6man Working Group M. Boucadair
Internet-Draft France Telecom
Updates: 3306,3956,4291 (if approved) S. Venaas
Intended status: Standards Track Cisco
Expires: August 17, 2014 February 13, 2014

Updates to the IPv6 Multicast Addressing Architecture
draft-ietf-6man-multicast-addr-arch-update-03

Abstract

This document updates the IPv6 multicast addressing architecture by defining the 17-20 reserved bits as generic flag bits. The document provides also some clarifications related to the use of these flag bits.

This document updates RFC 3956, RFC 3306 and RFC 4291.

Requirements Language

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 [RFC2119].

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 working documents as Internet-Drafts. The list of current Internet-Drafts is at http://datatracker.ietf.org/drafts/current/.

Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress."

This Internet-Draft will expire on August 17, 2014.

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Table of Contents

1. Introduction

This document updates the IPv6 multicast addressing architecture [RFC4291] by defining the 17-20 reserved bits as generic flag bits (Section 2). The document provides also some clarifications related to the use of these flag bits (Section 3).

This document updates [RFC3956], [RFC3306], and [RFC4291]. These updates are logical consequences of the recommendation on the flag bits (Section 3).

Textual representation of IPv6 addresses included in the RFC updates follows the recommendation in [RFC5952].

2. Addressing Architecture Update

Bits 17-20 of a multicast address are defined in [RFC3956] and [RFC3306] as reserved bits. This document defines these bits as generic flag bits so that they apply to any multicast address. Figure 1 and Figure 2 show the updated structure of the addressing architecture. The first diagram shows the update of the base IPv6 addressing architecture, and the second shows the update of so-called Embedded-RP.

OLD: 
|   8    |  4 |  4 |                  112 bits                    |
+--------+----+----+----------------------------------------------+
|11111111|flgs|scop|                  group ID                    |
+--------+----+----+----------------------------------------------+

NEW:
|   8    |  4 |  4 |  4 |             108 bits                    |
+--------+----+----+----------------------------------------------+
|11111111|ff1 |scop|ff2 |             group ID                    |
+--------+----+----+----+-----------------------------------------+

     * ff1 refers to "flag field 1"
     * ff2 refers to "flag field 2"
     * flag bits denote both ff1 and ff2.

Figure 1: Updated IPv6 Multicast Addressing Architecture

OLD (RFC 3956):
|   8    |  4 |  4 |  4 |  4 |   8    |       64       |    32    |
+--------+----+----+----+----+--------+----------------+----------+
|11111111|flgs|scop|rsvd|RIID|  plen  | network prefix | group ID |
+--------+----+----+----+----+--------+----------------+----------+

NEW:
|   8    |  4 |  4 |  4 |  4 |   8    |       64       |    32    |
+--------+----+----+----+----+--------+----------------+----------+
|11111111|ff1 |scop|ff2 |RIID|  plen  | network prefix | group ID |
+--------+----+----+----+----+--------+----------------+----------+

Figure 2: Embedded-RP with Updated IPv6 Multicast Address Arch.

Further specification documents may define a meaning for these flag bits. Defining the bits 17-20 as flags for all IPv6 multicast addresses allows addresses to be treated in a more uniform and generic way, and allows for these bits to be defined in the future for different purposes, irrespective of the specific type of multicast address.

3. Flag Bits: A Recommendation

Some implementations and specification documents do not treat the flag bits as separate bits but tend to use their combined value as a 4-bit integer. This practice is a hurdle for assigning a meaning to the remaining flag bits. Below are listed some examples for illustration purposes:

  • the reading of [RFC3306] may lead to conclude that ff3x::/32 is the only allowed SSM IPv6 prefix block.
  • [RFC3956] states only ff70::/12 applies to Embedded-RP. Particularly, implementations should not treat the fff0::/12 range as Embedded-RP.

To avoid such confusion and to unambiguously associate a meaning with the remaining flags, the following requirement is made

  • Implementations MUST treat flag bits as separate bits.

