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rfc:rfc3307

Network Working Group B. Haberman Request for Comments: 3307 Consultant Category: Standards Track August 2002

        Allocation Guidelines for IPv6 Multicast Addresses

Status of this Memo

 This document specifies an Internet standards track protocol for the
 Internet community, and requests discussion and suggestions for
 improvements.  Please refer to the current edition of the "Internet
 Official Protocol Standards" (STD 1) for the standardization state
 and status of this protocol.  Distribution of this memo is unlimited.

Copyright Notice

 Copyright (C) The Internet Society (2002).  All Rights Reserved.

Abstract

 This document specifies guidelines that must be implemented by any
 entity responsible for allocating IPv6 multicast addresses.  This
 includes, but is not limited to, any documents or entities wishing to
 assign permanent IPv6 multicast addresses, allocate dynamic IPv6
 multicast addresses, and define permanent IPv6 multicast group
 identifiers.  The purpose of these guidelines is to reduce the
 probability of IPv6 multicast address collision, not only at the IPv6
 layer, but also at the link-layer of media that encode portions of
 the IP layer address into the MAC layer address.

Haberman Standards Track [Page 1] RFC 3307 IPv6 Multicast Addresses Guidelines August 2002

Table of Contents

 1. Terminology.....................................................2
 2. Introduction....................................................2
 3. Applicability...................................................3
 4. Group ID Selection Guidelines...................................3
 4.1  Permanent IPv6 Multicast Addresses............................4
 4.2  Permanent IPv6 Multicast Group Identifiers....................4
 4.3  Dynamic IPv6 Multicast Addresses..............................4
 4.3.1 Server Allocation............................................5
 4.3.2 Host Allocation..............................................5
 5. IANA Considerations.............................................5
 6. Security Considerations.........................................6
 7. Acknowledgements................................................6
 8. References......................................................6
 Author's Address...................................................7
 Full Copyright Statement...........................................8

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].
 The term "group ID", throughout this document, conforms to the
 definition contained in [UNIMCAST], that is, the low-order 32 bits of
 the IPv6 multicast address.

2. Introduction

 This document specifies guidelines that MUST be implemented by any
 entity responsible for allocating IPv6 multicast addresses.  This
 includes, but is not limited to, any documents or entities wishing to
 assign permanent IPv6 multicast addresses, allocate dynamic IPv6
 multicast addresses, and define permanent IPv6 multicast group
 identifiers.  The purpose of these guidelines is to reduce the
 probability of IPv6 multicast address collision, not only at the IPv6
 layer, but also at the link-layer of media that encode portions of
 the IP layer address into the link-layer address.
 With the current IPv6 address architecture [ADDRARCH] and the
 extension to the multicast address architecture specified in
 [UNIMCAST], a set of guidelines is needed for entities assigning any
 flavor of IPv6 multicast addresses.
 The current approach of several physical media [RFC 2464][RFC 2467]
 is to map a portion of the IPv6 multicast address into a link-layer
 destination address.  This is accomplished by taking the low order 32

Haberman Standards Track [Page 2] RFC 3307 IPv6 Multicast Addresses Guidelines August 2002

 bits (henceforth called the group ID) of the IPv6 multicast address
 and including them in the link-layer destination address.  Group IDs,
 less than or equal to, 32 bits long will generate unique link-layer
 addresses within a given multicast scope.
 These guidelines specify how the group ID of the IPv6 multicast
 address are chosen and assigned.  The guidelines specify several
 mechanisms that can be used to determine the group ID of the
 multicast address, based on the type of allocation being done.

3. Applicability

 These guidelines are designed to be used in any environment in which
 IPv6 multicast addresses are delegated, assigned, or selected.  These
 guidelines are not limited to use by MADCAP [RFC 2730] servers.  The
 following is a non-exhaustive list of applications of these
 guidelines:
  1. Source-specific multicast application servers can generate an

SSM group address by generating a 96-bit multicast prefix, as

       defined in [UNIMCAST] (i.e. FF3x::/96) and concatenating that
       with a group ID, as defined in this document.
  1. A MADCAP server allocates IPv6 multicast addresses conforming

to section 2.7 of [ADDRARCH], creating the group ID using the

       rules defined in this document.
  1. Nodes supplying multicast services in a zeroconf environment

generate multicast addresses without the need of centralized

       control.
  1. IANA can assign permanent multicast addresses to fulfill

requests via the protocol standardization process.

