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Network Working Group                                        B. HabermanRequest for Comments: 3307                                    ConsultantCategory: Standards Track                                    August 2002Allocation Guidelines for IPv6 Multicast AddressesStatus 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 2002Table of Contents1. Terminology.....................................................22. Introduction....................................................23. Applicability...................................................34. Group ID Selection Guidelines...................................34.1  Permanent IPv6 Multicast Addresses............................44.2  Permanent IPv6 Multicast Group Identifiers....................44.3  Dynamic IPv6 Multicast Addresses..............................44.3.1 Server Allocation............................................54.3.2 Host Allocation..............................................55. IANA Considerations.............................................56. Security Considerations.........................................67. Acknowledgements................................................68. References......................................................6   Author's Address...................................................7   Full Copyright Statement...........................................81. 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 32Haberman                    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:      -  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.      -  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.      -  Nodes supplying multicast services in a zeroconf environment         generate multicast addresses without the need of centralized         control.      -  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 20024.1  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 20024.3.1 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]:      -  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, seeSection 4.1.Haberman                    Standards Track                     [Page 5]

RFC 3307          IPv6 Multicast Addresses Guidelines        August 2002      -  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, seeSection 4.2.      -  The range 0x80000000 to 0xFFFFFFFF is reserved for use by         dynamic multicast address allocation mechanisms, seeSection4.3.   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.comHaberman                    Standards Track                     [Page 7]

RFC 3307          IPv6 Multicast Addresses Guidelines        August 2002Full 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]