INTERNET DRAFT Y. Serbest Internet Engineering Task Force SBC Document: Ray Qiu draft-serbest-l2vpn-vpls-mcast-01.txt Venu Hemige November 2004 Alcatel Category: Informational Rob Nath Expires: May 2005 Riverstone Supporting IP Multicast over VPLS Status of this memo By submitting this Internet-Draft, we represent that any applicable patent or other IPR claims of which we are aware have been disclosed, or will be disclosed, and any of which we become aware will be disclosed in accordance with RFC 3668. This document is an Internet-Draft and is in full conformance with Sections 5 and 6 of RFC 3667 and Section 5 of 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. Abstract In Virtual Private LAN Service (VPLS), the PE devices provide a logical interconnect such that CE devices belonging to a specific VPLS instance appear to be connected by a single LAN. A VPLS solution performs replication for multicast traffic at the ingress PE devices. When replicated at the ingress PE, multicast traffic wastes bandwidth when 1. Multicast traffic is sent to sites with no members, and 2. Pseudo wires to different sites go through a shared path. This document is addressing the former by IGMP and PIM snooping. Conventions used in this document [Page 1]
Internet Draft draft-serbest-l2vpn-vpls-mcast-01.txt November, 2004 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. Table of Contents 1 Contributing Authors..............................................3 2 Introduction......................................................3 3 Overview of VPLS..................................................4 4 Multicast Traffic over VPLS.......................................4 5 Constraining of IP Multicast in a VPLS............................5 5.1 General Rules for IGMP/PIM Snooping in VPLS....................6 5.2 IGMP Snooping for VPLS.........................................6 5.2.1 Discovering Multicast Routers...............................7 5.2.2 IGMP Join...................................................8 5.2.3 IGMP Leave.................................................12 5.2.4 Failure Scenarios..........................................13 5.3 PIM Snooping for VPLS.........................................13 5.3.1 PIM-DM.....................................................15 5.3.1.1 Discovering Multicast Routers............................15 5.3.1.2 PIM-DM Multicast Forwarding..............................16 5.3.1.3 PIM-DM Pruning...........................................16 5.3.1.4 PIM-DM Grafting..........................................17 5.3.1.5 Failure Scenarios........................................18 5.3.2 PIM-SM.....................................................18 5.3.2.1 Discovering Multicast Routers............................19 5.3.2.2 PIM-SM (*,G) Join........................................19 5.3.2.3 PIM-SM Pruning...........................................21 5.3.2.4 PIM-SM (S,G) Join........................................22 5.3.2.5 PIM-SM (*,*,RP) State....................................22 5.3.2.6 Failure Scenarios........................................23 5.3.2.7 Special Cases for PIM-SM Snooping........................23 5.3.3 PIM-SSM....................................................24 5.3.3.1 Discovering Multicast Routers............................25 5.3.3.2 Guidelines for PIM-SSM Snooping..........................25 5.3.3.3 PIM-SSM Join.............................................25 5.3.3.4 PIM-SSM Prune............................................26 5.3.3.5 Failure Scenarios........................................27 5.3.3.6 Special Cases for PIM-SSM Snooping.......................27 5.3.4 Bidirectional-PIM (BIDIR-PIM)..............................27 5.3.4.1 Discovering Multicast Routers............................27 5.3.4.2 Guidelines for BIDIR-PIM Snooping........................29 5.3.4.3 BIDIR-PIM Join...........................................29 5.3.4.4 BIDIR-PIM Prune..........................................30 5.3.4.5 Failure Scenarios........................................31 5.3.5 Multicast Source Directly Connected to the VPLS Instance...31 6 Security Considerations..........................................32 7 References.......................................................32 7.1 Normative References..........................................32 7.2 Informative References........................................32 8 Authors' Addresses...............................................32 9 Intellectual Property Statement..................................33 10 Full copyright statement......................................34 [Page 2]