4. Group ID Selection Guidelines

 The Group ID selection process allows for three types of multicast
 address assignments.  These are permanent IPv6 multicast addresses,
 dynamic IPv6 multicast addresses, and permanent IPv6 multicast group
 IDs.  The following guidelines assume that the prefix of the
 multicast address has been initialized according to [ADDRARCH] or
 [UNIMCAST].

Haberman Standards Track [Page 3] RFC 3307 IPv6 Multicast Addresses Guidelines August 2002

4.1 Permanent IPv6 Multicast Addresses

 Permanent multicast addresses, like those defined in [RFC 2375], are
 allocated by IANA.  These addresses will be assigned with group ID's,
 in the range of 0x00000001 to 0x3FFFFFFF, on an Expert Review basis.
 Multicast addresses assigned by IANA MUST have the T bit set to 0 and
 the P bit set to 0.

4.2 Permanent IPv6 Multicast Group Identifiers

 Permanent group IDs allow for a global identifier of a particular
 service (e.g. Network Time Protocol (NTP) being assigned the group ID
 0x40404040).  The use of permanent group IDs differs from permanent
 multicast addresses in that a permanent group ID offers a global
 identifier for a service being offered by numerous servers.
 As an example, consider the NTP example group ID of 0x40404040.  An
 NTP client would be able to access multiple servers and multiple
 scopes.  That is, the NTP client will know that the group ID
 0x40404040 identifies an NTP multicast stream regardless of the upper
 96 bits of the multicast address.
 Permanent group IDs are allocated on an Expert Review basis, in the
 range 0x40000000 to 0x7FFFFFFF.  These permanent group IDs are meant
 to be used in IPv6 multicast addresses, defined in [UNIMCAST].

4.3 Dynamic IPv6 Multicast Addresses

 Dynamic IPv6 multicast addresses can be allocated by an allocation
 server or by an end-host.  Regardless of the allocation mechanism,
 all dynamically allocated IPv6 multicast addresses MUST have the T
 bit set to 1.  This will distinguish the dynamically allocated
 addresses from the permanently assigned multicast addresses, defined
 in [RFC 2375], at the link-layer on any media that maps the lower
 portion of the IPv6 multicast address into a link-layer address.  It
 should be noted that the high-order bit of the Group ID will be the
 same value as the T flag.
 As an example, the permanent IPv6 multicast address FF02::9 maps to
 an Ethernet group address of 33-33-00-00-00-09.  A dynamically
 allocated IPv6 multicast address of FF32::8000:9 would map to the
 Ethernet group address 33-33-80-00-00-09.

Haberman Standards Track [Page 4] RFC 3307 IPv6 Multicast Addresses Guidelines August 2002

4.3.1 Server Allocation

 The allocation of IPv6 multicast addresses, by a server, is defined
 in [RFC 2730].  Address management is the responsibility of the
 allocation protocol and outside the scope of this document.
 Allocation servers MUST use the group ID range 0x80000000 to
 0xFFFFFFFF.

4.3.2 Host Allocation

 Host-based allocation allows hosts to self-select IPv6 multicast
 addresses.  One example of host-based allocation is the Zeroconf
 Multicast Address Allocation Protocol [ZMAAPDOC].  Issues with
 collision detection, claim notification, etc. are outside the scope
 of this document and the responsibility of the protocol being used,
 such as [ZMAAPDOC].
 The group ID portion of the address is created using either a
 pseudo-random 32-bit number or a 32-bit number created using the
 guidelines in [RFC 1750].  The generated group ID MUST fall in the
 range 0x80000000 to 0xFFFFFFFF.  This can be accomplished by setting
 the high-order bit of the generated number to 1.

5. IANA Considerations

 This document requests the creation of a new registry maintained by
 IANA.  This new registry will maintain permanent group ID values. The
 premise of this new registry is to allow for permanent group IDs to
 be used across multiple domains utilizing the multicast address
 architecture defined in [UNIMCAST].  The permanent group IDs will
 fall in the range 0x40000000 to 0x7FFFFFFF.
 In addition, this document also defines rules for the allocation of
 permanent IPv6 multicast addresses by IANA.  These rules specify
 different ranges for multicast addresses that are IPv6-only and for
 IPv6 multicast addresses that have corresponding IPv4 multicast
 addresses.
 Following the policies outlined in [RFC 2434]:
  1. Permanent IPv6 multicast addresses with corresponding IPv4

multicast addresses, like those defined in [RFC 2375], are

       allocated with group ID's in the range of 1 to 0x3FFFFFFF on an
       Expert Review basis, see Section 4.1.