4. RFC Updates

4.1. RFC 3306

This document changes Section 4 of [RFC3306] as follows:

OLD:

      |   8    |  4 |  4 |   8    |    8   |       64       |    32    |
      +--------+----+----+--------+--------+----------------+----------+
      |11111111|flgs|scop|reserved|  plen  | network prefix | group ID |
      +--------+----+----+--------+--------+----------------+----------+

                                   +-+-+-+-+
   flgs is a set of 4 flags:       |0|0|P|T|
                                   +-+-+-+-+

         o  P = 0 indicates a multicast address that is not assigned
            based on the network prefix.  This indicates a multicast
            address as defined in [ADDRARCH].

         o  P = 1 indicates a multicast address that is assigned based
            on the network prefix.

         o  If P = 1, T MUST be set to 1, otherwise the setting of the T
            bit is defined in Section 2.7 of [ADDRARCH].

   The reserved field MUST be zero.

NEW:

      |   8    |  4 |  4 |  4 |  4 |    8   |       64       |    32    |
      +--------+----+----+----+----+--------+----------------+----------+
      |11111111|ff1 |scop|ff2 |rsvd|  plen  | network prefix | group ID |
      +--------+----+----+----+----+--------+----------------+----------+

                                                  +-+-+-+-+
   ff1 (flag field 1) is a set of 4 flags:        |X|Y|P|T|  
                                                  +-+-+-+-+

   X and Y may each be set to 0 or 1.

         o  P = 0 indicates a multicast address that is not assigned
            based on the network prefix.  This indicates a multicast
            address as defined in [RFC4291].

         o  P = 1 indicates a multicast address that is assigned based
            on the network prefix.

         o  If P = 1, T MUST be set to 1, otherwise the setting of the T
            bit is defined in Section 2.7 of [RFC4291].

                                                  +-+-+-+-+
   ff2 (flag field 2) is a set of 4 flags:        |r|r|r|r|  
                                                  +-+-+-+-+

   where "rrrr" are for future assignment as additional flag bits.

   Flag bits denote both ff1 and ff2.

This document changes Section 6 of [RFC3306] as follows:

OLD:

  • These settings create an SSM range of FF3x::/32 (where 'x' is any valid scope value). The source address field in the IPv6 header identifies the owner of the multicast address.

NEW:

  • If the flag bits in ff1 are set to 0011, these settings create an SSM range of ff3x::/32 (where 'x' is any valid scope value). The source address field in the IPv6 header identifies the owner of the multicast address. ff3x::/32 is not the only allowed SSM prefix range. For example if the most significant flag bit in ff1 is set, then we would get the SSM range ffbx::/32.

4.2. RFC 3956

This document changes Section 2 of [RFC3956] as follows:

OLD:

   As described in [RFC3306], the multicast address format is as
   follows:

      |   8    |  4 |  4 |   8    | 8  |       64       |    32    |
      +--------+----+----+--------+----+----------------+----------+
      |11111111|flgs|scop|reserved|plen| network prefix | group ID |
      +--------+----+----+--------+----+----------------+----------+

   Where flgs are "0011".  (The first two bits are as yet undefined,
   sent as zero and ignored on receipt.)

   The multicast address format is as
   follows:

      |   8    |  4 |  4 |  4 |  4 | 8  |       64       |    32    |
      +--------+----+----+----+----+----+----------------+----------+
      |11111111|ff1 |scop|ff2 |rsvd|plen| network prefix | group ID |
      +--------+----+----+----+----+----+----------------+----------+

                                                     +-+-+-+-+
      ff1 (flag field 1) is a set of four flags:     |X|R|P|T|
                                                     +-+-+-+-+
      X may be set to 0 or 1.

                                                     +-+-+-+-+
      ff2 (flag field 2) is a set of 4 flags:        |r|r|r|r|  
                                                     +-+-+-+-+
      where "rrrr" are for future assignment as additional flag bits.

      Flag bits denote both ff1 and ff2.

