PIM Working Group B. Joshi Internet-Draft Infosys Technologies Ltd. Expires:
April 24,December 27, 2009 A. Kessler Cisco Systems, Inc. D. McWalter Data Connection Ltd October 21, 2008June 25, 2009 PIM Group-to-RP Mapping draft-ietf-pim-group-rp-mapping-00.txtdraft-ietf-pim-group-rp-mapping-01.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 sheThis Internet-Draft is aware have been or will be disclosed, and any of which he or she becomes aware will be disclosed,submitted to IETF in accordancefull conformance with Section 6the provisions of BCP 78 and 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 April 24,December 27, 2009. Copyright Notice Copyright (c) 2009 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents in effect on the date of publication of this document (http://trustee.ietf.org/license-info). Please review these documents carefully, as they describe your rights and restrictions with respect to this document. 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- 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. The intention of this document is to suggest a standard algorithm to deterministically choose between several group-to-rp mappings for a specific group. 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 . . . . . . . . . . . . . . . . . . . . . . . . . 4 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5 3. Existing algorithm . . . . . . . . . . . . . . . . . . . . . . 6 4. Assumptions . . . . . . . . . . . . . . . . . . . . . . . . . 7 5. Common use cases . . . . . . . . . . . . . . . . . . . . . . . 8 6. Proposed algorithm . . . . . . . . . . . . . . . . . . . . . . 10 7. Deprecation of MIB Objects . . . . . . . . . . . . . . . . . . 12 8. Clarification for MIB Objects . . . . . . . . . . . . . . . . 13 9. Security Consideration . . . .Migration to the new algorithm . . . . . . . . . . . . . . . . 14 10. IANASecurity Consideration . . . . . . . . . . . . . . . . . . . . . .15 11. Acknowledgments .IANA Consideration . . . . . . . . . . . . . . . . . . . . . . 16 12. Normative ReferencesAcknowledgments . . . . . . . . . . . . . . . . . . . . . . . 17 Authors' Addresses13. Normative References . . . . . . . . . . . . . . . . . . . . . 18 Authors' Addresses . . . . . . . . . . . . . . 18 Intellectual Property and Copyright Statements. . . . . . . . . . 19 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[RFC4601] 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 [RFC5060] 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. Embedded-RP as defined in section-7.1 of Embedded-RP address in IPv6 Multicast address [RFC3956], mentions that to avoid loops and inconsistencies, for addresses in the range FF70::/12, the Embedded-RP mapping must be considered the longest possible match and higher priority than any other mechanism. 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. 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. 3. Existing algorithm Existing algorithm defined in PIM-SM (Section 4.7.1 in [RFC4601]) 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. 4. Assumptions We have made following assumptions in defining this algorithm: o PIM-SM [RFC4601] and BSR [RFC5059] suggested use of a hash function as the last step to select a RP from multiple Group-to-RP mappings. There seems to be no requirement for this function, so this draft assumes that the step to apply hash function can be removed. 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 Group-to-RP mappings created with the embedded RP extracted from Multicast Group addresses are special and always has the highest priority. These mappings can not be overridden by a static Group- to-RP mapping with override-dynamic flag set. 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: * Embedded Group-to-RP mappings * Bootstrap Router Mechanism [PIM-BSR] * Auto-RP [Cisco] * 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. 5. Common use cases o Default static Group-to-RP mappings with dynamically learned entries Many network operators will have a dedicated infrastructure for the standard multicast group range (224/4) and so might be using statically configured Group-to-RP mappings for this range. In this case, to support some specific applications, they might like to learn Group-to-RP mappings dynamically using either BSR or Auto-RP mechanism. In this case to select Group-to-RP mappings for these specific applications, a longer prefix match should be given preference over statically configured Group-to-RP mappings. For example 188.8.131.52/16 could be learned for a corporate communications application. Network operators may change the Group- to-RP mappings for these applications more often and would need to be learned dynamically. o Static Group-to-RP mappings with override-dynamic flag Many Network operators would like to statically configure one or multiple Group-to-RP mappings and would always want to ignore any dynamically learned mappings through either BSR, AutoRP or embedded RP for these group prefixes. This is accomplished by providing a 'override-dynamic' flag for Group-to-RP mapping configuration. When this flag is enabled for a static Group-to-RP mapping, it will have the highest precedence and would always be use for the specified group prefix. For example: 