Internet Draft draft-serbest-l2vpn-vpls-mcast-01.txt November, 2004 1 Contributing Authors This document was the combined effort of several individuals. The following are the authors, in alphabetical order, who contributed to this document: Suresh Boddapati Venu Hemige Sunil Khandekar Vach Kompella Marc Lasserre Rob Nath Ray Qiu Yetik Serbest 2 Introduction In Virtual Private LAN Service (VPLS), the Provider Edge (PE) devices provide a logical interconnect such that Customer Edge (CE) devices belonging to a specific VPLS instance appear to be connected by a single LAN. Forwarding information base for particular VPLS instance is populated dynamically by source MAC address learning. This is a straightforward solution to support unicast traffic, with reasonable flooding for unicast unknown traffic. Since a VPLS provides LAN emulation for IEEE bridges as wells as for routers, the unicast and multicast traffic need to follow the same path for layer-2 protocols to work properly. As such, multicast traffic is treated as broadcast traffic and is flooded to every site in the VPLS instance. VPLS solutions (i.e., [VPLS-LDP] and [VPLS-BGP]) perform replication for multicast traffic at the ingress PE devices. When replicated at the ingress PE, multicast traffic wastes bandwidth when: 1. Multicast traffic is sent to sites with no members, 2. Pseudo wires to different sites go through a shared path, and 3. Multicast traffic is forwarded along a shortest path tree as opposed to the minimum cost spanning tree. This document is addressing the first problem by IGMP and PIM snooping. Using VPLS in conjunction with IGMP and/or PIM snooping has the following advantages: - It improves VPLS to support IP multicast efficiently (not necessarily optimum, as there can still be bandwidth waste), - It prevents sending multicast traffic to sites with no members, - It keeps P routers in the core stateless, - The Service Provider (SP) does not need to perform the tasks to provide multicast service (e.g., running PIM, managing P-group addresses, managing multicast tunnels) - The SP does not need to maintain PIM adjacencies with the customers. In this document, we describe the procedures for Internet Group Management Protocol (IGMP) and Protocol Independent Multicast (PIM) [Page 3]
Internet Draft draft-serbest-l2vpn-vpls-mcast-01.txt November, 2004 snooping over VPLS for efficient distribution of IP multicast traffic. 3 Overview of VPLS In case of VPLS, the PE devices provide a logical interconnect such that CE devices belonging to a specific VPLS appear to be connected by a single LAN. End-to-end VPLS consists of a bridge module and a LAN emulation module ([L2VPN-FR]). In a VPLS, a customer site receives Layer-2 service from the SP. The PE is attached via an access connection to one or more CEs. The PE performs forwarding of user data packets based on information in the Layer-2 header, that is, MAC destination address. The CE sees a bridge. The details of VPLS reference model, which we summarize here, can be found in [L2VPN_FR]. In VPLS, the PE can be viewed as containing a Virtual Switching Instance (VSI) for each L2VPN that it serves. A CE device attaches, possibly through an access network, to a bridge module of a PE. Within the PE, the bridge module attaches, through an Emulated LAN Interface to an Emulated LAN. For each VPLS, there is an Emulated LAN instance. The Emulated LAN consists of VPLS Forwarder module (one per PE per VPLS service instance) connected by pseudo wires (PW), where the PWs may be traveling through Packet Switched Network (PSN) tunnels over a routed backbone. VSI is a logical entity that contains a VPLS forwarder module and part of the bridge module relevant to the VPLS service instance [L2VPN-FR]. Hence, the VSI terminates PWs for interconnection with other VSIs and also terminates attachment circuits (ACs) for accommodating CEs. A VSI includes the forwarding information base for a L2VPN [L2VPN- FR] which is the set of information regarding how to forward Layer-2 frames received over the AC from the CE to VSIs in other PEs supporting the same L2VPN service (and/or to other ACs), and contains information regarding how to forward Layer-2 frames received from PWs to ACs. Forwarding information bases can be populated dynamically (such as by source MAC address learning) or statically (e.g., by configuration). Each PE device is responsible for proper forwarding of the customer traffic to the appropriate destination(s) based on the forwarding information base of the corresponding VSI. 4 Multicast Traffic over VPLS In VPLS, if a PE receives a frame from an Attachment Circuit (AC) with no matching entry in the forwarding information base for that particular VPLS instance, it floods the frame to all other PEs (which are part of this VPLS instance) and to directly connected ACs (other than the one that the frame is received from). The flooding of a frame occurs when: - The destination MAC address has not been learned, - The destination MAC address is a broadcast address, - The destination MAC address is a multicast address. [Page 4]
