Network Working Group Yiqun Cai Internet Draft Eric C. Rosen (Editor) Intended Status: Proposed Standard IJsbrand Wijnands Expires: August 1, 2010 Cisco Systems, Inc. Maria Napierala AT&T Arjen Boers February 1, 2010 MVPN: Optimized use of PIM via MS-PMSIs draft-rosen-l3vpn-mvpn-mspmsi-06.txt Status of this Memo This Internet-Draft is submitted to IETF in full conformance with the 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. 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Abstract This document specifies an optimized method that a service provider can use to provide MVPN service when using PIM as the MVPN control protocol. As in prior MVPN methods, PIM control messages are sent over multicast tunnels through the provider network. However, unlike older MVPN methods, the tunnels are only created if they are needed to carry multicast data traffic; no tunnels are used only for control traffic. Table of Contents 1 Specification of requirements ......................... 3 2 Introduction .......................................... 3 2.1 Terminology ........................................... 3 3 MS-PMSI: Multidirectional Selective PMSI .............. 3 3.1 A PE's Primary MS-PMSI ................................ 4 3.2 Instantiating MS-PMSIs ................................ 5 3.2.1 Bidirectional P-Tunnels ............................... 5 3.2.2 Unidirectional P-Tunnels .............................. 5 3.2.2.1 PPMP LSPs ............................................. 5 3.2.2.2 Sparse Mode Groups .................................... 7 4 PIM over MS-PMSI ...................................... 7 5 IANA Considerations ................................... 8 6 Security Considerations ............................... 9 7 Acknowledgments ....................................... 9 8 Authors' Addresses .................................... 9 9 Normative References .................................. 10 10 Informative References ................................ 10 Rosen, et al. [Page 2] Internet Draft draft-rosen-l3vpn-mvpn-mspmsi-06.txt February 2010 1. Specification of requirements 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 [RFC2119]. 2. Introduction [MVPN] specifies how to run PIM [PIM] as the multicast routing protocol of a particular MVPN, by running it over an MI-PMSI for that MVPN. In this specification, we provide a specification for running PIM over an MS-PMSI. When PIM is run over an MI-PMSI, there may need to be P-tunnels that only carry PIM messages, but do not carry multicast data. However, when PIM is run over an MS-PMSI, there is never any need to create a P-tunnel just for control messages; the only P-tunnels needed are those that carry multicast data. 2.1. Terminology In the following, we will sometimes talk of a PE receiving traffic from a PMSI and then discarding it. If PIM is being used as the multicast control protocol between PEs, this always implies that the discarded traffic will not be seen by PIM on the receiving PE. In the following, we will sometimes speak of an S-PMSI A-D route being "ignored". When we say the route is "ignored", we do not mean that it's normal BGP processing is not done, but that the route is not considered when determining which P-tunnel to use when sending multicast data, and that the MPLS label values it conveys are not used. We will generally use "ignore" in quotes to indicate this meaning. 3. MS-PMSI: Multidirectional Selective PMSI [MVPN] defines three kinds of PMSI: - "Multidirectional Inclusive" PMSI (MI-PMSI) A Multidirectional Inclusive PMSI is one that enables ANY PE attaching to a particular MVPN to transmit a message such that it will be received by EVERY other PE attaching to that MVPN. Rosen, et al. [Page 3] Internet Draft draft-rosen-l3vpn-mvpn-mspmsi-06.txt February 2010 - "Unidirectional Inclusive" PMSI (UI-PMSI) A Unidirectional Inclusive PMSI is one that enables a particular PE, attached to a particular MVPN, to transmit a message such that it will be received by