IPv6 Working Group J-S. Park
INTERNET DRAFT ETRI
Expires: April 2005 M-K. Shin
ETRI/NIST
H-J. Kim
ETRI
October 2004
Link Scoped IPv6 Multicast Addresses
<draft-ietf-ipv6-link-scoped-mcast-06.txt>
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Abstract
This document specifies an extension to the multicast addressing
architecture of the IPv6 protocol. The extension allows for the use
of Interface Identifiers (IIDs) to allocate multicast addresses.
When a link-local unicast address is configured at each interface
of a node, an IID is uniquely determined. After then, each node
can generate their unique multicast addresses automatically without
conflicts. Basically, it is preferred to use this method for the
link-local scope rather than unicast-prefix-based IPv6 multicast
addresses [RFC 3306].
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Table of Contents:
1. Introduction................................................2
2. Applicability...............................................2
3. Link Scoped Multicast Address Format........................3
4. Example ....................................................4
5. Considerations..............................................4
6. Security Considerations.....................................4
7. References..................................................4
8. Acknowledgments.............................................5
Author's Addresses.............................................5
1. Introduction
This specification defines an extension to the multicast portion of
the IPv6 addressing architecture [RFC 3513]. The current
architecture does not contain any built-in support for dynamic
address allocation. The extension allows for use of IIDs to
allocate multicast addresses. When a link-local unicast address is
configured at each interface of a node, an IID is uniquely
determined. After then, each node can generate their unique
multicast addresses automatically without conflicts. That is,
these addresses could safely be configured at any time after DAD
(Duplicate Address Detection) is completed.
Basically, it is preferred to use this method for the link-local
scope rather than unicast-prefix-based IPv6 multicast addresses
[RFC 3306]. This document restricts the usage of defined fields
such as scop, plen and network prefix fields of [RFC 3306].
Therefore, this document specifies encoded information for link-
local scope in multicast addresses.
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].
2. Applicability
The allocation technique in this document is designed to be used in
any environment in which link-local scope IPv6 multicast addresses
are assigned or selected. Especially, this method goes well with
nodes supplying multicast services in a zeroconf/serverless
environment. For example, multicast addresses less than or equal
to link-local scope are themselves generated by nodes supplying
multicast services without conflicts. Also, nodes which are
supplied multicast services, easily consist of multicast addresses
of multicast servers using NDP (address resolution) and well-known
group IDs.
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Consequently, this technique MUST only be used for link scoped
multicast addresses. If you want to use multicast addresses
greater than link-local scope, you need to use other methods as
described in [RFC 3306].
3. Link Scoped Multicast Address Format
[RFC 3306] defines the following format of unicast-prefix-based
IPv6 multicast addresses:
| 8 | 4 | 4 | 8 | 8 | 64 | 32 |
+--------+----+----+--------+--------+----------------+----------+
|11111111|flgs|scop|reserved| plen | network prefix | group ID |
+--------+----+----+--------+--------+----------------+----------+
Figure 1: Unicast-Prefix-based IPv6 multicast address format
This document specifies a new format that incorporates IID
information in the multicast addresses. The idea of delegating
multicast addresses can be applicable to link-local scope.
Figure 2 illustrates the new format for link scoped multicast
addresses.
| 8 | 4 | 4 | 8 | 8 | 64 | 32 |
+--------+----+----+--------+--------+----------------+----------+
|11111111|flgs|scop|reserved| LSM | IID | group ID |
+--------+----+----+--------+--------+----------------+----------+
Figure 2: Link scoped multicast IPv6 address format
flgs MUST be "0011". (The first two bits have been yet undefined,
sent as zero and ignored on receipt) flgs MUST use the same flag
defined in section 4 of [RFC 3306].
scop MUST be <= 2. It is preferred to use this method for the
link-local scope rather than unicast-prefix-based IPv6 multicast
addresses [RFC 3306].
The reserved field MUST be zero.
