One document matched: draft-haberman-ipngwg-mcast-arch-01.txt
Differences from draft-haberman-ipngwg-mcast-arch-00.txt
IPNGWG Working Group B. Haberman
Internet Draft Nortel Networks
draft-haberman-ipngwg-mcast-arch-01.txt D. Thaler
March 2000 Microsoft
Expires September 2000
IP Version 6 Multicast Addressing Architecture
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-Drafts. Internet-
Drafts are draft documents valid for a maximum of six months and may be
updated, replaced, or obsoleted by other 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
http://www.ietf.org/shadow.html.
Abstract
This specification defines the multicast addressing architecture of the
IP Version 6 protocol. The updated multicast address architecture
presented in this document allows for unicast prefix-based allocation
of multicast addresses. It is an update of section 2.7 of the RFC
2373.
1. Introduction
This document specifies an update to the IPv6 multicast addressing
architecture [RFC 2373]. 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, network prefix-based allocation of IPv6 multicast addresses,
as well as allocation of single-source multicast addresses.
2. Multicast Address Format
An IPv6 multicast address is an identifier for a group of nodes. A
node may belong to any number of multicast groups. Multicast addresses
have the following generic format:
| 8 | 4 | 4 | 80 | 32 |
+--------+----+----+-----------------------------------+------------+
|11111111|flgs|scop| (see below) | group ID |
+--------+----+----+-----------------------------------+------------+
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11111111 at the start of the address identifies the address as being a
multicast address.
+-+-+-+-+
flgs is a set of 4 flags: |0|S|P|T|
+-+-+-+-+
o The high-order flag is reserved, and must be initialized to
0.
o P = 0 indicates a multicast address that is not assigned
based on the network prefix.
o P = 1 indicates a multicast address that is assigned based
on the network prefix.
o T = 0 indicates a permanently assigned ("well-known")
multicast address, assigned by the global Internet numbering
authority.
o T = 1 indicates a non-permanently-assigned ("transient")
multicast address.
o S = 0 indicates a multicast address that is not a single-
source group address.
o S = 1 indicates a multicast address that is a single-source
group address.
scop is a 4-bit multicast scope value used to limit the scope of the
multicast group. The values are:
0 reserved
1 node-local scope
2 link-local scope
3 local scope
4 (unassigned)
5 site-local scope
6 allocation scope
7 (unassigned)
8 organization-local scope
9 (unassigned)
A (unassigned)
B (unassigned)
C (unassigned)
D (unassigned)
E global scope
F reserved
The format of the next 80 bits is dependent on the value of the flags,
and is discussed in Section 4 below.
group ID identifies the multicast group, either permanent or transient,
within the given scope.
The "meaning" of a permanently assigned multicast address is
independent of the scope value. For example, if the "NTP servers
group" is assigned a permanent multicast address with a group ID of 101
(hex), then:
FF01::101 means all NTP servers on the same node as the sender.
FF02::101 means all NTP servers on the same link as the sender.
FF05::101 means all NTP servers in the same site as the sender.
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FF0E::101 means all NTP servers in the Internet.
Non-permanently-assigned multicast addresses are meaningful only within
a given scope. For example, a group identified by the non-permanent,
site-local multicast address FF15::101 at one site bears no
relationship to a group using the same address at a different site, or
to a non-permanent group using the same group ID with a different
scope, nor to a permanent group with the same group ID.
Multicast addresses must not be used as source addresses in IPv6
packets or appear in any routing header.
3. Pre-Defined Multicast Addresses
Since the meaning of a permanently assigned multicast address is
independent of the scope value, such addresses are valid over all scope
ranges. This is shown by an "x" in the scope field of the address that
means any legal scope value.
Note that multicast addresses that differ only in scope represent
different groups. Nodes must join each group individually.
The following well-known multicast addresses are pre-defined:
Reserved Multicast Addresses: FF0x:0:0:0:0:0:0:0
The above multicast addresses are reserved and shall never be assigned
to any multicast group.
All Nodes Addresses: FF0x:0:0:0:0:0:0:1
The above multicast addresses identify the group of all IPv6 nodes
within a given scope. The All-Nodes-Address for scopes larger than
scope 2 (link-local) SHOULD NOT be used or joined by nodes.
All Routers Addresses: FF0x:0:0:0:0:0:0:2
The above multicast addresses identify the group of all IPv6 routers
within a given scope. The All-Routers-Address for scopes other than
scope 1 (node-local), 2 (link-local), and 5 (site-local) SHOULD NOT be
used or joined by routers.
Solicited-Node Address: FF0x:0:0:0:0:1:FFXX:XXXX
The above multicast address is computed as a function of a node's
unicast and anycast addresses, and SHOULD NOT be used or joined for any
scope value other than scope 2 (link-local). The solicited-node
multicast address is formed by taking the low-order 24 bits of the
address (unicast or anycast) and appending those bits to the prefix
FF02:0:0:0:0:1:FF00::/104 resulting in a multicast address in the range
FF02:0:0:0:0:1:FF00:0000 to FF02:0:0:0:01:FFFF:FFFF.
