draft-ietf-mboned-ipv4-uni-based-mcast-06.txt   rfc6034.txt 
Network Working Group D. Thaler Internet Engineering Task Force (IETF) D. Thaler
Internet-Draft Microsoft Request for Comments: 6034 Microsoft
Expires: September 10, 2009 March 9, 2009 Category: Standards Track October 2010
ISSN: 2070-1721
Unicast-Prefix-based IPv4 Multicast Addresses
draft-ietf-mboned-ipv4-uni-based-mcast-06.txt
Status of this Memo Unicast-Prefix-Based IPv4 Multicast Addresses
This Internet-Draft is submitted to IETF in full conformance with the Abstract
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering This specification defines an extension to the multicast addressing
Task Force (IETF), its areas, and its working groups. Note that architecture of the IP Version 4 protocol. The extension presented
other groups may also distribute working documents as Internet- in this document allows for unicast-prefix-based assignment of
Drafts. 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.
Internet-Drafts are draft documents valid for a maximum of six months Status of This Memo
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 This is an Internet Standards Track document.
http://www.ietf.org/ietf/1id-abstracts.txt.
The list of Internet-Draft Shadow Directories can be accessed at This document is a product of the Internet Engineering Task Force
http://www.ietf.org/shadow.html. (IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 5741.
This Internet-Draft will expire on September 10, 2009. Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc6034.
Copyright Notice Copyright Notice
Copyright (c) 2009 IETF Trust and the persons identified as the Copyright (c) 2010 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents in effect on the date of Provisions Relating to IETF Documents
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Please review these documents carefully, as they describe your rights publication of this document. Please review these documents
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to this document. Code Components extracted from this document must
Abstract include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
This specification defines an extension to the multicast addressing described in the Simplified BSD License.
architecture of the IP Version 4 protocol. The extension presented
in this document allows for unicast-prefix-based assignment 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 Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Address Space . . . . . . . . . . . . . . . . . . . . . . . . . 4 3. Address Space . . . . . . . . . . . . . . . . . . . . . . . . . 3
4. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 4. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
5. Security Considerations . . . . . . . . . . . . . . . . . . . . 5 5. Security Considerations . . . . . . . . . . . . . . . . . . . . 4
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 5 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 5
7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . 5 7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . 5
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 6 8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 5
8.1. Normative References . . . . . . . . . . . . . . . . . . . 6 8.1. Normative References . . . . . . . . . . . . . . . . . . . 5
8.2. Informative References . . . . . . . . . . . . . . . . . . 6 8.2. Informative References . . . . . . . . . . . . . . . . . . 5
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 6
1. Introduction 1. Introduction
RFC 3180 [RFC3180] defined an experimental allocation mechanism RFC 3180 [RFC3180] defines an allocation mechanism (called "GLOP") in
(called "GLOP") in 233/8 whereby an Autonomous System (AS) number is 233/8 whereby an Autonomous System (AS) number is embedded in the
embedded in the middle 16 bits of an IPv4 multicast address, middle 16 bits of an IPv4 multicast address, resulting in 256
resulting in 256 multicast addresses per AS. Advantages of this multicast addresses per AS. Advantages of this mechanism include the
mechanism include the ability to get multicast address space without ability to get multicast address space without an inter-domain
an inter-domain multicast address allocation protocol, and the ease multicast address allocation protocol, and the ease of determining
of determining the AS that was assigned the address for debugging and the AS that was assigned the address for debugging and auditing
auditing purposes. purposes.
Some disadvantages of GLOP include: Some disadvantages of GLOP include:
o RFC 4893 [RFC4893] expands the size of an AS number to 4 bytes, o RFC 4893 [RFC4893] expands the size of an AS number to 4 bytes,
and GLOP cannot work with 4-byte AS numbers. and GLOP cannot work with 4-byte AS numbers.
o When an AS covers multiple sites or organizations, administration o When an AS covers multiple sites or organizations, administration
of the multicast address space within an AS must be handled by of the multicast address space within an AS must be handled by
other mechanisms, such as manual administrative effort or MADCAP other mechanisms, such as manual administrative effort or the
Multicast Address Dynamic Client Allocation Protocol (MADCAP)
[RFC2730]. [RFC2730].
o During debugging, identifying the AS does not immediately identify o During debugging, identifying the AS does not immediately identify
the correct organization when an AS covers multiple organizations. the correct organization when an AS covers multiple organizations.
o Only 256 addresses are automatically available per AS, and o Only 256 addresses are automatically available per AS, and
obtaining any more requires administrative effort. obtaining any more requires administrative effort.
