Network Working Group D. Meyer Request for Comments: 4608 R. Rockell BCP: 120 G. Shepherd Category: Best Current Practice August 2006 Source-Specific Protocol Independent Multicast in 232/8 Status 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).
AbstractIP Multicast group addresses in the 232/8 (220.127.116.11 to 18.104.22.168) 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. 1. Introduction ....................................................2 1.1. BCP, Experimental Protocols, and Normative References ......2 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 ...................................................4 2.3. Preventing Receivers from Joining the Shared Tree ..........4 2.4. Preventing RPs as Candidates for 232/8 .....................5 3. Acknowledgements ................................................5 4. Security Considerations .........................................5 5. References ......................................................6 5.1. Normative References .......................................6 5.2. Informative References .....................................6
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]
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 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 the document.
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].
[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. 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. 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. [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. [IANA] http://www.iana.org [RFCED] http://www.rfc-editor.org/policy.html
Full 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. 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 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 email@example.com. Acknowledgement Funding for the RFC Editor function is provided by the IETF Administrative Support Activity (IASA).