184.108.40.206/16 is configured with override- dynamic flag enabled and uses RP address RP1. If the router learns the more specific group prefix 220.127.116.11/24 which uses RP2 through BSR, it will choose the RP1 for any group falling under 18.104.22.168/16 range. o Migration situations Network operators occasionally go through a migration due to an acquisition or a change in their network design. In order to facilitate this migration there is a needs to have a deterministic behavior of Group-to-RP mapping selection for entries learned using BSR and AutoRP mechanism. This will help in avoiding any unforeseen interoperability issues between different vendor's network elements. o Use by management systems A network management system [or a stand alone box] can find out RP for a specific group in a specific router by running this algorithm on the Group-to-RP mapping table fetched using SNMP MIB objects. o More use cases By no means, the above list is complete. Please drop a mail to 'authors' if you see any other use case for this. 6. Proposed algorithm We propose following algorithm here which addresses the above mentioned shortcomings in the existing mechanism: 1. If the Multicast Group Address being looked up contains an embedded RP, RP address extracted from the Group address is selected as Group-to-RP mapping. 2. If the Multicast Group Address being looked up is in the SSM range or is configured for Dense mode, no Group-to-RP mapping is selected, and this algorithm terminates. Alternatively, a RP with address type 'unknown' can be selected. Please look at section #8 for more details on this. 3. 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. 4. If there are no entries available, then the Group-to-RP mapping is undefined. 5. 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 * If there are no static entries with 'override-dynamic' flag set then we continue with the original subset of Group-to-RP Mappings from step 2. 6. 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 7. 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 8. 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', 'static' and 'other'. * 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 9. 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. 7. Deprecation of MIB Objects Group-to-RP mapping algorithm defined in PIM-STD-MIB [RFC5060] 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. Also the newly proposed algorithm in this document MUST be preferred over Group-to-RP mapping algorithm defined in either PIM-SM[RFC4601] or in PIM-STD-MIB[RFC5060]. 8. Clarification for MIB Objects When an Group-to-RP mapping entry is created in the pimGroupMappingTable in the PIM-STD MIB[RFC5060], it would be acceptable to have an entry with an RP with address type 'unknown' and a PimMode of Dense Mode or SSM. These entries would represent group ranges for Dense mode or SSM. Also all the entries which are already included in the SSM Range table in the IP Mcast MIB would be copied over to pimGroupMappingTable. They would have a type of configSSM and an RP with address type 'unknown' as described above. The advantage of keeping all the ranges in the table would be that this table will contain all the known multicast group ranges. 9. Migration to the new algorithm The Group-to-RP mapping algorithm proposed in this document obsoletes the use of the hash function. With this change, there will be no interoperability between the old and the new algorithm. So networks that use multiple RP addresses for a Group Range and use the hash function for load sharing will need to be migrated to the new algorithm proposed in this document. A seamless migration to the new Group-to-RP algorithm can be accomplished by using one RP address with Anycast RP. 10. Security Consideration This document does not suggest any protocol specific functionality so there is no security related consideration. 10.11. IANA Consideration This draft does not create any namespace for IANA to manage. 11.12. Acknowledgments This draft is created based on the discussion occurred during the PIM-STD-MIB [RFC5060] work. Many thanks to Stig Vennas and Toerless Eckert for providing useful comments during that discussion. 12.13. 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. [RFC5060] Sivaramu, R., Lingard, J., McWalter, D., Joshi, B., and A. Kessler, "Protocol Independent Multicast MIB", RFC 5060, January 2008. [RFC3956] Savola, P. and B. Haberman, "Embedding the Rendezvous Point (RP) Address in an IPv6 Multicast Address", RFC 3956, November 2004. [RFC5059] Bhaskar, N., Gall, A., Lingard, J., and S. Venaas, "Bootstrap Router (BSR) Mechanism for Protocol Independent Multicast (PIM)", RFC 5059, January 2008. Authors' Addresses Bharat Joshi Infosys Technologies Ltd. 44 Electronics City, Hosur Road Bangalore 560 100 India Email: email@example.com URI: http://www.infosys.com/ Andy Kessler Cisco Systems, Inc. 425 E. Tasman Drive San Jose, CA 95134 USA Email: firstname.lastname@example.org URI: http://www.cisco.com/ David McWalter Data Connection Ltd 100 Church Street Enfield EN2 6BQ UK Email: email@example.com Full Copyright Statement Copyright (C) The IETF Trust (2008). 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. 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