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:
- 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 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.
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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]:
- 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
- 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.
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Haberman Standards Track [Page 8]
