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Network Working Group                                           D. MeyerRequest for Comments: 4608                                    R. RockellBCP: 120                                                     G. ShepherdCategory: Best Current Practice                              August 2006Source-Specific Protocol Independent Multicast in 232/8Status of This Memo   This document specifies an Internet Best Current Practices for the   Internet Community, and requests discussion and suggestions for   improvements.  Distribution of this memo is unlimited.Copyright Notice   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   the 232/8 range.Table of Contents1. Introduction ....................................................21.1. BCP, Experimental Protocols, and Normative References ......22. Operational practices in 232/8 ..................................42.1. Preventing Local Sources from Sending to Shared Tree .......4      2.2. Preventing Remote Sources from Being Learned/Joined           via MSDP ...................................................42.3. Preventing Receivers from Joining the Shared Tree ..........42.4. Preventing RPs as Candidates for 232/8 .....................53. Acknowledgements ................................................54. Security Considerations .........................................55. References ......................................................65.1. Normative References .......................................65.2. Informative References .....................................6Meyer, et al.            Best Current Practice                  [Page 1]

RFC 4608              Source-Specific PIM in 232/8           August 20061.  Introduction   Current Protocol Independent Multicast - Sparse Mode (PIM-SM)   [RFC4601] 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   [RFC3569] 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 Sparse Mode 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 RPs as candidates for 232/8      o  Prevent remote sources from being learned/joined via Multicast         Source Discovery Protocol (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   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 Inter-Domain Multicast Routing         (IDMR) working group produced as an inter-domain protocol.         However, the IDMR WG (or subsequently, the Border Gateway         Multicast Protocol (BGMP) WG) never produced a protocol that         could be deployed to replace MSDP.Meyer, et al.            Best Current Practice                  [Page 2]

RFC 4608              Source-Specific PIM in 232/8           August 2006      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 the amount of state you can advertise.      o  MSDP reached nearly 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 to move that document to         Experimental.  Although advancement of MSDP to Proposed         Standard was considered, for the reasons mentioned above, it         was immediately discarded.      o  The advent of protocols such as source-specific multicast and         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 that must be read for   one 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 [RFC4601] and MSDP [RFC3618] 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 inRFC 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 the document.Meyer, et al.            Best Current Practice                  [Page 3]

RFC 4608              Source-Specific PIM in 232/8           August 2006   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 inRFC 2119 [RFC2119].2.  Operational practices in 232/82.1.  Preventing Local Sources from Sending to Shared Tree   In order to eliminate the use of shared trees for groups in 232/8,   while maintaining coexistence with ASM in PIM-SM, the behavior of the   RP and/or the DR needs to be modified.  This can be accomplished by      -  preventing data for 232/8 groups from being sent encapsulated         to the RP by the DR,      -  preventing the RP from accepting registers for 232/8 groups         from the DR, and      -  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, and the last hop   router is responsible for sending (S,G) joins directly to the source.   To prevent propagation of SAs in the 232/8 range, an RP SHOULD      -  never originate an SA for any 232/8 groups, and      -  never accept or forward an SA for any 232/8 groups.2.3.  Preventing Receivers from Joining the Shared Tree   Local PIM domain practices need to be enforced to prevent local   receivers from joining the shared tree for 232/8 groups.  This can be   accomplished by      -  preventing DR from sending (*,G) joins for 232/8 groups, and      -  preventing RP from accepting (*,G) join for 232/8 groups.   However, within a local PIM domain, any last-hop router NOT   preventing (*,G) joins may trigger unwanted (*,G) state toward the RP   that intersects an existing (S,G) tree, allowing the receiver on the   shared tree to receive the data, which breaks the source-specificMeyer, et al.            Best Current Practice                  [Page 4]

RFC 4608              Source-Specific PIM in 232/8           August 2006   [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.2.4.  Preventing RPs as Candidates for 232/8   Because SSM does not require an RP, all RPs SHOULD NOT offer   themselves as candidates in the 232/8 range.  This can be   accomplished by      -  preventing RP/BSR from announcing in the 232/8 range,      -  preventing ALL routers from accepting RP delegations in the         232/8 range, and      -  precluding RP functionality on RP for the 232/8 range.   Note that in typical practice, RPs 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 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 for a more specific range).3.  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.4.  Security Considerations   This document describes operational practices that introduce no new   security issues to PIM-SM [RFC4601] in either or SSM [RFC3569] 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   messages themselves) on the source-specific service model.  CreatingMeyer, et al.            Best Current Practice                  [Page 5]

RFC 4608              Source-Specific PIM in 232/8           August 2006   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.  References5.1.  Normative References   [RFC4601] Fenner, B., Handley, M., Holbrook, H., and I. Kouvelas,             "Protocol Independent Multicast - Sparse Mode (PIM-SM):             Protocol Specification (Revised)",RFC 4601, August 2006.   [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate             Requirement Levels",BCP 14,RFC 2119, March 1997.   [RFC2026] Bradner, S., "The Internet Standards Process -- Revision             3",BCP 9,RFC 2026, October 1996.   [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 2003.5.2.  Informative References   [IANA]http://www.iana.org   [RFCED]http://www.rfc-editor.org/policy.htmlAuthors' Addresses   David Meyer   EMail: dmm@1-4-5.net   Robert Rockell   Sprint   EMail: rrockell@sprint.net   Greg Shepherd   Cisco   EMail: gjshep@gmail.comMeyer, et al.            Best Current Practice                  [Page 6]

RFC 4608              Source-Specific PIM in 232/8           August 2006Full Copyright Statement   Copyright (C) The Internet Society (2006).   This document is subject to the rights, licenses and restrictions   contained inBCP 78, and except as set forth therein, the authors   retain all their rights.   This document and the information contained herein are provided on an   "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS   OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET   ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED,   INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE   INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED   WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.Intellectual Property   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 inBCP 78 andBCP 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 athttp://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   ietf-ipr@ietf.org.Acknowledgement   Funding for the RFC Editor function is provided by the IETF   Administrative Support Activity (IASA).Meyer, et al.            Best Current Practice                  [Page 7]