draft-ietf-mboned-ipv4-uni-based-mcast-04.txt   draft-ietf-mboned-ipv4-uni-based-mcast-05.txt 
Network Working Group D. Thaler Network Working Group D. Thaler
Internet-Draft Microsoft Internet-Draft Microsoft
Expires: January 27, 2008 July 26, 2007 Expires: August 28, 2008 February 25, 2008
Unicast-Prefix-based IPv4 Multicast Addresses Unicast-Prefix-based IPv4 Multicast Addresses
draft-ietf-mboned-ipv4-uni-based-mcast-04.txt draft-ietf-mboned-ipv4-uni-based-mcast-05.txt
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This Internet-Draft will expire on January 27, 2008. This Internet-Draft will expire on August 28, 2008.
Copyright Notice Copyright Notice
Copyright (C) The IETF Trust (2007). Copyright (C) The IETF Trust (2008).
Abstract Abstract
This specification defines an extension to the multicast addressing This specification defines an extension to the multicast addressing
architecture of the IP Version 4 protocol. The extension presented architecture of the IP Version 4 protocol. The extension presented
in this document allows for unicast-prefix-based allocation of in this document allows for unicast-prefix-based assignment of
multicast addresses. By delegating multicast addresses at the same multicast addresses. By delegating multicast addresses at the same
time as unicast prefixes, network operators will be able to identify time as unicast prefixes, network operators will be able to identify
their multicast addresses without needing to run an inter-domain their multicast addresses without needing to run an inter-domain
allocation protocol. allocation protocol.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Address Space . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Security Considerations . . . . . . . . . . . . . . . . . . . . 4 3. Address Space . . . . . . . . . . . . . . . . . . . . . . . . . 4
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 4 4. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
5. Informative References . . . . . . . . . . . . . . . . . . . . 5 5. Security Considerations . . . . . . . . . . . . . . . . . . . . 5
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 5 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 5
Intellectual Property and Copyright Statements . . . . . . . . . . 6 7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . 5
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 6
8.1. Normative References . . . . . . . . . . . . . . . . . . . 6
8.2. Informative References . . . . . . . . . . . . . . . . . . 6
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 6
Intellectual Property and Copyright Statements . . . . . . . . . . 7
1. Introduction 1. Introduction
RFC 3180 [RFC3180] defined an experimental allocation mechanism RFC 3180 [RFC3180] defined an experimental allocation mechanism
(called "GLOP") in 233/8 whereby an Autonomous System (AS) number is (called "GLOP") in 233/8 whereby an Autonomous System (AS) number is
embedded in the middle 16 bits of an IPv4 multicast address, embedded in the middle 16 bits of an IPv4 multicast address,
resulting in 256 multicast addresses per AS. Advantages of this resulting in 256 multicast addresses per AS. Advantages of this
mechanism include the ability to get multicast address space without mechanism include the ability to get multicast address space without
an inter-domain multicast address allocation protocol, and the ease an inter-domain multicast address allocation protocol, and the ease
of determining the AS of the owner of an address for debugging and of determining the AS that was assigned the address for debugging and
auditing purposes. auditing 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 MADCAP
[RFC2730]. [RFC2730].
o During debugging, identifying the AS does not immediately identify o During debugging, identifying the AS does not immediately identify
the owning 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
than just to an entire AS, is that multicast address allocation than just to an entire AS, is that multicast address assignment
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 draft specifies a mechanism similar to [RFC3306], whereby a
range of 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 proposes an experimental method of statically 2. Terminology
allocating multicast address ranges with global scope. As described
in section Section 4, this experiment will last for a period of one
year, but may be extended.
2. Address Space 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].
(RFC-editor: replace TBD below with IANA-assigned value, and delete 3. Address Space
this note.)
(RFC-editor: replace TBD in this section and the next with IANA-
assigned value, and delete this note.)
A multicast address with the prefix TBD/8 indicates that the address 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: | 8 | Unicast Prefix Length | 24 - Unicast Prefix Length |
+-----+-----------------------+----------------------------+ +-----+-----------------------+----------------------------+
Value: | TBD | Unicast Prefix | Group ID | Value: | TBD | 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. For may be assigned by any mechanism the organization wishes.
example, an organization that has a subnet with a /24 or shorter
prefix assigned to a link may wish to embed the entire subnet prefix For example, an organization that has a /16 prefix assigned might
within the multicast address, with the remaining bits assigned by choose to assign multicast addresses manually from the /24 multicast
hosts within the link (e.g., using manual configuration). prefix derived from the above method. Alternatively, the
organization might choose to delegate the use of multicast addresses
to individual subnets that have a /24 or shorter unicast prefix, or
it might choose some other method.
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 owner of a UBM address can be determined by taking the multicast The organization that is assigned the UBM address can be determined
address, shifting it left by 8 bits, and identifying the owner of the by taking the multicast address, shifting it left by 8 bits, and
address space covering the resulting unicast address. identifying who has been assigned the address space covering the
resulting unicast address.
3. Security Considerations The embedded unicast prefix MUST be a global unicast prefix (i.e., no
loopback, multicast, link-local, or private-use IP address space).
In addition, since global unicast addresses are not permanently
assigned, UBM addresses MUST NOT be hard-coded in applications.
4. Examples
The following are a few examples of the structure of unicast-prefix
based multicast addresses.
o Consider an organization that has been assigned the global unicast
address space 192.0.2.0/24. This means that organization can use
the global multicast address TBD.192.0.2 without coordinating with
any other entity. Someone who sees this multicast address and
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
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
address space TBD.x.y.0/24 without coordinating with any other
entity, and can assign addresses within this space by any
mechanism the organization wishes. Someone who sees a multicast
address (say) TBD.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
then look up who has been assigned unicast address space that
includes that address.
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 space 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.
4. IANA Considerations 6. IANA Considerations
IANA should assign a /8 in the IPv4 multicast address space for this IANA should assign a /8 in the global IPv4 multicast address space
purpose. for this purpose.
This assignment should time out one year after the assignment is 7. Acknowledgments
made. The assignment may be renewed at that time.
5. Informative References This document was updated based on feedback from the MBoneD working
group. In particular, Tim Chown, Toerless Eckert, Prashant Jhingran,
Peter Koch, John Linn, Dave Meyer, Pekka Savola, Greg Shepherd, and
Stig Venaas provided valuable suggestions on the text.
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.
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.
[RFC3180] Meyer, D. and P. Lothberg, "GLOP Addressing in 233/8", [RFC3180] Meyer, D. and P. Lothberg, "GLOP Addressing in 233/8",
BCP 53, RFC 3180, September 2001. BCP 53, RFC 3180, September 2001.
[RFC3306] Haberman, B. and D. Thaler, "Unicast-Prefix-based IPv6 [RFC3306] Haberman, B. and D. Thaler, "Unicast-Prefix-based IPv6
Multicast Addresses", RFC 3306, August 2002. Multicast Addresses", RFC 3306, August 2002.
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Email: dthaler@microsoft.com Email: dthaler@microsoft.com
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Copyright (C) The IETF Trust (2007). Copyright (C) The IETF Trust (2008).
This document is subject to the rights, licenses and restrictions This document is subject to the rights, licenses and restrictions
contained in BCP 78, and except as set forth therein, the authors contained in BCP 78, and except as set forth therein, the authors
retain all their rights. retain all their rights.
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