Internet DRAFT - draft-ietf-ipngwg-uni-based-mcast
draft-ietf-ipngwg-uni-based-mcast
IPNGWG Working Group B. Haberman
Internet Draft Nortel Networks
draft-ietf-ipngwg-uni-based-mcast-03.txt D. Thaler
October 2001 Microsoft
Expires April 2002
Unicast-Prefix-based IPv6 Multicast Addresses
Status of this Memo
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026 [RFC 2026].
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as Internet-
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documents at any time. It is inappropriate to use Internet-Drafts as
reference material or to cite them other than as "work in progress."
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt.
The list of Internet-Draft Shadow Directories can be accessed at
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Abstract
This specification defines an extension to the multicast addressing
architecture of the IP Version 6 protocol. The extension presented
in this document allows for unicast-prefix-based allocation of
multicast addresses. By delegating multicast addresses at the same
time as unicast prefixes, network operators will be able to identify
their multicast addresses without needing to run an inter-domain
allocation protocol.
Table of Contents
Status of this Memo................................................1
Abstract...........................................................1
1. Introduction....................................................2
2. Motivation......................................................2
3. Terminology.....................................................2
4. Multicast Address Format........................................2
5. Address Lifetime................................................3
6. Source-Specific Multicast Addresses.............................4
7. Examples........................................................4
8. Security Considerations.........................................4
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Internet Draft Unicast Prefix-based IPv6 Multicast October 2001
9. References......................................................5
AuthorĘs Address...................................................6
Full Copyright Statement...........................................6
1. Introduction
This document specifies an extension to the multicast portion of the
IPv6 addressing architecture [ADDRARCH]. The current architecture
does not contain any built-in support for dynamic address
allocation. This proposal introduces encoded information in the
multicast address to allow for dynamic allocation of IPv6 multicast
addresses and IPv6 source-specific multicast addresses.
2. Motivation
The current IPv4 multicast address allocation architecture [RFC
2908] is based on a multi-layered, multi-protocol system. The goal
of this proposal is to reduce the number of protocols that need to
be deployed in order to get dynamic multicast address allocation.
The use of unicast prefix-based multicast address allocation will,
at a minimum, remove the need to run the Multicast Address
Allocation Protocol (AAP) [AAP WORK] and the Multicast Address-Set
Claim (MASC) Protocol [RFC 2909].
3. 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].
4. Multicast Address Format
Section 2.7 of [ADDRARCH] defines the following operational format
of IPv6 multicast addresses:
| 8 | 4 | 4 | 112 |
+--------+----+----+---------------------------------------------+
|11111111|flgs|scop| group ID |
+--------+----+----+---------------------------------------------+
This document introduces a new format that incorporates unicast
prefix information in the multicast address. The following
illustrates the new format:
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Internet Draft Unicast Prefix-based IPv6 Multicast October 2001
| 8 | 4 | 4 | 8 | 8 | 64 | 32 |
+--------+----+----+--------+--------+----------------+----------+
|11111111|flgs|scop|reserved| plen | network prefix | group ID |
+--------+----+----+--------+--------+----------------+----------+
+-+-+-+-+
flgs is a set of 4 flags: |0|0|P|T|
+-+-+-+-+
o P = 0 indicates a multicast address that is not assigned
based on the network prefix. This indicates a multicast
address as defined in [ADDRARCH].
o P = 1 indicates a multicast address that is assigned
based on the network prefix.
o If P = 1, T MUST be set to 1, otherwise the setting of
the T bit is defined in Section 2.7 of [ADDRARCH].
The reserved field MUST be zero.
plen indicates the actual number of bits in the network prefix field
that identify the subnet when P = 1.
network prefix identifies the network prefix of the unicast subnet
owning the multicast address. If P = 1, this field contains the
unicast network prefix assigned to the domain owning, or allocating,
the multicast address. All non-significant bits of the network
prefix field SHOULD be zero.
It should be noted that the Interface Identifier requirements in
Section 2.5.1 of [ADDRARCH] effectively restricts the length of the
unicast prefix to 64 bits, hence the network prefix portion of the
multicast address will be at most 64 bits.
Group ID is set based on the guidelines outlined in [IPV6 GID].
The scope of the unicast-prefix based multicast address MUST NOT
exceed the scope of the unicast prefix embedded in the multicast
address.