More recently, a mechanism [RFC3306] has been developed for IPv6 that More recently, a mechanism [RFC3306] has been developed for IPv6 that
provides a multicast range to every IPv6 subnet, which is at a much provides a multicast range to every IPv6 subnet, which is at a much
finer granularity than an AS. As a result, the first three finer granularity than an AS. As a result, the first three
disadvantages above are avoided (and the last disadvantage does not disadvantages above are avoided (and the last disadvantage does not
apply to IPv6 due to the extended size of the address space). apply to IPv6 due to the extended size of the address space).
Another advantage of providing multicast space to a subnet, rather Another advantage of providing multicast space to a subnet, rather
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o Only 256 addresses are automatically available per AS, and o Only 256 addresses are automatically available per AS, and
obtaining any more requires administrative effort. obtaining any more requires administrative effort.
More recently, a mechanism [RFC3306] has been developed for IPv6 that More recently, a mechanism [RFC3306] has been developed for IPv6 that
provides a multicast range to every IPv6 subnet, which is at a much provides a multicast range to every IPv6 subnet, which is at a much
finer granularity than an AS. As a result, the first three finer granularity than an AS. As a result, the first three
disadvantages above are avoided (and the last disadvantage does not disadvantages above are avoided (and the last disadvantage does not
apply to IPv6 due to the extended size of the address space). apply to IPv6 due to the extended size of the address space).
Another advantage of providing multicast space to a subnet, rather Another advantage of providing multicast space to a subnet, rather
than just to an entire AS, is that multicast address assignment than just to an entire AS, is that multicast address assignments
within the range need only be coordinated within the subnet. within the range need only be coordinated within the subnet.
This draft specifies a mechanism similar to [RFC3306], whereby a This document specifies a mechanism similar to [RFC3306], whereby a
range of global IPv4 multicast address space is provided to each range of global IPv4 multicast address space is provided to each
organization that has unicast address space. A resulting advantage organization that has unicast address space. A resulting advantage
over GLOP is that the mechanisms in IPv4 and IPv6 become more over GLOP is that the mechanisms in IPv4 and IPv6 become more
similar. similar.
This document does not obsolete or update RFC 3180, as the mechanism
described in RFC 3180 is still required for organizations with prefix
allocations more specific than /24. Organizations using RFC 3180
allocations may continue to do so. In fact, it is conceivable that
an organization might use both RFC 3180 allocations and the
allocation method described in this document.
2. Terminology 2. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119]. document are to be interpreted as described in [RFC2119].
3. Address Space 3. Address Space
(RFC-editor: replace TBD in this section and the next with IANA- A multicast address with the prefix 234/8 indicates that the address
assigned value, and delete this note.)
A multicast address with the prefix TBD/8 indicates that the address
is a Unicast-Based Multicast (UBM) address. The remaining 24 bits is a Unicast-Based Multicast (UBM) address. The remaining 24 bits
are used as follows: are used as follows:
Bits: | 8 | Unicast Prefix Length | 24 - Unicast Prefix Length | Bits: | 0 thru 7 | 8 thru N | N+1 thru 31 |
+-----+-----------------------+----------------------------+ +-------+--------------------+-----------------------------+
Value: | TBD | Unicast Prefix | Group ID | Value: | 234 | Unicast Prefix | Group ID |
+-----+-----------------------+----------------------------+ +-------+--------------------+-----------------------------+
For organizations with a /24 or shorter prefix, the unicast prefix of For organizations with a /24 or shorter prefix, the unicast prefix of
the organization is appended to the common /8. Any remaining bits the organization is appended to the common /8. Any remaining bits
may be assigned by any mechanism the organization wishes. may be assigned by any mechanism the organization wishes.
For example, an organization that has a /16 prefix assigned might For example, an organization that has a /16 prefix assigned might
choose to assign multicast addresses manually from the /24 multicast choose to assign multicast addresses manually from the /24 multicast
prefix derived from the above method. Alternatively, the prefix derived from the above method. Alternatively, the
organization might choose to delegate the use of multicast addresses organization might choose to delegate the use of multicast addresses
to individual subnets that have a /24 or shorter unicast prefix, or to individual subnets that have a /24 or shorter unicast prefix, or
skipping to change at page 4, line 39 skipping to change at page 4, line 10
Organizations with a prefix length longer than 24 do not receive any Organizations with a prefix length longer than 24 do not receive any
multicast address space from this mechanism; in such cases, another multicast address space from this mechanism; in such cases, another
mechanism must be used. mechanism must be used.
Compared to GLOP, an AS will receive more address space via this Compared to GLOP, an AS will receive more address space via this
mechanism if it has more than a /16 for unicast space. An AS will mechanism if it has more than a /16 for unicast space. An AS will
receive less address space than it does from GLOP if it has less than receive less address space than it does from GLOP if it has less than
a /16. a /16.
