Network Working Group Shepherd
Internet-Draft Cisco
Expires: December 16, 2006 Rockell
Sprint
Meyer
Cisco
June 14, 2006
Source-Specific Protocol Independent Multicast in 232/8
draft-ietf-mboned-ssm232-09
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Copyright (C) The Internet Society (2006).
Abstract
IP Multicast group addresses in the 232/8 (232.0.0.0 to
232.255.255.255) range are designated as source-specific multicast
destination addresses and are reserved for use by source-specific
multicast applications and protocols. This document defines
operational recommendations to ensure source-specific behavior within
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the 232/8 range.
Requirements Language
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 [RFC2119].
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. BCP, Experimental Protocols and Normative References . . . 3
2. Operational practices in 232/8 . . . . . . . . . . . . . . . . 4
2.1. Preventing local sources from sending to shared tree . . . 4
2.2. Preventing remote sources from being learned/joined
via MSDP . . . . . . . . . . . . . . . . . . . . . . . . . 5
2.3. Preventing receivers from joining the shared tree . . . . . 5
3. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 6
4. Security Considerations . . . . . . . . . . . . . . . . . . . . 6
5. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 6
6. References . . . . . . . . . . . . . . . . . . . . . . . . . . 7
6.1. Normative References . . . . . . . . . . . . . . . . . . . 7
6.2. Informative References . . . . . . . . . . . . . . . . . . 7
7. Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 8
8. Intellectual Property and Copyright Statements . . . . . . . . . . 9
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1. Introduction
Current PIM Sparse Mode (PIM-SM) [I-D.pim-sm-v2-new] relies on the
shared Rendezvous Point (RP) tree to learn about active sources for a
group and to support group-generic (Any Source Multicast or ASM) data
distribution. The IP Multicast group address range 232/8 has been
designated for Source-Specific Multicast (SSM) applications and
protocols [IANA] and SHOULD support source-only trees only,
precluding the requirement of an RP and a shared tree; active sources
in the 232/8 range will be discovered out of band. PIM-SM Designated
Routers (DR), with local membership, are capable of joining the
shortest path tree for the source directly using SSM functionality of
PIM-SM.
Operational best common practices in the 232/8 group address range
are necessary to ensure shortest path source-only trees across
multiple domains in the Internet [RFC3569], and to prevent data from
sources sending to groups in the 232/8 range from arriving via shared
trees. This avoids unwanted data arrival, and allows several sources
to use the same group address without conflict at the receivers.
The operational practices SHOULD: o Prevent local sources from
sending to shared tree o Prevent receivers from joining the shared
tree o Prevent RP's as candidates for 232/8 o Prevent remote sources
from being learned/joined via MSDP [RFC3618]
1.1. BCP, Experimental Protocols and Normative References
This document describes the best current practice for a widely
deployed Experimental protocol, MSDP. There is no plan to advance
the MSDP's status (for example, to Proposed Standard). The reasons
for this include:
o MSDP was originally envisioned as a temporary protocol to be
supplanted by whatever the IDMR working group produced as an
inter-domain protocol. However, the IDMR WG (or subsequently, the
BGMP WG) never produced a protocol that could be deployed to
replace MSDP.
o One of the primary reasons given for MSDP to be classified as
Experimental was that the MSDP Working Group came up with
modifications to the protocol that the WG thought made it better
but that implementors didn't see any reasons to deploy. Without
these modifications (e.g., UDP or GRE encapsulation), MSDP can
have negative consequences to initial packets in datagram streams.
o Scalability: Although we don't know what the hard limits might be,
readvertising everything you know every 60 seconds clearly limits
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the amount of state you can advertise.
o MSDP reached near ubiquitous deployment as the de-facto standard
inter-domain multicast protocol in the IPv4 Internet.
o No consensus could be reached regarding the reworking of MSDP to
address the many concerns of various constituencies within the
IETF. As a result, a decision was taken to document what is
(ubiquitously) deployed and move that document to Experimental.
While advancement of MSDP to Proposed Standard was considered, for
the reasons mentioned above, it was immediately discarded.
o The advent of source specific multicast and protocols such as bi-
directional PIM, as well as embedded RP techniques for IPv6, have
further reduced consensus that a replacement protocol for MSDP for
the IPv4 Internet is required.
The RFC Editor's policy regarding references is that they be split
into two categories known as "normative" and "informative".
Normative references specify those documents which must be read to
understand or implement the technology in an RFC (or whose technology
must be present for the technology in the new RFC to work) [RFCED].
In order to understand this document, one must also understand both
the PIM-SM and MSDP documents. As a result, references to these
documents are normative. The IETF has adopted the policy that BCPs
must not have normative references to Experimental protocols.
However, this document is a special case in that the underlying
Experimental document (MSDP) is not planned to be advanced to
Proposed Standard. The MBONED Working Group requests approval under
the Variance Procedure as documented in RFC 2026 [RFC2026]. Note to
RFC-Editor: If IETF/IESG approves this, please change the above
sentence into: The MBONED Working Group has requested approval under
the Variance Procedure as documented in RFC 2026 [RFC2026]. The IESG
followed the Variance Procedure, and after an additional 4 week IETF
Last Call evaluated the comments and status and has approved this
document.
2. Operational practices in 232/8
2.1. Preventing local sources from sending to shared tree
Eliminating the use of shared trees for groups in 232/8, while
maintaining coexistence with ASM in PIM-SM, behavior of the RP and/or
the DR needs to be modified. This can be accomplished by
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o preventing data for 232/8 groups from being sent encapsulated to
the RP by the DR.
o preventing the RP from accepting registers for 232/8 groups from
the DR.
o preventing the RP from forwarding accepted data down (*,G) tree
for 232/8 groups.