5. Address Lifetime
The lifetime of a unicast prefix-based multicast addresses SHOULD
NOT exceed the Valid Lifetime field in the Prefix Information
option, corresponding to the unicast prefix being used, contained in
the Neighbor Discovery Router Advertisement message [RFC 2461]. The
lifetime of the multicast address is needed to support the Abstract
API for Multicast Address Allocation [RFC 2771].
It should be noted that the unicast prefix's Valid Lifetime in the
Router Advertisement message does not indicate that the prefix will
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Internet Draft Unicast Prefix-based IPv6 Multicast October 2001
become invalid at the end of the lifetime. Rather, that value is
typically a constant until a renumbering event is scheduled after
which, the prefix does become invalid.
The use of unicast prefix-based multicast addresses after the
unicast prefix has become invalid may lead to operational problems.
For example, routers that perform policy checks comparing the
multicast prefix against the unicast prefix assigned to an AS may
discard the packet.
6. Source-Specific Multicast Addresses
The unicast prefix-based IPv6 multicast address format supports
Source-specific multicast addresses, as defined by [SSM ARCH]. To
accomplish is, a node MUST:
o Set P = 1.
o Set plen = 0.
o Set network prefix = 0.
These settings create an SSM range of FF3x::/32 (where 'x' is any
valid scope value). The source address field in the IPv6 header
identifies the owner of the multicast address.
7. Examples
The following are a few examples of the structure of unicast prefix-
based multicast addresses.
- Global prefixes - A network with a unicast prefix of
3FFE:FFFF:1::/48 would also have a unicast prefix-based
multicast prefix of FF3x:0030:3FFE:FFFF:0001::/96 (where
'x' is any valid scope).
- Link-local prefix - A network segment (e.g. a 10baseT
Ethernet) using the link-local prefix would also be able
to use the multicast prefix FF32:000A:FE80::/96.
- SSM - All IPv6 SSM multicast addresses will have the
format FF3x::/96.
8. Security Considerations
It is possible that the embedded unicast prefix can aid in
identifying the allocation domain of a given multicast address,
though an allocation domain choosing to avoid being traced has no
obstacles currently to creating addresses using a prefix not
assigned to it, or using a smaller scope embedded prefix.
Using source-specific multicast addresses can sometimes aid in the
prevention of denial-of-service attacks by arbitrary sources,
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Internet Draft Unicast Prefix-based IPv6 Multicast October 2001
although no guarantee is provided. A more in-depth discussion of
the security considerations for SSM can be found in [SSM ARCH].
9. References
[RFC 2026] S. Bradner, "The Internet Standards Process --
Revision 3", BCP 9, RFC 2026, October 1996.
[RFC 2460] S. Deering and R. Hinden, "Internet Protocol, Version 6
(IPv6) Specification", RFC 2460, December 1998.
[ADDRARCH] R. Hinden and S. Deering, "IP Version 6 Addressing
Architecture", Work In Progress, July 2001.
[RFC 2908] Thaler, D., Handley, M., and Estrin, D., "The Internet
Multicast Address Allocation Architecture", RFC 2908,
September 2000.
[AAP WORK] M. Handley and S. Hanna, "Multicast Address Allocation
Protocol (AAP)", Work In Progress.
[RFC 2909] P. Radoslavov, et al, " The Multicast Address-Set Claim
(MASC) Protocol", RFC 2909, September 2000.
[RFC 2119] S. Bradner, "Key words for use in RFCs to Indicate
Requirement Levels", RFC 2119, BCP14, March 1999.
[IPV6 GID] B. Haberman, "Dynamic Allocation Guidelines for IPv6
Multicast Addresses", Work In Progress, September 2001.
[RFC 2461] Narten, T., Nordmark, E., Simpson, W., "Neighbor
Discovery for IP Version 6 (IPv6)", RFC 2461, December
1998.
[RFC 2771] R. Finlayson, " An Abstract API for Multicast Address
Allocation", RFC 2771, February 2000.
[SSM ARCH] H. Holbrook and B. Cain, "Source-Specific Multicast
for IP", Work In Progress, March 2001.
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AuthorĘs Address
Brian Haberman
Nortel Networks
300 Perimeter Park
Morrisville, NC 27560
1-919-905-7484
haberman@nortelnetworks.com
Dave Thaler
Microsoft Corporation
One Microsoft Way
Redmond, WA 48105-6399
1-425-703-8835
dthaler@microsoft.com
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