Network Working Group J-S. Park
Request for Comments: 4489 M-K. Shin
Updates: 3306 H-J. Kim
Category: Standards Track ETRI
April 2006
A Method for Generating Link-Scoped 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 (2006).
Abstract
This document specifies an extension to the multicast addressing
architecture of the IPv6 protocol. The extension allows 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 that, each node can generate
its unique multicast addresses automatically without conflicts. The
alternative method for creating link-local multicast addresses
proposed in this document is better than known methods like unicast-
prefix-based IPv6 multicast addresses. This memo updates RFC 3306.
Table of Contents:
1. Introduction ....................................................2
2. Applicability ...................................................2
3. Link-Scoped Multicast Address Format ............................3
4. Example .........................................................3
5. Consideration of Lifetime .......................................4
6. Security Considerations .........................................4
7. Acknowledgements ................................................4
8. References ......................................................5
Park, et al. Standards Track [Page 1]RFC 4489 Link-Scoped IPv6 Multicast April 2006
1. Introduction
This document defines an extension to the multicast portion of the
IPv6 addressing architecture [RFC4291]. 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 that, each node can
generate its unique multicast addresses automatically without
conflicts. That is, these addresses could safely be configured at
any time after Duplicate Address Detection (DAD) has completed.
This method for the link-local scope is preferred over unicast-
prefix-based IPv6 multicast addresses [RFC3306], since by delegating
multicast addresses using the IID, each node can generate its
multicast addresses automatically without allocation servers. This
method works better than the unicast-prefix-based method with
applications in serverless environments such as ad-hoc and network
mobility. This document restricts the usage of defined fields such
as the scop, plen, and network prefix fields of [RFC3306].
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 [RFC2119].
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. This method goes especially 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, hosts that are supplied
multicast services from multicast servers then make multicast
addresses of multicast servers using ND (address resolution) and
well-known group IDs [RFC2461].
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
[RFC3306].
Park, et al. Standards Track [Page 2]
RFC 4489 Link-Scoped IPv6 Multicast April 2006
3. Link-Scoped Multicast Address Format
This document specifies a new format that incorporates IID in the
link-local scope multicast addresses.
Figure 1 illustrates the new format for link-scoped multicast
addresses.
| 8 | 4 | 4 | 8 | 8 | 64 | 32 |
+--------+----+----+--------+--------+----------------+----------+
|11111111|flgs|scop|reserved| plen | IID | group ID |
+--------+----+----+--------+--------+----------------+----------+
Figure 1. Link-Scoped Multicast IPv6 Address Format
The flgs, scop, and plen fields are used to identify whether an
address is a multicast address, as follows:
1. flgs MUST be "0011".
2. scop MUST be <= 2.
3. The reserved field MUST be zero.
4. The "plen" field is a special value, "1111 1111" (decimal 255).
The IID field (replacing the 64-bit prefix field from [RFC3306]) is
used to distinguish each node from others. Given the use 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 a 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 [RFC3307].
4. 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.
Park, et al. Standards Track [Page 3]RFC 4489 Link-Scoped IPv6 Multicast April 2006
5. Consideration of Lifetime
Generally, link-scoped multicast addresses have no lifetime, because
link-local unicast addresses also have no lifetime. However, this is
not true in the mobile environment. Even though multicast addresses
are created from the unique IIDs of unicast addresses, their useful
lifetime is linked to the period during which the IID is known to be
unique. Thus, conflict is possible between IIDs, due to a new node
in merged network that uses the same IID as a powered node.
In this scenario, DAD also fails to guarantee uniqueness of the
unicast address, but this document does not try to address this
issue.
6. Security Considerations
The uniqueness of multicast addresses using this method is guaranteed
by the DAD process. So, a secure DAD process is needed for stability
of this method. This document proposes the mechanism in [RFC3041]
for this purpose.
[RFC3041] describes the privacy extension to IPv6 stateless address
autoconfiguration to configure the IID of non-link-local scope
unicast addresses. [RFC3041] cannot be used for making a link-local
unicast address, and hence it cannot be used to create an IID for
link-scoped multicast address. However, as [RFC3041] does not
protect the privacy of link-local unicast addresses, it does not seem
to be required to protect the privacy of IID-based link-local
multicast addresses.
7. Acknowledgements
We would like to thank Dave Thaler and Brian Haberman for their
comments related to the consistency between the unicast prefix-based
multicast document and this one. Special thanks are due to Erik
Nordmark and Pekka Savola for valuable comments.
Park, et al. Standards Track [Page 4]
RFC 4489 Link-Scoped IPv6 Multicast April 2006
8. References
8.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2461] Narten, T., Nordmark, E., and W. Simpson, "Neighbor
Discovery for IP Version 6 (IPv6)", RFC 2461, December
1998..ti 3
[RFC3041] Narten, T. and R. Draves, "Privacy Extensions for
Stateless Address Autoconfiguration in IPv6", RFC 3041,
January 2001.
[RFC3306] Haberman, B. and D. Thaler, "Unicast-Prefix-based IPv6
Multicast Addresses", RFC 3306, August 2002.
[RFC3307] Haberman, B., "Allocation Guidelines for IPv6 Multicast
Addresses", RFC 3307, August 2002.
[RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing
Architecture", RFC 4291, February 2006.
Authors' Addresses
Jung-Soo Park
ETRI PEC
161 Gajeong-Dong, Yuseong-Gu, Daejeon 305-350, Korea
Phone: +82 42 860 6514
EMail: pjs@etri.re.kr
Myung-Ki Shin
ETRI PEC
161 Gajeong-Dong, Yuseong-Gu, Daejeon 305-350, Korea
Phone: +82 42 860 4847
EMail: myungki.shin@gmail.com
Hyoung-Jun Kim
ETRI PEC
161 Gajeong-Dong, Yuseong-Gu, Daejeon 305-350, Korea
Phone: +82 42 860 6576
EMail: khj@etri.re.kr
Park, et al. Standards Track [Page 5]RFC 4489 Link-Scoped IPv6 Multicast April 2006
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Internet Society.
Park, et al. Standards Track [Page 6]