Internet Draft draft-serbest-l2vpn-vpls-mcast-01.txt November, 2004 Malicious attacks (e.g., receiving unknown frames constantly) aside, the first situation is handled by VPLS solutions as long as destination MAC address can be learned. After that point on, the frames will not be flooded. A PE is REQUIRED to have safeguards, such as unknown unicast limiting and MAC table limiting, against malicious unknown unicast attacks. There is no way around flooding broadcast frames. To prevent runaway broadcast traffic from adversely affecting the VPLS service and the SP network, a PE is REQUIRED to have tools to rate limit the broadcast traffic as well. Similar to broadcast frames, multicast frames are flooded as well, as a PE can not know where multicast members reside. Rate limiting multicast traffic, while possible, should be should be done carefully since several network control protocols relies on multicast. For one thing, layer-2 and layer-3 protocols utilize multicast for their operation. For instance, Bridge Protocol Data Units (BPDUs) use an IEEE assigned all bridges multicast MAC address, and OSPF is multicast to all OSPF routers multicast MAC address. If the rate-limiting of multicast traffic is not done properly, the customer network will experience instability and poor performance. For the other, it is not straightforward to determine the right rate limiting parameters for multicast. A VPLS solution MUST NOT affect the operation of customer layer-2 protocols (e.g., BPDUs). Additionally, a VPLS solution MUST NOT affect the operation of layer-3 protocols. In the following section, we describe procedures to constrain the flooding of IP multicast traffic in a VPLS. 5 Constraining of IP Multicast in a VPLS The objective of improving the efficiency of VPLS for multicast traffic that we are trying to optimize here has the following constraints: - The service is VPLS, i.e., a layer-2 VPN, - In VPLS, ingress replication is required, - There is no layer-3 adjacency (e.g., PIM) between a CE and a PE. Under these circumstances, the most obvious approach is implementation of IGMP and PIM snooping in VPLS. Other multicast routing protocols such as DVMRP and MOSPF are outside the scope of this document. Another approach to constrain multicast traffic in a VPLS is to utilize point-multipoint LSPs (e.g., [PMP-RSVP-TE]). In such case, one has to establish a point-multipoint LSP from a source PE (i.e., the PE to which the source router is connected to) to all other PEs [Page 5]
Internet Draft draft-serbest-l2vpn-vpls-mcast-01.txt November, 2004 participating in the VPLS instance. In this case, if nothing is done, all PEs will receive multicast traffic even if they donÆt have any members hanging off of them. One can apply IGMP/PIM snooping, but this time IGMP/PIM snooping should be done in P routers as well. One can propose a dynamic way of establishing point-multipoint LSPs, for instance by mapping IGMP/PIM messages to RSVP-TE signaling. One should consider the effect of such approach on the signaling load and on the delay between the time the join request received and the traffic is received (this is important for IPTV application for instance). This approach is outside the scope of this document. Although, in some extremely controlled cases, such as a ring topology of PE routers with no P routers or a tree topology, the efficiency of the replication of IP multicast can be improved. For instance, spoke PWs of a hierarchical VPLS can be daisy-chained together and some replication rules can be devised. These cases are not expected to be common and will not be considered in this document. In the following sections, we provide some guidelines for the implementation of IGMP and PIM snooping in VPLS. 5.1 General Rules for IGMP/PIM Snooping in VPLS The following rules for the correct operation of IGMP/PIM snooping MUST be followed. Rule 1: IGMP and PIM messages forwarded by PEs MUST follow the split-horizon rule for mesh PWs as defined in [VPLS-LDP]. Rule 2: IGMP/PIM snooping states in a PE MUST be per VPLS instance. Rule 3: If a PE does not have any entry in a IGMP/PIM snooping state for