6man Working Group M. Boucadair
Internet-Draft France Telecom
Updates: 3306,3956,4607,4291 (if approved) S. Venaas
Intended status: Standards Track Cisco
Expires: November 24, 2013 May 23, 2013

Updates to the IPv6 Multicast Addressing Architecture
draft-ietf-6man-multicast-addr-arch-update-01

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, RFC 4607 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 November 24, 2013.

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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 3.1) and also about IANA assigned SSM blocks (Section 3.2).

This document updates [RFC3956], [RFC3306], [RFC4607] and [RFC4291].

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|flgs|scop|flgs|             group ID                    |
+--------+----+----+----+-----------------------------------------+

Figure 1: Updated IPv6 Multicast Addressing Architecture

OLD (RFC3956):
|   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|flgs|scop|flgs|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. Clarifications

3.1. Flag Bits

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 [RFC4607] 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 recommendation is made

  • Implementations MUST treat flag bits as separate bits.

3.2. IANA Assigned SSM Block

Another issue related to SSM is the IANA assigned SSM address block. Per [RFC4607], ff3x::4000:0001 through ff3x::7fff:fff is the block for IANA assignments (http://www.iana.org/assignments/ipv6-multicast-addresses/ipv6-multicast-addresses.xml). However, IANA assignments are permanent addresses and should not have the transient bit set. Quoting from [RFC4607]:

  • "T = 1 indicates a non-permanently-assigned ("transient") multicast address.".

4. RFC Updates

4.1. RFC3306

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

                                   +-+-+-+-+
   flgs 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 [ADDRARCH].

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

         o  T is set according to the definition in Section 2.7 
            of [ADDRARCH]. Unicast-Prefix-based addresses would 
            typically not be IANA assigned, so in most cases T would 
            be set to 1.

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:

  • T flag is set according to whether the addresses are assigned by IANA.
  • If the flag bits are 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, ff2x::/32 would be IANA assigned SSM addresses.

4.2. RFC3956

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.)

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

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

                                      +-+-+-+-+
      flgs is a set of four flags:    |X|R|P|T|
                                      +-+-+-+-+

      X may be set to 0 or 1.

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|flgs|scop|flgs|RIID|plen| network prefix | group ID |
      +--------+----+----+----+----+----+----------------+----------+
                                      +-+-+-+-+
      flgs 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 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, but all multicast
   addresses with the R-bit set to 1 MUST be treated as Embedded RP
   addresses. The behavior is unspecified if P 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 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.

4.3. RFC4607

This document changes the abstract of [RFC4607] as follows:

OLD:

  • IP version 4 (IPv4) addresses in the 232/8 (232.0.0.0 to 232.255.255.255) range are designated as source-specific multicast (SSM) destination addresses and are reserved for use by source- specific applications and protocols. For IP version 6 (IPv6), the address prefix FF3x::/32 is currently reserved for source-specific multicast use but others may be reserved in the future. This document defines an extension to the Internet network service that applies to datagrams sent to SSM addresses and defines the host and router requirements to support this extension.

NEW:

  • IP version 4 (IPv4) addresses in the 232/8 (232.0.0.0 to 232.255.255.255) range are designated as source-specific multicast (SSM) destination addresses and are reserved for use by source- specific applications and protocols. For IP version 6 (IPv6), the address prefix ff3x::/32 is currently reserved for source-specific multicast use but others may be reserved in the future. This document defines an extension to the Internet network service that applies to datagrams sent to SSM addresses and defines the host and router requirements to support this extension.

This document changes Section 1 of [RFC4607] as follows:

OLD:

  • For IPv6, the address prefix FF3x::/32 is reserved for source- specific multicast use, where 'x' is any valid scope identifier, by [IPv6-UBM]. Using the terminology of [IPv6-UBM], all SSM addresses must have P=1, T=1, and plen=0. [IPv6-MALLOC] mandates that the network prefix field of an SSM address also be set to zero, hence all SSM addresses fall in the FF3x::/96 range. Future documents may allow a non-zero network prefix field if, for instance, a new IP- address-to-MAC-address mapping is defined. Thus, address allocation should occur within the FF3x::/96 range, but a system should treat all of FF3x::/32 as SSM addresses, to allow for compatibility with possible future uses of the network prefix field.

NEW:

  • For IPv6, all SSM addresses must have P=1 and plen=0 while T-bit is set according to whether the addresses are assigned by IANA [I-D.ietf-6man-multicast-addr-arch-update]. In particular, a system should treat all of ff3x::/32 and ff2x::/32 as SSM addresses, to allow for compatibility with possible future uses of the network prefix field. Other SSM prefixes can be defined in the future.

5. IANA Considerations

This document may require IANA updates. However, at this point it is not clear exactly what these updates may be.

6. Security Considerations

Security considerations discussed in [RFC3956], [RFC3306], [RFC4607] and [RFC4291] MUST be taken into account.

7. Acknowledgements

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

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.
[RFC4607] Holbrook, H. and B. Cain, "Source-Specific Multicast for IP", RFC 4607, August 2006.
[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