LSM (Link Scoped Multicast) field MUST be "1111 1111" which maps to
the plen field in [RFC 3306], whereas the plen field in [RFC 3306]
MUST NOT be greater than 64.
That is, flgs, scop, and LSM fields are used to identify whether an
address is a multicast address as specified in this document.
The IID field is used to distinguish each node from others. And
this value is obtained from the IEEE EUI-64 based interface
identifier of the link-local unicast IPv6 address. Given the use
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of this method for link-local scope, the IID embedded in the
multicast address MUST only come from the IID of the link-local
unicast address on the interface after DAD has completed. That is,
the creation of the multicast address MUST only occur after DAD has
completed as part of the auto-configuration process.
Group ID is generated to indicate multicast application and is used
to guarantee its uniqueness only in the host. It may also be set
on the basis of the guidelines outlined in [RFC 3307].
The lifetime of link scoped multicast addresses has no dependency
on the Valid Lifetime field in the Prefix Information option,
corresponding to the unicast address being used, contained in the
Router Advertisement message [RFC 2461].
4. Example
This is an example of link scoped IPv6 multicast addresses. For
example in an ethernet environment, if the link-local unicast
address is FE80::A12:34FF:FE56:7890, the link scoped multicast
prefix of the node is FF32:00FF:A12:34FF:FE56:7890::/96.
5. Considerations
Since multicast addresses are created from the unique IID, their
useful lifetime is linked to the period during which the IID is
known to be unique. Thus, it is possible to conflict between IIDs,
due to a new node joining the network that uses the same IID. The
document does not consider this case at this phase. It is another
challenging issue and out of scope of this document.
The link scoped multicast address format supports source-specific
multicast addresses by the same method, as defined by [RFC 3306].
6. Security Considerations
[RFC 3041] describes the privacy extension to IPv6 stateless
address autoconfiguration for an IID. The secure IID, generated by
[RFC 3041], can be used for consisting of a link scoped multicast
address since the uniqueness is verified by the DAD procedure as
part of the secure auto-configuration process.
7. Acknowledgements
We would like to thank Dave Thaler and Brian Haberman for his
comments related to the consistency between the unicast prefix-
based multicast draft and this one. Special thanks are due to Erik
Nordmark and Pekka Savola for valuable comments.
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8. References
Normative
[RFC 2119] S. Bradner, "Key words for use in RFCs to indicate
Requirement Levels", RFC 2119, March 1997.
[RFC 2461] T. Narten, E. Nordmark and W. Simpson, "Neighbor
Discovery for IP Version 6 (IPv6)", RFC 2461,
December 1998.
[RFC 3041] T. Narten and R. Draves, "Privacy Extensions for
Stateless Address Autoconfiguration in IPv6,"
RFC 3041, April 2001.
[RFC 3306] B. Haberman and D. Thaler, "Unicast-Prefix-based IPv6
Multicast Addresses," RFC 3306, August 2002.
[RFC 3307] B. Haberman, "Allocation Guidelines for IPv6 Multicast
Addresses," RFC 3307, August 2002.
[RFC 3513] R. Hinden and S. Deering, "IP Version 6 Addressing
Architecture", RFC 3513, April 2003.
Informative
[SSM ARCH] H. Holbrook and B. Cain, "Source-Specific Multicast
for IP", Work In Progress, September 2004.
Authors' Addresses
Jung-Soo Park
ETRI PEC
161 Gajeong-Dong, Yuseong-Gu, Daejeon 305-350, Korea
Phone: +82 42 860 6514
Email: jspark@pec.etri.re.kr
Myung-Ki Shin
ETRI/NIST
820 West Diamond Avenue
Gaithersburg, MD 20899, USA
Tel : +1 301 975-3613
Fax : +1 301 590-0932
E-mail : mshin@nist.gov
Hyoung-Jun Kim
ETRI PEC
161 Gajeong-Dong, Yuseong-Gu, Daejeon 305-350, Korea
Phone: +82 42 860 6576
Email: khj@etri.re.kr
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