Haberman Standards Track [Page 5] RFC 3307 IPv6 Multicast Addresses Guidelines August 2002

  1. Permanent IPv6-only multicast addresses are allocated with

group ID's in the range 0x100 to 0x3FFFFFFF on an Expert Review

       basis.
    -  Permanent group ID's are allocated on an Expert Review basis in
       the range 0x40000000 to 0x7FFFFFFF, see Section 4.2.
    -  The range 0x80000000 to 0xFFFFFFFF is reserved for use by
       dynamic multicast address allocation mechanisms, see Section
       4.3.
 All approved requests for a permanent IPv6 multicast address will
 result in the assignment of a unique group ID which shall be reserved
 in all valid IPv6 multicast scopes.

6. Security Considerations

 The allocation mechanisms described in this document do not alter the
 security properties of either the Any Source or Source Specific
 multicast service models of IPv4 and IPv6.
 The potential to allocate large blocks of addresses can lead to
 Denial-of-Service attacks.  A more in-depth discussion of the
 security issues surrounding dynamic allocation of multicast addresses
 can be found in [RFC 2908].

7. Acknowledgements

 The author would like to thank Dave Thaler, Steve Deering, Allison
 Mankin, Thomas Narten, and Erik Nordmark for their thorough review of
 this document.

8. References

 [RFC 2026] Bradner, S., "The Internet Standards Process -- Revision
            3", BCP 9, RFC 2026, October 1996.
 [UNIMCAST] Haberman, B. and D. Thaler, "Unicast Prefix-based IPv6
            Multicast Addresses", RFC 3306, June 2002.
 [ADDRARCH] Hinden, R. and S. Deering, "IP Version 6 Addressing
            Architecture", RFC 2373, July 1998.
 [RFC 2119] Bradner, S., "Key words for use in RFCs to Indicate
            Requirement Levels", BCP 14, RFC 2119, March 1999.
 [RFC 2730] Hanna, S., Patel, B. and M. Shah, "Multicast Address
            Dynamic Client Allocation Protocol (MADCAP)", RFC 2730,
            December 1999.

Haberman Standards Track [Page 6] RFC 3307 IPv6 Multicast Addresses Guidelines August 2002

 [RFC 2464] Crawford, M., "Transmission of IPv6 Packets over Ethernet
            Networks", RFC 2464, December 1998.
 [RFC 2467] Crawford, M., "Transmission of IPv6 over FDDI Networks",
            RFC 2467, December 1998.
 [RFC 1750] Eastlake, D., Crocker, S. and J. Schiller, "Randomness
            Recommendations for Security", RFC 1750, December 1994.
 [RFC 2375] Hinden, R. and S. Deering, "IPv6 Multicast Address
            Assignments", RFC 2375, July 1998.
 [RFC 2908] Thaler, D., Handley, M. and D. Estrin, "The Internet
            Multicast Address Allocation Architecture", RFC 2908,
            September 2000.
 [ZMAAPDOC] Catrina, et al, "Zeroconf Multicast Address Allocation
            Protocol (ZMAAP)", Work In Progress.

Author's Address

 Brian Haberman
 Consultant
 Phone: 1-919-949-4828
 EMail: bkhabs@nc.rr.com

Haberman Standards Track [Page 7] RFC 3307 IPv6 Multicast Addresses Guidelines August 2002

Full Copyright Statement

 Copyright (C) The Internet Society (2002).  All Rights Reserved.
 This document and translations of it may be copied and furnished to
 others, and derivative works that comment on or otherwise explain it
 or assist in its implementation may be prepared, copied, published
 and distributed, in whole or in part, without restriction of any
 kind, provided that the above copyright notice and this paragraph are
 included on all such copies and derivative works.  However, this
 document itself may not be modified in any way, such as by removing
 the copyright notice or references to the Internet Society or other
 Internet organizations, except as needed for the purpose of
 developing Internet standards in which case the procedures for
 copyrights defined in the Internet Standards process must be
 followed, or as required to translate it into languages other than
 English.
 The limited permissions granted above are perpetual and will not be
 revoked by the Internet Society or its successors or assigns.
 This document and the information contained herein is provided on an
 "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
 TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
 BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
 HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
 MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

Acknowledgement

 Funding for the RFC Editor function is currently provided by the
 Internet Society.

Haberman Standards Track [Page 8]

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