The organization that is assigned the UBM address can be determined The organization that is assigned a UBM address can be determined by
by taking the multicast address, shifting it left by 8 bits, and taking the multicast address, shifting it left by 8 bits, and
identifying who has been assigned the address space covering the identifying who has been assigned the address space covering the
resulting unicast address. resulting unicast address.
The embedded unicast prefix MUST be a global unicast prefix (i.e., no The embedded unicast prefix MUST be a global unicast prefix (i.e., no
loopback, multicast, link-local, or private-use IP address space). loopback, multicast, link-local, or private-use IP address space).
In addition, since global unicast addresses are not permanently In addition, since global unicast addresses are not permanently
assigned, UBM addresses MUST NOT be hard-coded in applications. assigned, UBM addresses MUST NOT be hard-coded in applications.
4. Examples 4. Examples
The following are a few examples of the structure of unicast-prefix The following are a few examples of the structure of unicast-prefix-
based multicast addresses. based multicast addresses.
o Consider an organization that has been assigned the global unicast o Consider an organization that has been assigned the global unicast
address space 192.0.2.0/24. This means that organization can use address space 192.0.2.0/24. This means that organization can use
the global multicast address TBD.192.0.2 without coordinating with the global multicast address 234.192.0.2 without coordinating with
any other entity. Someone who sees this multicast address and any other entity. Someone who sees this multicast address and
wants to find who is using it can mentally shift the address left wants to find who is using it can mentally shift the address left
by 8 bits to get 192.0.2.0, and then look up who has been assigned by 8 bits to get 192.0.2.0, and can then look up who has been
unicast address space that includes that address. assigned unicast address space that includes that address.
o Consider an organization has been assigned a larger address space,
x.y.0.0/16. This organization can use the global multicast o Consider an organization that has been assigned a larger address
address space TBD.x.y.0/24 without coordinating with any other space, x.y.0.0/16. This organization can use the global multicast
address space 234.x.y.0/24 without coordinating with any other
entity, and can assign addresses within this space by any entity, and can assign addresses within this space by any
mechanism the organization wishes. Someone who sees a multicast mechanism the organization wishes. Someone who sees a multicast
address (say) TBD.x.y.10, and wants to find who is using it can address (say) 234.x.y.10 and wants to find who is using it can
mentally shift the address left by 8 bits to get x.y.10.0, and can mentally shift the address left by 8 bits to get x.y.10.0, and can
then look up who has been assigned unicast address space that then look up who has been assigned unicast address space that
includes that address. includes that address.
5. Security Considerations 5. Security Considerations
The same well known intra-domain security techniques can be applied The same well-known intra-domain security techniques can be applied
as with GLOP. Furthermore, when dynamic allocation is used within a as with GLOP. Furthermore, when dynamic allocation is used within a
prefix, the approach described here may have the effect of reduced prefix, the approach described here may have the effect of reduced
exposure to denial of space attacks, since the topological area exposure to denial-of-service attacks, since the topological area
within which nodes compete for addresses within the same prefix is within which nodes compete for addresses within the same prefix is
reduced from an entire AS to only within an individual organization reduced from an entire AS to only within an individual organization
or an even smaller area. or an even smaller area.
6. IANA Considerations 6. IANA Considerations
IANA should assign a /8 in the global IPv4 multicast address space IANA has assigned a /8 in the global IPv4 multicast address space for
for this purpose. this purpose.
7. Acknowledgments 7. Acknowledgments
This document was updated based on feedback from the MBoneD working This document was updated based on feedback from the MBoneD working
group. In particular, Tim Chown, Toerless Eckert, Prashant Jhingran, group. In particular, Tim Chown, Toerless Eckert, Prashant Jhingran,
Peter Koch, John Linn, Dave Meyer, Pekka Savola, Greg Shepherd, and Peter Koch, John Linn, Dave Meyer, Pekka Savola, Greg Shepherd, and
Stig Venaas provided valuable suggestions on the text. Stig Venaas provided valuable suggestions on the text.
8. References 8. References
8.1. Normative References 8.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997. Requirement Levels", BCP 14, RFC 2119, March 1997.
8.2. Informative References 8.2. Informative References
[RFC2730] Hanna, S., Patel, B., and M. Shah, "Multicast Address [RFC2730] Hanna, S., Patel, B., and M. Shah, "Multicast Address
Dynamic Client Allocation Protocol (MADCAP)", RFC 2730, Dynamic Client Allocation Protocol (MADCAP)", RFC 2730,
December 1999. December 1999.
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Author's Address Author's Address
Dave Thaler Dave Thaler
Microsoft Corporation Microsoft Corporation
One Microsoft Way One Microsoft Way
Redmond, WA 98052 Redmond, WA 98052
USA USA
Phone: +1 425 703 8835 Phone: +1 425 703 8835
Email: dthaler@microsoft.com EMail: dthaler@microsoft.com
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