PIM WG IJ. Wijnands Internet-Draft A. Boers Expires: August 5, 2005 E. Rosen Cisco Systems, Inc. february 2005 The RPF Vector Proxy draft-ietf-pim-rpf-vector-00 Status of this Memo This document is an Internet-Draft and is subject to all provisions of Section 3 of RFC 3667. 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 become aware will be disclosed, in accordance with RFC 3668. 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 5, 2005. Copyright Notice Copyright (C) The Internet Society (2005). Abstract This document describes a use of the PIM Proxy as defined in draft-pim-proxy [Forthcoming] which enables PIM to build multicast trees through an MPLS-enabled network, even if that network's IGP does not have a route to the source of the tree. Wijnands, et al. Expires August 5, 2005 [Page 1]
Internet-Draft The RPF Vector Proxy february 2005 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Use of the RPF Vector TLV . . . . . . . . . . . . . . . . . . 4 2.1 Proxy and shared tree joins . . . . . . . . . . . . . . . 4 2.2 The Vector Proxy . . . . . . . . . . . . . . . . . . . . . 4 2.2.1 Inserting a Vector Proxy in a Join . . . . . . . . . . 5 2.2.2 Processing a Received Vector Proxy . . . . . . . . . . 5 2.2.3 Vector Proxy and Asserts . . . . . . . . . . . . . . . 5 3. Vector Proxy TLV Format . . . . . . . . . . . . . . . . . . . 6 4. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 6 5. References . . . . . . . . . . . . . . . . . . . . . . . . . . 6 5.1 Normative References . . . . . . . . . . . . . . . . . . . 6 5.2 Informative References . . . . . . . . . . . . . . . . . . 7 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 7 Intellectual Property and Copyright Statements . . . . . . . . 8 Wijnands, et al. Expires August 5, 2005 [Page 2]
Internet-Draft The RPF Vector Proxy february 2005 1. Introduction It is sometimes convenient to distinguish the routers of a particular network into two categories: "edge routers" and "core routers". The edge routers attach directly to users or to other networks, but the core routers attach only to other routers of the same network. If the network is MPLS-enabled, then any unicast packet which needs to travel outside the network can be "tunneled" via MPLS from one edge router to another. To handle a unicast packet which must travel outside the network, an edge router needs to know which of the other edge routers is the best exit point from the network for that packet's destination IP address. The core routers, however, do not need to have any knowledge of routes which lead outside the network; as they handle only tunneled packets, they only need to know how to reach the edge routers and the other core routers. Consider, for example, the case where the network is an Autonomous System (AS), the edge routers are EBGP speakers, the core routers may be said to constitute a "BGP-free core". The edge routers must distribute BGP routes to each other, but not to the core routers. However, when multicast packets are considered, the strategy of keeping the core routers free of "external" routes is more problematic. When using PIM [I-D.ietf-pim-sm-v2-new] to create a multicast distribution tree for a particular multicast group, one wants the core routers to be full participants in the PIM protocol, so that multicasting can be done efficiently in the core.This means that the core routers must be able to correctly process PIM Join messages for the group, which in turn means that the core routes must be able to send the Join messages towards the root of the distribution tree. If the root of the tree lies outside the network's borders (e.g., is in a different AS), and the core routers do not maintain routes to external destinations, then the PIM Join messages cannot be processed, and the multicast distribution tree cannot be created. In order to allow PIM to work properly in an environment where the core routers do not maintain external routes, a PIM extension is needed. When an edge router sends a PIM Join message into the core, it must include in that message a "Vector" which specifies the IP address of the next edge router along the path to the root of the multicast distribution tree. The core routers can then process the Join message by sending it towards the specified edge router (i.e., toward the Vector). In effect, the Vector serves as a proxy, within a particular network, for the root of the tree. This document defines a new TLV in the PIM Proxy message[draft-pim-proxy]. It consists of a single Vector which Wijnands, et al. Expires August 5, 2005 [Page 3]
Internet-Draft The RPF Vector Proxy february 2005 identifies the exit point of the network. 2. Use of the RPF Vector TLV Before we can start forwarding multicast packets we need to build a forwarding tree by sending PIM Joins hop by hop. Each router in the path creates a forwarding state and propagates the Join towards the root of the forwarding tree. The building of this tree is receiver driven. See Figure 1. ------------------ BGP ----------------- | | [S]---( Edge 1)--(Core 1)---( Core )--(Core 2)---( Edge 2 )---[R] <--- (S,G) Join Figure 1 In this example, the 2 edge routers are BGP speakers. The core routers are not BGP speakers and do not have any BGP distributed routes. The route to S is a BGP distributed route, hence is known to the edge but not to the core. The Edge 2 router determines the interface leading to S, and sends a PIM Join to the upstream router. In this example, though, the upstream router is a core router, with no route to S. Without the PIM extensions specified in this document, the core router cannot determine where the send the Join, so the tree cannot be constructed. To allow the core router to participate in the construction of the tree, the Edge 2 router will include a Proxy field in the PIM Join. In this example, the Proxy field will contain the IP address of Edge 1. Edge 2 then forwards the PIM Join towards Edge 1. The intermediate core router do their RPF check on the Proxy (IP address of Edge 1) rather than the Source, this allows the tree to be constructed. 