This document changes Section 3 of [RFC3956] as follows:

OLD:

      |   8    |  4 |  4 |  4 |  4 | 8  |       64       |    32    |
      +--------+----+----+----+----+----+----------------+----------+
      |11111111|flgs|scop|rsvd|RIID|plen| network prefix | group ID |
      +--------+----+----+----+----+----+----------------+----------+
                                      +-+-+-+-+
      flgs is a set of four flags:    |0|R|P|T|
                                      +-+-+-+-+

   When the highest-order bit is 0, R = 1 indicates a multicast address
   that embeds the address on the RP.  Then P MUST be set to 1, and
   consequently T MUST be set to 1, as specified in [RFC3306].  In
   effect, this implies the prefix FF70::/12.  In this case, the last 4
   bits of the previously reserved field are interpreted as embedding
   the RP interface ID, as specified in this memo.

   The behavior is unspecified if P or T is not set to 1, as then the
   prefix would not be FF70::/12.  Likewise, the encoding and the
   protocol mode used when the two high-order bits in "flgs" are set to
   11 ("FFF0::/12") is intentionally unspecified until such time that
   the highest-order bit is defined.  Without further IETF
   specification, implementations SHOULD NOT treat the FFF0::/12 range
   as Embedded-RP.

NEW:

      |   8    |  4 |  4 |  4 |  4 | 8  |       64       |    32    |
      +--------+----+----+----+----+----+----------------+----------+
      |11111111|ff1 |scop|ff2 |RIID|plen| network prefix | group ID |
      +--------+----+----+----+----+----+----------------+----------+
                                      +-+-+-+-+
      ff1 is a set of four flags:     |X|R|P|T|
                                      +-+-+-+-+
      X may be set to 0 or 1.

   R = 1 indicates a multicast address that embeds the address of the RP.
   P MUST be set to 1, and consequently T MUST be set to 1, according
   to [RFC3306], as this is a special case of
   unicast-prefix based addresses. This implies that for instance prefixes
   ff70::/12 and fff0::/12 are embedded RP prefixes. 
   The behavior is unspecified if P or T is not set to 1. When the
   R-bit is set, the last 4 bits of the previously reserved field are
   interpreted as embedding the RP interface ID, as specified in this memo.

This document changes Section 4 of [RFC3956] as follows:

OLD:

  • It MUST be a multicast address with "flgs" set to 0111, that is, to be of the prefix FF70::/12,

NEW:

  • It MUST be a multicast address with R-bit set to 1.
  • It MUST have P-bit and T-bit both set to 1 when using the embedding in this document as it is a prefix-based address.

This document changes Section 7.1 of [RFC3956] as follows:

OLD:

  • To avoid loops and inconsistencies, for addresses in the range FF70::/12, the Embedded-RP mapping MUST be considered the longest possible match and higher priority than any other mechanism.

NEW:

  • To avoid loops and inconsistencies, for addresses with R-bit set to 1, the Embedded-RP mapping MUST be considered the longest possible match and higher priority than any other mechanism.

5. IANA Considerations

This document does not require any action from IANA.

6. Security Considerations

Security considerations discussed in [RFC3956], [RFC3306] and [RFC4291] MUST be taken into account.

7. Acknowledgements

Special thanks to B. Haberman for the discussions prior to the publication of this document.

Many thanks to J. Korhonen and T. Jinmei their comments.

8. Normative References

[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3956] Savola, P. and B. Haberman, "Embedding the Rendezvous Point (RP) Address in an IPv6 Multicast Address", RFC 3956, November 2004.
[RFC3306] Haberman, B. and D. Thaler, "Unicast-Prefix-based IPv6 Multicast Addresses", RFC 3306, August 2002.
[RFC5952] Kawamura, S. and M. Kawashima, "A Recommendation for IPv6 Address Text Representation", RFC 5952, August 2010.
[RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing Architecture", RFC 4291, February 2006.

Authors' Addresses

Mohamed Boucadair France Telecom Rennes, 35000 France EMail: mohamed.boucadair@orange.com
Stig Venaas Cisco USA EMail: stig@cisco.com