multicast group (*,G) or (S,G), the multicast traffic to that group in the VPLS instance MUST be flooded. Rule 4: A PE MUST support PIM mode selection per VPLS instance via CLI and/or EMS. Another option could be to deduce the PIM mode from RP address for a specific multicast group. For instance, a RP address can be learned during the Designated Forwarder (DF) election stage for Bidirectional-PIM. 5.2 IGMP Snooping for VPLS IGMP is a mechanism to inform the routers on a subnet of a hostÆs request to become a member of a particular multicast group. IGMP is a stateful protocol. The router (i.e., the querier) regularly verifies that the hosts want to continue to participate in the multicast groups by sending periodic queries, transmitted to all hosts multicast group (IP:224.0.0.1, MAC:01-00-5E-00-00-01) on the subnet. If the hosts are still interested in that particular multicast group, they respond with membership report message, transmitted to the multicast group of which they are members. In IGMPv1 [RFC1112], the hosts simply stop responding to IGMP queries [Page 6]
Internet Draft draft-serbest-l2vpn-vpls-mcast-01.txt November, 2004 with membership reports, when they want to leave a multicast group. IGMPv2 [RFC2236] adds a leave message that a host will use when it needs to leave a particular multicast group. IGMPv3 [RFC3376] extends the report/leave mechanism beyond multicast group to permit joins and leaves to be issued for specific source/group (S,G) pairs. In IGMP snooping, a PE snoops on the IGMP protocol exchange between hosts and routers, and based on that restricts the flooding of IP multicast traffic. In the following, we explore the mechanisms involved in implementing IGMP snooping for VPLS. Please refer to Figure 1 as an example of VPLS with IGMP snooping. In the figure, Router 1 is the Querier. If multiple routers exist on a single subnet (basically that is what a VPLS instance is), they can mutually elect a designated router (DR) that will manage all of the IGMP messages for that subnet. VPLS Instance +------+ AC1 +------+ +------+ AC4 +------+ | Host |-----| PE |-------------| PE |-----|Router| | 1 | | 1 |\ PW1to3 /| 3 | | 1 | +------+ +------+ \ / +------+ +------+ | \ / | | \ / | | \ /PW2to3 | | \ / | PW1to2| \ |PW3to4 | / \ | | / \PW1to4 | | / \ | | / \ | +------+ +------+ / \ +------+ +------+ | Host | | PE |/ PW2to4 \| PE | |Router| | 2 |-----| 2 |-------------| 4 |-----| 2 | +------+ AC2 +------+ +------+ AC5 +------+ | |AC3 +------+ | Host | | 3 | +------+ Figure 1 Reference Diagram for IGMP Snooping for VPLS 5.2.1 Discovering Multicast Routers A PE need to discover the multicast routers in VPLS instances. This is necessary because: - Designated Router can be different from the Querier on a LAN. - It is not always the Querier that initiates PIM joins [Page 7]
Internet Draft draft-serbest-l2vpn-vpls-mcast-01.txt November, 2004 - Multicast traffic to the LAN could arrive from a non-querying router because it could be the closest to the source. As recommended in [MAGMA-SNOOP], the PEs can discover multicast routers using Multicast Router Discovery Protocol or they can be statically configured. Since multicast routing protocols other than PIM is out scope, multicast routers can also be discovered by snooping PIM Hello packets as described in Section 5.3.1. 5.2.2 IGMP Join The IGMP snooping mechanism for joining a multicast group (for all IGMP versions) works as follows: - The Querier sends a membership query to all hosts (IP:224.0.0.1, MAC:01-00-5E-00-00-01). The membership query can be either general query or group specific query. - PE 3 replicates the query message and forwards it to all PEs participating in the VPLS instance (i.e., PE 1, PE 2, PE 4). - PE 3 notes that there is already a directly connected Querier. Basically, it keeps a state of {[McastRouters: AC4, PW3to4], [Querier: AC4], [(*,G); Hosts:]}, if it is a group specific query. It keeps a state of {[McastRouters: AC4, PW3to4], [Querier: AC4], [(*,*); Hosts:]}, if it is a general query. - All PEs then forward the query to ACs which are part of the VPLS instance. - At this point all PEs learn the place of the Querier. For instance, for PE 1 it is behind PW1to3, for PE 2 behind PW2to3, for PE 3 behind AC4, for PE 4 behind PW3to4. - Suppose that all hosts (Host 1, Host 2, and Host 3) want to participate in the multicast group. - Host 2 first (for the sake of the example) sends a membership report to the multicast group (e.g., IP: 239.1.1.1, MAC: 01-00- 5E-01-01-01), of which Host 2 wants to be a member. - PE 2 replicates the membership report message and forwards it to all PEs participating in the VPLS instance (i.e., PE 1, PE 3, PE 4). - PE 2 notes that there is a directly connected host, which is willing to participate in the multicast group and updates its state to {[McastRouters: PW2to3, PW2to4], [Querier: PW2to3], [(*,G); Hosts:AC2]}. Guideline 1: A PE MUST forward a membership report message to ACs that are part of "McastRouters" state. This is necessary to avoid report suppression for other members in order for the PEs to construct correct states and to not have any orphan receiver hosts. [Page 8]