2.1 Proxy and shared tree joins In the example above we build a source tree to illustrate the proxy behavior. The proxy is however not restricted to source tree only. The tree may also be constructed towards a Rendezvous Point (RP) IP address. The RP IP address is used in a similar way as the Source in the example above. PIM Proxy procedures defined for sources are equally applicable to RPs unless otherwise noted. 2.2 The Vector Proxy Wijnands, et al. Expires August 5, 2005 [Page 4]
Internet-Draft The RPF Vector Proxy february 2005 2.2.1 Inserting a Vector Proxy in a Join In the example of Figure 1, when the Edge 2 router looks up the route to the source of the multicast distribution tree, it will find a BGP-distributed route whose "BGP next-hop" is Edge 1. Edge 2 then looks up the route to Edge 1 to find interface and PIM adjacency which is the next hop to the source, namely Core 2. When Edge 2 sends a PIM Join to Core 2, it includes a Vector Proxy specifying the address of Edge 1. Core 2, and subsequent core routers, will forwarding the Join along the Vector (i.e, towards Edge 1) instead of trying to forward it towards S. Whether a Proxy is actually needed depends on whether the Core routers have a route to the source of the multicast tree. How the Edge router knows whether or not this is the case (and thus how the Edge router determines whether or not to insert a Proxy field) is outside the scope of this document. 2.2.2 Processing a Received Vector Proxy When processing a received PIM Join which contains a Vector Proxy, a router must first check to see if the Vector IP address is one of its own IP addresses. If so, the Vector Proxy is discarded, and not passed further upstream. Otherwise, the Vector Proxy is used to find the route to the source, and is passed along when a PIM Join is sent upstream. Note that a router which receives a Vector Proxy must use it, even if that router happens to have a route to the source. A router which discards a Vector Proxy may of course insert a new Vector Proxy. This would typically happen if a PIM Join needed to pass through a sequence of Edge routers, each pair of which is separated by a core which does not have external routes. In the absence of periodic refreshment, Vectors expire along with the corresponding (S,G) state. 2.2.3 Vector Proxy and Asserts In a PIM Assert message we include the routing protocol's "metric" to the source of the tree. This information is used in the selection of the assert winner. If a PIM Join is being sent towards a Vector, rather than towards the source, the Assert message must have the metric to the Vector instead of the metric to the source. The Assert message however does not have a Proxy field and does not mention the Vector. A router may change its upstream neighbor on a particular multicast tree as the result of receiving Assert messages. However a Vector Proxy should not be sent in a PIM Join to an upstream neighbor which Wijnands, et al. Expires August 5, 2005 [Page 5]
Internet-Draft The RPF Vector Proxy february 2005 is chosen as the result of processing the Assert messages. Reachability of the Vector is only guaranteed by the router that advertises reachability to the Vector in it's IGP. If the assert winner upstream is not our real preferred next-hop, we can't be sure this router knows the path to the Vector. 3. Vector Proxy TLV Format 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |F| Type | Length | IP address +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-....... F bit ----- Forward Unknown TLV. If this bit is set the TLV is forwarded regardless if the router understands the Type. Type ---- The Vector Proxy type is 0. Length ------ Length in bytes is 4. Value ----- IPv4 address. 4. Acknowledgments The authors would like to thank Yakov Rekhter and Dino Farinacci for their initial ideas on this topic. 5. References 5.1 Normative References [I-D.ietf-pim-sm-v2-new] Fenner, B., Handley, M., Holbrook, H. and I. Kouvelas, "Protocol Independent Multicast - Sparse Mode PIM-SM): Protocol Specification (Revised)", Internet-Draft draft-ietf-pim-sm-v2-new-11, October 2004. Wijnands, et al. Expires August 5, 2005 [Page 6]
Internet-Draft The RPF Vector Proxy february 2005 5.2 Informative References Authors' Addresses IJsbrand Wijnands Cisco Systems, Inc. De kleetlaan 6a Diegem 1831 Belgium Email: ice@cisco.com Arjen Boers Cisco Systems, Inc. Avda. Diagonal, 682 Barcelona 08034 Spain Email: aboers@cisco.com Eric Rosen Cisco Systems, Inc. 1414 Massachusetts Avenue Boxborough, Ma 01719 Email: erosen@cisco.com Wijnands, et al. Expires August 5, 2005 [Page 7]
Internet-Draft The RPF Vector Proxy february 2005 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 ietf-ipr@ietf.org. Disclaimer of Validity 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. Copyright Statement Copyright (C) The Internet Society (2005). 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. Wijnands, et al. Expires August 5, 2005 [Page 8]