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Internet Engineering Task Force (IETF)                   V. Gurbani, Ed.Request for Comments: 5954             Bell Laboratories, Alcatel-LucentUpdates:3261                                          B. Carpenter, Ed.Category: Standards Track                              Univ. of AucklandISSN: 2070-1721                                             B. Tate, Ed.                                                               BroadSoft                                                             August 2010Essential Correction for IPv6 ABNF and URI Comparison inRFC 3261Abstract   This document corrects the Augmented Backus-Naur Form (ABNF)   production rule associated with generating IPv6 literals inRFC 3261.   It also clarifies the rule for Uniform Resource Identifier (URI)   comparison when the URIs contain textual representation of IP   addresses.Status of This Memo   This is an Internet Standards Track document.   This document is a product of the Internet Engineering Task Force   (IETF).  It represents the consensus of the IETF community.  It has   received public review and has been approved for publication by the   Internet Engineering Steering Group (IESG).  Further information on   Internet Standards is available inSection 2 of RFC 5741.   Information about the current status of this document, any errata,   and how to provide feedback on it may be obtained athttp://www.rfc-editor.org/info/rfc5954.Copyright Notice   Copyright (c) 2010 IETF Trust and the persons identified as the   document authors.  All rights reserved.   This document is subject toBCP 78 and the IETF Trust's Legal   Provisions Relating to IETF Documents   (http://trustee.ietf.org/license-info) in effect on the date of   publication of this document.  Please review these documents   carefully, as they describe your rights and restrictions with respect   to this document.  Code Components extracted from this document must   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.Gurbani, et al.              Standards Track                    [Page 1]

RFC 5954                      SIP IPv6 ABNF                  August 2010Table of Contents1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . .22.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . . .23.  Problem Statement . . . . . . . . . . . . . . . . . . . . . . .23.1.  Extra Colon in IPv4-Mapped IPv6 Address . . . . . . . . . .2     3.2.  Comparing URIs with Textual Representation of IP           Addresses . . . . . . . . . . . . . . . . . . . . . . . . .34.  Resolution  . . . . . . . . . . . . . . . . . . . . . . . . . .44.1.  Resolution for Extra Colon in IPv4-Mapped IPv6 Address  . .4     4.2.  Clarification for Comparison of URIs with Textual           Representation of IP Addresses  . . . . . . . . . . . . . .55.  Generating a Canonical IPv6 Textual Representation  . . . . . .56.  Security Considerations . . . . . . . . . . . . . . . . . . . .67.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . .68.  References  . . . . . . . . . . . . . . . . . . . . . . . . . .68.1.  Normative References  . . . . . . . . . . . . . . . . . . .68.2.  Informative References  . . . . . . . . . . . . . . . . . .61.  Introduction   This document corrects the Augmented Backus-Naur Form (ABNF)   production rule associated with generating IPv6 literals inRFC 3261   [1].  It also clarifies the rule for Uniform Resource Identifier   (URI) comparison when the URIs contain textual representation of IP   addresses.2.  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 inRFC 2119 [2].3.  Problem Statement3.1.  Extra Colon in IPv4-Mapped IPv6 Address   The ABNF [4] for generating IPv6 literals inRFC 3261 [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.Gurbani, et al.              Standards Track                    [Page 2]

RFC 5954                      SIP IPv6 ABNF                  August 2010      Historically, the ABNF pertaining to IPv6 references inRFC 3261      was derived fromAppendix B of RFC 2373 [7], which was flawed to      begin with (see errata forRFC 2373 [8]).RFC 2373 has been      subsequently obsoleted byRFC 4291 [6].   The ABNF for IPv6reference is reproduced fromRFC 3261 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.3.2.  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 RFC 3261 [1] provides the rules for   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 equivalents   (implementers are also urged to consultSection 5 of this document   for recommendations on IPv6 address text representations).Section19.1.4 of RFC 3261 does not provide any rule for URIs containing   different textual representations of IPv6 addresses that all   correspond to the same binary equivalent.Gurbani, et al.              Standards Track                    [Page 3]

RFC 5954                      SIP IPv6 ABNF                  August 2010      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 inSection 4.2 applies to textual      representations of both IPv6 and IPv4 addresses.4.  Resolution4.1.  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 fromAppendix A of RFC 3986   [3].  For the sake of completeness, it is reproduced below:     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 document updatesRFC 3261 as follows:  the   <IPv6address> and <IPv4address> production rules fromRFC 3261 MUST   NOT be used and instead, the production rules of the same name inRFC3986 (and reproduced above) MUST be used.  This will render   <hexpart>, <hexseq>, and <hex4> production rules inRFC 3261   obsolete; as such, these three production rules -- namely, <hexpart>,   <hexseq>, and <hex4> -- fromRFC 3261 MUST NOT be used.   The use of the <IPv4address> production rule fromRFC 3986 no longer   allows syntactically valid -- though semantically invalid -- SIP URIs   of the form "sip:bob@444.555.666.777".Gurbani, et al.              Standards Track                    [Page 4]

RFC 5954                      SIP IPv6 ABNF                  August 20104.2.  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 address   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 inSection19.1.4 of RFC 3261 MUST be modified as follows:   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 inSection 19.1.4 of RFC 3261 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]5.  Generating a Canonical IPv6 Textual Representation   Implementers SHOULD generate IPv6 text representation as defined inRFC 5952 [5].Gurbani, et al.              Standards Track                    [Page 5]

RFC 5954                      SIP IPv6 ABNF                  August 20106.  Security Considerations   This document does not introduce any new security considerations   beyond those described inRFC 3261 [1].7.  Acknowledgments   The ABNF for IPv6 was developed by Roy T. Fielding and Andrew Main   and published inRFC 3986.   Jeroen van Bemmel, Peter Blatherwick, Gonzalo Camarillo, Paul   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 inSection 2.1 of RFC 5234 [4]) to denote productions.8.  References8.1.  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.   [5]  Kawamura, S. and M. Kawashima, "A Recommendation for IPv6        Address Text Representation",RFC 5952, August 2010.8.2.  Informative References   [6]  Hinden, R. and S. Deering, "IP Version 6 Addressing        Architecture",RFC 4291, February 2006.   [7]  Hinden, R. and S. Deering, "IP Version 6 Addressing        Architecture",RFC 2373, July 1998.   [8]  "RFC Editor Errata", <http://www.rfc-editor.org/errata.php>.Gurbani, et al.              Standards Track                    [Page 6]

RFC 5954                      SIP IPv6 ABNF                  August 2010Authors' 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.comGurbani, et al.              Standards Track                    [Page 7]