For example, the solicited node multicast address corresponding to the
IPv6 address 4037::01:800:200E:8C6C is FF02::1:FF0E:8C6C. IPv6
addresses that differ only in the high-order bits, e.g. due to multiple
high-order prefixes associated with different aggregations, will map to
the same solicited-node address thereby reducing the number of
multicast addresses a node must join.
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A node is required to compute and join the associated Solicited-Node
multicast addresses for every unicast and anycast address it is
assigned.
4. Assignment of New IPv6 Multicast Addresses
The current approach [RFC 2464] to map IPv6 multicast addresses into
IEEE 802 MAC addresses takes the low order 32 bits of the IPv6
multicast address and uses it to create a MAC address. Note that Token
Ring networks are handled differently. Token Ring support of IPv6
multicast is defined in [RFC 2470]. Group ID's less than or equal to
32 bits long will generate unique MAC addresses.
Due to this, the existing IPv6 multicast address architecture suggests
that the group identifier always be in the low order 32 bits as shown
in the following:
| 8 | 4 | 4 | 80 bits | 32 bits |
+--------+----+----+----------------------------+-------------------+
|11111111|flgs|scop| reserved must be zero | group ID |
+--------+----+----+----------------------------+-------------------+
This document updates the above by specifying a different address
format when P = 1. Any new IPv6 multicast addresses that are network
prefix-based will have the following format:
| 8 | 4 | 4 | 8 | plen |72 - plen | 32 |
+--------+----+----+-------+----------------+----------+------------+
|11111111|flgs|scop| plen | network prefix | reserved | group ID |
+--------+----+----+-------+----------------+----------+------------+
plen indicates the length of the network prefix portion of the address
when P = 1. This field is required in order to determine the number of
bits to include as part of the unicast prefix.
network prefix identifies the network prefix of the unicast subnet
owning the multicast address. If P = 1, this field contains the
unicast network prefix defined in [RFC 2374] and assigned to the domain
owning the multicast address.
The reserved field must be zero.
While this limits the number of unicast prefix-based IPv6 multicast
groups to 2^32 per prefix, this is unlikely to be a limitation in the
future. If it becomes necessary to exceed this limit in the future,
multicast will still work but the processing will be slightly slower.
With the network prefix-based architecture and the current unicast
address architecture [RFC 2374], the network prefix portion of the
multicast address will be at most 64 bits. This allows for the group
ID field to be at least 40 bits.
Additional IPv6 multicast addresses are defined and registered by the
IANA [RFC 2375].
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5. Open Issues
5.1 IPv4-compatible Multicast Addresses
Is ::224.1.2.24 considered a legal IPv6 multicast address? Is
::FFFF:224.1.2.24 considered a legal IPv6 multicast address?
5.2 Scope-relative Offsets
Scope-relative offsets as described in RFC 2365 [RFC 2365] are defined
with language implying the offset is the same between IPv6 and IPv4.
IANA has assigned them from separate number spaces. Should these
offsets be the same for IPv4 and IPv6 so that every protocol that wants
a scope-relative offset only has to get one offset and not two?
6. Security Considerations
Using unicast network-prefix based multicast addresses can sometimes
aid in identifying the allocation domain of a given multicast address,
although no guarantee is provided.
Using single-source multicast addresses can sometimes aid in the
prevention of denial-of-service attacks by arbitrary sources, although
no guarantee is provided.
7. 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.
[RFC 2373] R. Hinden and S. Deering, "IP Version 6 Addressing
Architecture", RFC 2373, July 1998.
[RFC 2119] S. Bradner, "Key words for use in RFCs to Indicate
Requirement Levels", RFC 2119, BCP14, March 1999.
[RFC 2374] R. Hinden, M. O'Dell, and S. Deering, "An IPv6
Aggregatable Global Unicast Address Format", RFC 2374,
July 1998.
[RFC 2464] M. Crawford, "Transmission of IPv6 Packets over Ethernet
Networks", RFC 2464, December 1998.
[RFC 2470] M. Crawford, T. Narten, and S. Thomas, "Transmission of IPv6
Packets over Token Ring Networks", RFC 2470, December 1998.
[RFC 2375] R. Hinden and S. Deering, "IPv6 Multicast Address
Assignments", RFC 2375, July 1998.
[RFC 2365] D. Meyer, "Administratively Scoped IP Multicast",
BCP 23, RFC 2365, July 1998.
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Author's Address
Brian Haberman
Nortel Networks
4309 Emperor Blvd.
Suite 200
Durham, NC 27703
1-919-992-4439
Email : haberman@nortelnetworks.com
Dave Thaler
Microsoft Corporation
One Microsoft Way
Redmond, WA 48105-6399
1-425-703-8835
Email: dthaler@microsoft.com
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