all the other PEs attaching to that MVPN. There is at most one UI-PMSI per PE per MVPN, though the P-tunnel that instantiates a UI-PMSI may in fact carry the data of more than one PMSI. - "Selective" PMSI (S-PMSI). A Selective PMSI is one that provides a mechanism wherein a particular PE in an MVPN can multicast messages so that they will be received by a subset of the other PEs of that MVPN. There may be an arbitrary number of S-PMSIs per PE per MVPN. In this document we add the notion of a "Multidirectional Selective PMSI" (MS-PMSI). An MS-PMSI provides a mechanism that enables a subset of PEs in a given MVPN to multicast messages so that they will be received by the other PEs that are in the subset. There may be an arbitrary number of MS-PMSIs per PE per MVPN. According to the definition of S-PMSI in [MVPN], only a single PE can transmit onto a given S-PMSI. An MS-PMSI may be thought of as a collection of S-PMSIs, each of which has the same subset of PEs as receivers. Although each S-PMSI in the set has a single PE as transmitter, the collection of S-PMSIs has all members of the subset as transmitters, and all members of the subset as receivers. 3.1. A PE's Primary MS-PMSI Although a PE may belong to many MS-PMSIs, we allow one MS-PMSI per PE to be distinguished as the MS-PMSI that is that PE's "primary MS- PMSI". A PE is considered to be advertising its primary MS-PMSI in a BGP S-PMSI A-D route if that route has the following properties: - the double wild card selector (C-*,C-*) [MVPN_WILD] is specified - the advertised S-PMSI is instantiated using one of the set of techniques described in the next section. Rosen, et al. [Page 4] Internet Draft draft-rosen-l3vpn-mvpn-mspmsi-06.txt February 2010 3.2. Instantiating MS-PMSIs There are a number of ways to instantiate MS-PMSIs. These are specified in in the follow sub-sections. Additional methods of instantiation may be added in the future. 3.2.1. Bidirectional P-Tunnels An MS-PMSI be instantiated as a bidirectional P-tunnel. See [MVPN_BIDIR] for the details of advertising bidirectional P-tunnels. [MVPN_BIDIR] specifies two kinds of bidirectional P-tunnels (P- tunnels that are BIDIR-PIM[BIDIR-PIM] multicast trees, or that are MP2MP LSPs [MLDP] without PE distinguisher labels) that may only be advertised by their "roots" (as defined in that document). It follows that a PE may advertise such a P-tunnel as the instantiation of its primary MS-PMSI only if that PE is the root of the P-tunnel. If PE1, PE2, ..., PEn are using a MP2MP LSP with PE Distinguisher labels to instantiate an MS-PMSI, the MP2MP LSP should be thought of as instantiating n MS-PMSIs, each one being the primary MS-PMSI of one of the PEs. A packet traveling on the MP2MP LSP is said to be traveling PEi's primary MS-PMSI if it is carrying the PE Distinguisher label that the root of the LSP has assigned to PEi. 3.2.2. Unidirectional P-Tunnels The use of MS-PMSIs instantiated as unidirectional P-tunnels is NOT recommended for carrying bidirectional C-flows. It can however be useful for carrying unidirectional C-flows. 3.2.2.1. PPMP LSPs An MS-PMSI can be implemented as a Point-to-Point-to-Multipoint (PPMP) LSP. (See, e.g, the "shared P2MP LSP" of [mLDP] section 3.) The procedures for advertising a PPMP LSP in an S-PMSI A-D route are as follows. A new BGP attribute is defined, the "PPMP Label" attribute. This is an optional transitive attribute defined as follows: Rosen, et al. [Page 5] Internet Draft draft-rosen-l3vpn-mvpn-mspmsi-06.txt February 2010 +---------------------------------+ | MPLS Label (3 octets) | +---------------------------------+ This attribute may be carried by a BGP S-PMSI A-D route that is advertising a primary MS-PMSI instantiated as a P2MP LSP. The PPMP label is a downstream-assigned MPLS label assigned by the PE that originated the route carrying this attribute. A PPMP label MUST NOT be added to an S-PMSI A-D route UNLESS the route contains a PTA identifying a P2MP LSP, and the route is origi- nated