PIM Working Group B. Joshi Internet-Draft Infosys Technologies Ltd. Expires: August 16, 2008 A. Kessler Cisco Systems, Inc. D. McWalter Data Connection Ltd February 13, 2008 PIM Group-to-RP Mapping draft-joshi-pim-group-rp-mapping-00.txt Status of this Memo By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or she is aware have been or will be disclosed, and any of which he or she becomes aware will be disclosed, in accordance with Section 6 of BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. Internet-Drafts are draft documents valid for a maximum of six months 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 http://www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on August 16, 2008. Copyright Notice Copyright (C) The IETF Trust (2008). Abstract Each PIM-SM router in a PIM Domain which supports ASM maintains Group-to-RP mappings which are used to identify a RP for a specific multicast group. PIM-SM has defined an algorithm to choose a RP from the Group-to-RP mappings learned using various mechanisms. This algorithm does not allow administrator to override a specific Group- Joshi, et al. Expires August 16, 2008 [Page 1] Internet-Draft PIM Group-to-RP Mapping February 2008 to-RP mapping with the static Group-to-RP mapping which an administrator would want to use. This algorithm also does not consider the PIM mode and the mechanism through which a Group-to-RP mapping was learned. This document first explains the requirements to extend the Group-to-RP mapping algorithm and then proposes the new algorithm. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 3. Existing algorithm . . . . . . . . . . . . . . . . . . . . . . 5 4. Assumptions . . . . . . . . . . . . . . . . . . . . . . . . . 6 5. Proposed algorithm . . . . . . . . . . . . . . . . . . . . . . 7 6. Deprecation of MIB Objects . . . . . . . . . . . . . . . . . . 9 7. Security Consideration . . . . . . . . . . . . . . . . . . . . 10 8. IANA Consideration . . . . . . . . . . . . . . . . . . . . . . 11 9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 12 10. Normative References . . . . . . . . . . . . . . . . . . . . . 12 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 13 Intellectual Property and Copyright Statements . . . . . . . . . . 14 Joshi, et al. Expires August 16, 2008 [Page 2] Internet-Draft PIM Group-to-RP Mapping February 2008 1. Introduction Multiple mechanisms exist today to create and distribute Group-to-RP mappings. Each PIM-SM router may learn Group-to-RP mappings through various mechanisms. It is critical that each router select the same 'RP' for a specific multicast group address. This is even true in the case of Anycast RP for redundancy. Routers should select the same RP address to use for a given group address. This RP address may correspond to a different physical router but it is one logical RP address and must be consistent across the PIM domain. This is usually achieved by using the same algorithm to select the RP in all the PIM routers in a domain. PIM-SM[1] has defined an algorithm to select a 'RP' for a given multicast group address but it is not flexible enough for an administrator to apply various policies. Please refer to section 3 for more details. PIM-STD-MIB [2] has defined an algorithm that allows administrators to override Group-to-RP mappings with static configuration. But this algorithm is not completely deterministic, because it includes an implementation-specific 'precedence' value. Joshi, et al. Expires August 16, 2008 [Page 3] Internet-Draft PIM Group-to-RP Mapping February 2008 2. Terminology In this document, the key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" are to be interpreted as described in RFC 2119 [1] and indicate requirement levels for compliant PIM-PING implementations. This document also uses following terms: o PIM Mode PIM Mode is the mode of operation a particular multicast group is used for. Wherever this term in used in this document, it refers to either Sparse Mode or BIDIR Mode. Joshi, et al. Expires August 16, 2008 [Page 4] Internet-Draft PIM Group-to-RP Mapping February 2008 3. Existing algorithm Existing algorithm defined in PIM-SM (Section 4.7.1 in [1]) does not consider following constraints: o It does not consider the origin of a Group-to-RP mapping and therefore will treat all of them equally. o It does not provide the flexibility that a specific statically created Group-to-RP mapping can override any dynamically learned mappings. o It does not provide the flexibility to give higher priority to a specific PIM mode. For example, an entry learned for PIM-BIDIR mode is treated with same priority as an entry learned for PIM-SM. Joshi, et al. Expires August 16, 2008 [Page 5] Internet-Draft PIM Group-to-RP Mapping February 2008 4. Assumptions We have made following assumptions in defining this algorithm: o A router MAY use hash function on Group-to-RP mappings learned through BSR mechanism [3]. This means that only a subset of Group-to-RP mappings will be available which are learned through BSR mechanism. o A static Group-to-RP mapping entry can be configured with override-dynamic flag. If this flag is set, the static Group-to-RP mapping entry will be preferred instead of dynamically learned entries. o A Group-to-RP mapping can be learned from various mechanisms. We assume that following list is in the decreasing preferences of these mechanism: * Bootstrap Router Mechanism [PIM-BSR] * Auto-RP [Cisco] * Embedded Group-to-RP mappings * Static configuration. * Other mapping method o A Group-to-RP mapping learned for PIM-BIDIR mode is preferred to an entry learned for PIM-SM mode. Joshi, et al. Expires August 16, 2008 [Page 6] Internet-Draft PIM Group-to-RP Mapping February 2008 5. Proposed algorithm We propose following algorithm here which addresses the above mentioned short comings in the existing mechanism: 1. From the set of all Group-to-RP mapping entries, the subset whose group prefix contains the multicast group that is being looked up, are selected. 