Internet Draft draft-serbest-l2vpn-vpls-mcast-01.txt November, 2004 There are still some scenarios that can result in orphan receivers. For instance, a multicast router and some hosts could be connected to a customer layer-2 switch, and that layer-2 switch can be connected to a PE via an AC. In such scenario, the customer layer-2 switch MUST perform IGMP snooping as well, and it MUST NOT forward the IGMP report messages coming from the PE to the hosts directly connected to it. There can be some cases such that the layer-2 switch does not have IGMP snooping capability or that device is a dummy hub/bridge. In such cases, one can statically configure the AC, through which the IGMP incapable layer-2 device is connected, to be a (S,G)/(*,G) member on the PE. This way, multicast traffic will always be sent to the hosts connected to that layer-2 device, even they donÆt send joins because of join suppression. Continuing with the example: - PE 2 does not forward the membership report of Host 2 to Host 3. - Per the guideline above, PE 1 does not forward the membership report of Host 2 to Host 1. - Per the guideline above, PE 3 does forward the membership report of Host 2 to Router 1 (the Querier). - PE 3 notes that there is a host in the VPLS instance, which is willing to participate in the multicast group and updates its state to {[McastRouters: AC4, PW3to4], [Querier: AC4], [(*,G); Hosts: PW2to3]} regardless of the type of the query. - LetÆs assume that Host 1 subsequently sends a membership report to the same multicast group. - PE 1 replicates the membership report message and forwards it to all PEs participating in the VPLS instance (i.e., PE 2, PE 3, PE 4). - PE 1 notes that there is a directly connected host, which is willing to participate in the multicast group. Basically, it keeps a state of {[McastRouters: PW1to3, PW1to4], [Querier: PW1to3], [(*,G); Hosts: AC1,PW1to2]}. - Per Guideline 1, PE 2 does not forward the membership report of Host 1 to Host 2 and Host 3. - PE 3 and PE 4 receive the membership report message of Host 1 and check their states. Per Guideline 1, they send the report to Router 1 and Router 2 respectively. They also update their states to reflect Host 1. - Now, Host 3 sends a membership report to the same multicast group. - PE 2 updates its state to {[McastRouters: PW2to3, PW2to4], [Querier: PW2to3], [(*,G); Hosts: AC2,AC3,PW1to2]}. It then floods the report message to all PEs participating in the VPLS instance. Per Guideline 1, PE 3 forwards the membership report [Page 9]
Internet Draft draft-serbest-l2vpn-vpls-mcast-01.txt November, 2004 of Host 3 to Router 1, and PE 4 forwards the membership report of Host 3 to Router 2. At this point, all PEs have necessary states to ensure that no multicast traffic will be sent to sites with no members. The previous steps work the same way for IGMPv1 and IGMPv2, when the query is general or source specific. The group and source specific query for IGMPv3 is considered separately below. In IGMPv3, there is no simple membership join or leave report. IGMPv3 reports are one of IS_INCLUDE, IS_EXCLUDE, ALLOW, BLOCK, TO_INCLUDE, TO_EXCLUDE. The PEs MUST implement the "router behavior" portion of the state machine defined in Section 6 of [RFC3376]. The IGMP snooping mechanism for joining a multicast group (for IGMPv3) works as follows: - The Querier sends a membership query to all hosts (IP:224.0.0.1, MAC:01-00-5E-00-00-01). The membership query is group and source specific query with a list of sources (e.g., S1, S2, .., Sn). - PE 3 replicates the query message and forwards it to all PEs participating in the VPLS instance (i.e., PE 1, PE 2, PE 4). - PE 3 notes that there is already a directly connected Querier. Basically, it keeps a state of {[McastRouters: AC4, PW3to4], [Querier: AC4], [(S1,G); Hosts: ], [(S2,G); Hosts: ], .., [(Sn,G); Hosts: ]}. - All PEs then forward the query to ACs which are part of the VPLS instance. - At this point, all PEs learn the place of the Querier. - Suppose that all hosts (Host 1, Host 2, and Host 3) want to participate in