by the root of the LSP. The rules for transmitting packets on a PPMP LSP are as follows: - The root of the LSP transmits normally, without using the PPMP label. - A PE which is not the root of the LSP transmits a packet on the LSP as follows: * it pushes the PPMP label onto the packet's label stack, then * it unicasts the packet to the PE that is the root of the LSP; this requires pushing another label onto the packet's label stack. When the packet is received (as a unicast) by the PE at root of the LSP, the PPMP label will either be at the top of the label stack (if penultimate hop popping is in use), or else will rise to the . The PPMP label is then popped from the stack, and that PE processes packet's label stack, recognizes the PPMP label, and as a result retransmits the packet on the corresponding P2MP LSP. In addition, the PE at the root of the P2MP processes the received packet as a multicast packet in the context of the VPN corresponding to the PPMP label. (The relationship between a PPMP label and a VPN is established by the RTs carried by the S-PMSI A-D route that advertised the PPMP label.) Note that when an MS-PMSI is instantiated as a PPMP LSP, the PE that transmits a given packet may receive it back. A PE MUST discard, without processing, any packet it receives from the PPMP LSP if it transmitted that packet to the PPMP LSP. As a result, the procedure of instantiating an MS-PMSI as a PPMP LSP MUST NOT be used UNLESS there is a method by which a PE can identify the packets it transmitted. It is recommended to use this method only for transmitting PIM control packets, rather than multicast data packets. Rosen, et al. [Page 6] Internet Draft draft-rosen-l3vpn-mvpn-mspmsi-06.txt February 2010 3.2.2.2. Sparse Mode Groups One way to instantiate an MS-PMSI is to use a PIM sparse mode group. Each PE can advertises its primary MS-PMSI by sending an S-PMSI A-D route whose PTA identifies a "PIM-SM Tree". Every PE would have to advertise a PIM-SM tree with a distinct group address. Generally speaking, this is not an efficient method of instantiating an MS-PMSI. However, it can be useful in certain circumstances, such as the "hub and spoke" MVPN discussed in [MVPN_EXTRANET]. 4. PIM over MS-PMSI [MVPN] provides two alternative means of distributing C-multicast routing information: PIM or BGP. Procedures for running PIM over MI-PMSI are specified in that document. However, a number of efficiencies can be obtained by running PIM instead over MS-PMSI. The procedures for this are as follows. Each PE that attaches to a given MVPN MUST originate an Intra-AS I-PMSI A-D route that does NOT contain a PTA. Each such PE MUST also advertise a primary MS-PMSI instantiated by one of the methods described in the previous section. By default, each a PE needing to send data traffic to other PEs sends the traffic on its primary MS-PMSI. If PE1 needs to direct a PIM Join/Prune message to PE2, PE1 MUST join the PE2's primary MS-PMSI by joining the P-tunnel advertised in PE2's corresponding S-PMSI A-D route. The PIM J/P messages MUST be sent over that MS-PMSI. If PE1 does not need to direct a PIM Join/Prune message to PE2, then PE1 SHOULD NOT join the P-tunnel advertised in PE2's S-PMSI A-D route, as PE1 will not be receiving any multicast data on that LSP. Any PE that sends a PIM Join/Prune message on a given P-tunnel is automatically considered to be a PIM adjacency of every PE that receives the message on that P-tunnel. This implies that any PE receiving the LSP MUST accept a PIM Join/Prune message on that P-tunnel from any other PE, even if the PE that transmitted the Join/Prune messages has not previously transmitted a PIM Hello. That is, the "adjacency relationship" does not depend on the reception of PIM Hellos. PIM Hellos may still be useful for OAM purposes. Any PIM Hellos that PE1 sends MUST be sent on the P-tunnel advertised in PE1's S-PMSI A-D Rosen, et al. [Page 7] Internet Draft draft-rosen-l3vpn-mvpn-mspmsi-06.txt February 2010 route