008.
7.2. Informative References
[5] Hinden, R. and S. Deering, "IP Version 6 Addressing
Architecture", RFC 4291, February 2006.
[6] Hinden, R. and S. Deering, "IP Version 6 Addressing
Architecture", RFC 2373, July 1998.
[7] Kawamura, S. and M. Kawashima, "A Recommendation for IPv6
Address Text Representation",
draft-ietf-6man-text-addr-representation-04 (work in progress),
January 2010.
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Authors' Addresses
Vijay K. Gurbani (editor)
Bell Laboratories, Alcatel-Lucent
1960 Lucent Lane
Room 9C-533
Naperville, IL 60563
USA
Phone: +1 630 224-0216
Email: vkg@bell-labs.com
Brian E. Carpenter (editor)
Department of Computer Science
University of Auckland
PB 92019
Auckland, 1142
New Zealand
Email: brian.e.carpenter@gmail.com
Brett Tate (editor)
BroadSoft
Email: brett@broadsoft.com
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