2. If there are no entries available, then the Group-to-RP mapping is undefined. 3. If there are multiple entries available, a subset of those Group- to-RP mapping is selected that are learned using 'static' configuration and are configured with 'override-dynamic' flag. * If there is only one entry available then that is selected as Group-to-RP mapping. * If there are multiple entries available, we continue with the algorithm with this smaller set of Group-to-RP Mappings 4. A longest prefix match is performed on the subset of Group-to-RP Mappings. * If there is only one entry available then that is selected as Group-to-RP mapping. * If there are multiple entries available, we continue with the algorithm with this smaller set of Group-to-RP Mappings 5. From the remaining set of Group-to-RP Mappings we select the subset of entries based on the preference for the PIM modes which they are assigned. A Group-to-RP mapping entry with PIM Mode 'BIDIR' will be preferred to an entry with PIM Mode 'PIM-SM' * If there is only one entry available then that is selected as Group-to-RP mapping. * If there are multiple entries available, we continue with the algorithm with this smaller set of Group-to-RP Mappings 6. From the remaining set of Group-to-RP Mappings we select the subset of the entries based on the origin. Origin preference will be 'bsr', 'auto-rp', 'embedded', 'static' and 'other'. * If there is only one entry available then that is selected as Group-to-RP mapping. Joshi, et al. Expires August 16, 2008 [Page 7] Internet-Draft PIM Group-to-RP Mapping February 2008 * If there are multiple entries available, we continue with the algorithm with this smaller set of Group-to-RP Mappings 7. From the remaining set of Group-to-RP Mappings we run PIM hash function as suggested by PIM-SM [1]. * If there is only one entry available then that is selected as Group-to-RP mapping. * If there are multiple entries available, we continue with the algorithm with this smaller set of Group-to-RP Mappings 8. From the remaining set of Group-to-RP Mappings we will select the RP with the highest IP address. This will serve as a final tiebreaker. Joshi, et al. Expires August 16, 2008 [Page 8] Internet-Draft PIM Group-to-RP Mapping February 2008 6. Deprecation of MIB Objects Group-to-RP mapping algorithm defined in PIM-STD-MIB [2] does not specify the usage of 'pimGroupMappingPrecedence' and 'pimStaticRPPrecedence' objects in 'pimGroupMappingTable' table clearly. With the newly proposed algorithm in this document, these MIB objects would not be required. So we propose to deprecate these MIB objects from PIM-STD-MIB. Joshi, et al. Expires August 16, 2008 [Page 9] Internet-Draft PIM Group-to-RP Mapping February 2008 7. Security Consideration This document does not suggest any protocol specific functionality so there is no security related consideration. Joshi, et al. Expires August 16, 2008 [Page 10] Internet-Draft PIM Group-to-RP Mapping February 2008 8. IANA Consideration This draft does not create any namespace for IANA to manage. Joshi, et al. Expires August 16, 2008 [Page 11] Internet-Draft PIM Group-to-RP Mapping February 2008 9. Acknowledgments This draft is created based on the discussion occurred during the PIM-STD-MIB [2] work. Many thanks to Stig Vennas for providing useful comments during that discussion. 10. Normative References [1] Fenner, B., Handley, M., Holbrook, H., and I. Kouvelas, "Protocol Independent Multicast - Sparse Mode (PIM-SM): Protocol Specification (Revised)", RFC 4601, August 2006. [2] Sivaramu, R., Lingard, J., McWalter, D., Joshi, B., and A. Kessler, "Protocol Independent Multicast MIB", RFC 5060, January 2008. [3] Bhaskar, N., Gall, A., Lingard, J., and S. Venaas, "Bootstrap Router (BSR) Mechanism for Protocol Independent Multicast (PIM)", RFC 5059, January 2008. Joshi, et al. Expires August 16, 2008 [Page 12] Internet-Draft PIM Group-to-RP Mapping February 2008 Authors' Addresses Bharat Joshi Infosys Technologies Ltd. 44 Electronics City, Hosur Road Bangalore 560 100 India Email: bharat_joshi@infosys.com URI: http://www.infosys.com/ Andy Kessler Cisco Systems, Inc. 425 E. Tasman Drive San Jose, CA 95134 USA Email: kessler@cisco.com URI: http://www.cisco.com/ David McWalter Data Connection Ltd 100 Church Street Enfield EN2 6BQ UK Email: dmcw@dataconnection.com Joshi, et al. Expires August 16, 2008 [Page 13] Internet-Draft PIM Group-to-RP Mapping February 2008 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. 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Acknowledgment Funding for the RFC Editor function is currently provided by the Internet Society. Joshi, et al. Expires August 16, 2008 [Page 14]