2.2. Preventing remote sources from being learned/joined via MSDP
SSM does not require active source announcements via MSDP. All
source announcements are received out of band, the the last hop
router being responsible for sending (S,G) joins directly to the
source. To prevent propagation of SAs in the 232/8 range, an RP
SHOULD
o never originate an SA for any 232/8 groups.
o never accept or forward an SA for any 232/8 groups.
2.3. Preventing receivers from joining the shared tree
Local PIM-SM domain practices need to be enforced to prevent local
receivers from joining the shared tree for 232/8 groups. This can be
accomplished by 232/8 range.
o preventing DR from sending (*,G) joins for 232/8 groups.
o preventing RP from accepting (*,G) join for 232/8 groups.
However, within a local PIM-SM domain, any last-hop router NOT
preventing (*,G) joins may trigger unwanted (*,G) state toward the RP
which intersects an existing (S,G) tree, allowing the receiver on the
shared tree to receive the data, breaking the source-specific
[RFC3569] service model. It is therefore recommended that ALL
routers in the domain MUST reject AND never originate (*,G) joins for
232/8 groups. In those cases in which an ISP is offering its
customers (or others) the use of the ISP's RP, the ISP SHOULD NOT
allow (*,G) joins in the 232/8 range.
Because SSM does not require a PIM-SM RP, all RPs SHOULD NOT offer
themselves as candidates in the 232/8 range. This can be
accomplished by
o preventing RP/BSR from announcing in the 232/8 range
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o preventing ALL routers from accepting RP delegations in the 232/8
range
o precluding RP functionality on RP for the 232/8 range
Note that in typical practice, RP's announce themselves as candidates
for the 224/4 (which obviously includes 232/8). It is still
acceptable to allow the advertisement of 224/4 (or any other superset
of 232/8); however, this approach relies on the second point, above,
namely, that routers silently just ignore the RP delegation in the
232/8 range, and prevent sending or receiving using the shared tree,
as described previously. Finally, an RP SHOULD NOT be configured as
a candidate RP for 232/8 (or more specific range).
3. IANA Considerations
This document creates no new requirements on IANA namespaces
[RFC2434].
4. Security Considerations
This document describes operational practices that introduce no new
security issues to PIM-SM in either SSM or ASM operation. However,
in the event that the operational practices described in this
document are not adhered to, some problems may surface. In
particular, section 2.3 describes the effects of non-compliance of
last-hop routers (or to some degree, rogue hosts sending PIM-SM
messages themselves) on the source-specific service model; creating
the (*,G) state for source-specific (S,G) could enable a receiver to
receive data it should not get. This can be mitigated by host-side
multicast source filtering.
5. Acknowledgements
This document is the work of many people in the multicast community,
including (but not limited to) Dino Farinacci, John Meylor, John
Zwiebel, Tom Pusateri, Dave Thaler, Toerless Eckert, Leonard
Giuliano, Mike McBride, and Pekka Savola.
6. References
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6.1. Normative References
[I-D.ietf-pim-sm-v2-new]
Fenner, B., "Protocol Independent Multicast - Sparse Mode
(PIM-SM): Protocol Specification (Revised)",
draft-ietf-pim-sm-v2-new-12 (work in progress),
March 2006.
[RFC2026] Bradner, S., "The Internet Standards Process -- Revision
3", BCP 9, RFC 2026, October 1996.
[RFC2028] Hovey, R. and S. Bradner, "The Organizations Involved in
the IETF Standards Process", BCP 11, RFC 2028,
October 1996.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2434] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 2434,
October 1998.
[RFC3569] Bhattacharyya, S., "An Overview of Source-Specific
Multicast (SSM)", RFC 3569, July 2003.
[RFC3618] Fenner, B. and D. Meyer, "Multicast Source Discovery
Protocol (MSDP)", RFC 3618, October 2003.
6.2. Informative References
[IANA] "http://www.iana.org", 2005.
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7. Authors' Addresses
Greg Shepherd
Cisco
Email: shep@cisco.com
Robert Rockell
Sprint
Email: rrockell@sprint.net
Dave Meyer
Cisco
Email: dmm@1-4-5.net
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8. Intellectual Property Statement
The IETF takes no position regarding the validity or scope of any
Intellectual Property Rights or other rights that might be claimed to
pertain to the implementation or use of the technology described in
this document or the extent to which any license under such rights
might or might not be available; nor does it represent that it has
made any independent effort to identify any such rights. Information
on the procedures with respect to rights in RFC documents can be
found in BCP 78 and BCP 79.
Copies of IPR disclosures made to the IETF Secretariat and any
assurances of licenses to be made available, or the result of an
attempt made to obtain a general license or permission for the use of
such proprietary rights by implementers or users of this
specification can be obtained from the IETF on-line IPR repository at
http://www.ietf.org/ipr.
The IETF invites any interested party to bring to its attention any
copyrights, patents or patent applications, or other proprietary
rights that may cover technology that may be required to implement
this standard. Please address the information to the IETF at
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Disclaimer of Validity
This document and the information contained herein are provided on an
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Copyright Statement
Copyright (C) The Internet Society (2006). This document is subject
to the rights, licenses and restrictions contained in BCP 78, and
except as set forth therein, the authors retain all their rights.
Acknowledgment
Funding for the RFC Editor function is currently provided by the
Internet Society.
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