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Versions: 00 draft-ietf-sip-ipv6-abnf-fix

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:  May 8, 2008                                   November 5, 2007


             Essential correction for IPv6 ABNF in RFC3261
                   draft-gurbani-sip-ipv6-abnf-fix-00

Status of this Memo

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   This Internet-Draft will expire on May 8, 2008.

Copyright Notice

   Copyright (C) The IETF Trust (2007).

Abstract

   This memo corrects the Augmented Backus-Naur Form (ABNF) production
   rule associated with generating IPv6 literals in RFC3261








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Table of Contents

   1.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . 3
   2.  Problem statement . . . . . . . . . . . . . . . . . . . . . . . 3
   3.  Resolution  . . . . . . . . . . . . . . . . . . . . . . . . . . 3
   4.  Security Considerations . . . . . . . . . . . . . . . . . . . . 4
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 4
   6.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . 4
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . . . 5
     7.1.  Normative References  . . . . . . . . . . . . . . . . . . . 5
     7.2.  Informative References  . . . . . . . . . . . . . . . . . . 5
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . . . 5
   Intellectual Property and Copyright Statements  . . . . . . . . . . 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

   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?rfc=2373.)
      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 ":" 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.  Resolution

   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, following the SIP essential corrections process [7],
   this memo RECOMMENDS that the "IPv6address" and "IPv4address"
   production rules be deleted from RFC3261 and 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 RECOMMENDS that
   the "hexpart", "hexseq", and "hex4" production rules be deleted from
   the ABNF of RFC3261.


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 correct ABNF for IPv6 was developed by Andrew Main
   (draft-main-ipaddr-text-rep) in 2005 and published in RFC3986.


7.  References




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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., Ed. and P. Overell, "Augmented BNF for Syntax
        Specifications: ABNF", RFC 4234, October 2005.

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]  Drage, K., "A Process for Handling Essential Corrections to the
        Session Initiation  Protocol (SIP)",
        draft-drage-sip-essential-correction-01 (work in progress),
        March 2007.


Authors' Addresses

   Vijay K. Gurbani (editor)
   Bell Laboratories, Alcatel-Lucent
   2701 Lucent Lane
   Room 9F-546
   Lisle, IL  60532
   USA

   Phone:  +1 630 224-0216
   Email:  vkg at bell hyphen labs dot com










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   Brian E. Carpenter (editor)
   Department of Computer Science
   University of Auckland
   PB 92019
   Auckland,   1142
   New Zealand

   Email:  brian.e.carpenter@gmail.com











































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