above. Standard PIM procedures are used, except for: - The above change in the adjacency maintenance procedures. - Changes in the "RPF determination" or "RPF checking" procedures as may be defined in [MVPN] or in subsequent sections of this document (such as section 8.2). If an MS-PMSI is instantiated as a bidirectional P-tunnel, then the data handling procedures of [MVPN_BIDIR] will prevent PIM from ever seeing any packets that come from the wrong transmitter or that are in the wrong partition; when such packets are received they are discarded, rather than being passed to PIM's state machinery. As a result, such packets do not cause Asserts to be generated. Other standard PIM procedures, such as Join Suppression and Prune Override may come into play, however. If an MS-PMSI is instantiated as a PPMP tree, a PE that transmits a Join/Prune message will receive it back. Any such message is easily identified by its source address, and MUST be discarded. A PE only transmits data packets on its primary MS-PMSI, and hence does not receive them back. By running PIM over MS-PMSI instead of over MI-PMSI, one completely avoids the need to have PEs join P-tunnels that would carry only control messages. A PE need not ever join a particular a P-tunnel unless it either has data to send on it, or needs to receive data on it. All other MVPN-specific PIM procedures are as specified in [MVPN]. 5. IANA Considerations This document specifies a new BGP optional transitive attribute, "PPMP Label". A value must be assigned from the "BGP Path Attributes Registry". Rosen, et al. [Page 8] Internet Draft draft-rosen-l3vpn-mvpn-mspmsi-06.txt February 2010 6. Security Considerations There are no additional security considerations beyond those of [MVPN] and [MVPN-BGP]. 7. Acknowledgments The "PPMP" mechanism is similar to a mechanism that appeared in earlier drafts of [MVPN], known as "unicasting to the root of a shared tree"; this mechanism was discussed among the authors of [MVPN]. The possibility of using of sparse mode groups to instantiate MS- PMSIs arose from a discussion with Yakov Rekhter. 8. Authors' Addresses Arjen Boers E-mail: arjen@boers.com Yiqun Cai Cisco Systems, Inc. 170 Tasman Drive San Jose, CA, 95134 E-mail: ycai@cisco.com Maria Napierala AT&T Labs 200 Laurel Avenue, Middletown, NJ 07748 E-mail: mnapierala@att.com Eric C. Rosen Cisco Systems, Inc. 1414 Massachusetts Avenue Boxborough, MA, 01719 E-mail: erosen@cisco.com Rosen, et al. [Page 9] Internet Draft draft-rosen-l3vpn-mvpn-mspmsi-06.txt February 2010 IJsbrand Wijnands Cisco Systems, Inc. De kleetlaan 6a Diegem 1831 Belgium E-mail: ice@cisco.com 9. Normative References [BIDIR-PIM] "Bidirectional Protocol Independent Multicast", Handley, Kouvelas, Speakman, Vicisano, RFC 5015, October 2007 [MLDP] "Label Distribution Protocol Extensions for Point-to-Multipoint and Multipoint-to-Multipoint Label Switched Paths", Minei, Kompella, Wijnands, Thomas, draft-ietf-mpls-ldp-p2mp-08.txt, October 2009 [MVPN] "Multicast in MPLS/BGP IP VPNs", Rosen, Aggarwal, et. al., draft-ietf-l3vpn-2547bis-mcast-10.txt, January 2010 [MVPN-BGP] "BGP Encodings and Procedures for Multicast in MPLS/BGP IP VPNs", Aggarwal, Rosen, Morin, Rekhter, draft-ietf-l3vpn-2547bis-mcast-bgp-08.txt, October 2009 [MVPN_BIDIR] "MVPN: Using Bidirectional P-Tunnels", Cai, Rosen, Wijnands, Boers, draft-rosen-l3vpn-mvpn-bidir-00.txt, February 2010 [MVPN_WILD] "MVPN: S-PMSI Wild Card Selectors", Cai, Rosen, Wijnands, draft-rosen-l3vpn-mvpn-wildcards-00.txt, February 2010 [PIM] "Protocol Independent Multicast - Sparse Mode (PIM-SM): Protocol Specification (Revised)", Fenner, Handley, Holbrook, Kouvelas, RFC 4601, August 2006 [RFC2119] "Key words for use in RFCs to Indicate Requirement Levels.", Bradner, March 1997 10. Informative References [MVPN_EXTRANET] "MVPN: Extranets, Anycast-Sources, 'Hub & Spoke', with PIM Control Plane", Cai, Rosen, Sharma, Wijnands, draft-rosen- l3vpn-mvpn-extranet-00.txt, January 2010 Rosen, et al. [Page 10]