the multicast group. Host 1 and Host 2 want to subscribe to (Sn,G), and Host 3 wants to subscribe to (S3,G). - Host 2 first (for the sake of the example) sends a membership report message with group record type IS_INCLUDE for (Sn,G) to IP address of 224.0.0.22 (MAC:01-00-5E-00-00-16). - PE 2 replicates the membership report message and forwards it to all PEs participating in the VPLS instance (i.e., PE 1, PE 3, PE 4). - PE 2 notes that there is a directly connected host, which is willing to participate in the multicast group and updates its state to {[McastRouters: PW2to3, PW2to4], [Querier: PW2to3], [(S1,G); Hosts: ], [(S2,G); Hosts: ], .., [(Sn,G); Hosts: AC2]}. - Per Guideline 1, PE 2 does not forward the membership report of Host 2 to Host 3. [Page 10]
Internet Draft draft-serbest-l2vpn-vpls-mcast-01.txt November, 2004 - Per Guideline 1, PE 1 does not forward the membership report of Host 2 to Host 1. - Per Guideline 1, PE 3 does forward the membership report of Host 2 to Router 1 (the Querier). - Per Guideline 1, PE 4 does forward the membership report of Host 2 to Router 2. - PE 3 notes that there is a host in the VPLS instance, which is willing to participate in the multicast group. Basically, it updates its state to {[McastRouters: AC4, PW3to4], [Querier: AC4], [(S1,G); Hosts: ], [(S2,G); Hosts: ], .., [(Sn,G); Hosts: PW2to3]}. - Likewise, PE 4 updates its state to {[McastRouters: PW3to4, AC5], [Querier: PW3to4], [(S1,G); Hosts: ], [(S2,G); Hosts: ], .., [(Sn,G); Hosts: PW2to4]}. - LetÆs say Host 1 now sends a membership report message with group record type IS_INCLUDE for (Sn,G). - Similar procedures are followed by PEs as explained in the previous steps. For instance, PE 1 updates its state to {[McastRouters: PW1to3, PW1to4], [Querier: PW1to3], [(S1,G); Hosts: ], [(S2,G); Hosts: ], .., [(Sn,G); Hosts: PW1to2, AC1]}. PE 3 updates its state to {[McastRouters: AC4, PW3to4], [Querier: AC4], [(S1,G); Hosts: ], [(S2,G); Hosts: ], .., [(Sn,G); Hosts: PW2to3, PW1to4]}. - Finally, Host 3 sends a membership report message with group record type IS_INCLUDE for (S3,G). - PE 2 replicates the membership report message and forwards it to all PEs participating in the VPLS instance (i.e., PE 1, PE 3, PE 4). - Per Guideline 1, PE 2 does not forward the membership report of Host 3 to Host 2. - Per Guideline 1, PE 1 does not forward the membership report of Host 3 to Host 1. - Per Guideline 1, PE 3 does forward the membership report of Host 3 to Router 1. - Per Guideline 1, PE 4 does forward the membership report of Host 3 to Router 2. - All PEs update their states accordingly. For instance, PE 2 updates its state to {[McastRouters: PW2to3, PW2to4], [Querier: PW2to3], [(S1,G); Hosts: ], .., [(S3,G); Hosts: AC3], .., [(Sn,G); Hosts: PW1to2, AC2]}. PE 4 updates its state to {[McastRouters: AC5, PW3to4], [Querier: PW3to4], [(S1,G); Hosts: ], .., [(S3,G); Hosts: PW2to4], .., [(Sn,G); Hosts: PW1to4, PW2to4]}. At this point, all PEs have necessary states to not send multicast traffic to sites with no members. [Page 11]
Internet Draft draft-serbest-l2vpn-vpls-mcast-01.txt November, 2004 Based on above description of IGMPv3 based snooping for VPLS, one may conclude that the PEs MUST have the capability to store (S,G) state and MUST forward/replicate traffic accordingly. This is, however, not MANDATORY. A PE MAY only keep (*,G) based states rather than on a per (S,G) basis with the understanding that this will result in a less efficient IP multicast forwarding within each VPLS instance. Guideline 2: If a PE receives unsolicited report message and if it does not possess a state for that particular multicast group, it MUST flood that unsolicited membership report message to all PEs participating in the VPLS instance, as well as to the multicast router if it is locally attached. 5.2.3 IGMP Leave The IGMP snooping mechanism for leaving a multicast group works as follows: - In the case of IGMPv2, when a PE receives a leave (*,G)/(S,G) message from a host via its AC, it removes the AC from its state. - In the case of IGMPv3, when a PE receives a membership report message with group record type of IS_EXCLUDE or TO_EXCLUDE or BLOCK for (S,G) from a host via its AC, it removes the AC from its state. In the following guideline, a "leave (*,G)/(S,G) message" also means IGMPv3 membership report message with group record type of IS_EXCLUDE or TO_EXCLUDE or BLOCK for (S,G). Guideline 3: A PE MUST NOT forward a leave (*,G)/(S,G) message to ACs participating in the VPLS instance, If the PE still has locally connected hosts or hosts connected over a H-VPLS spoke in its state. Guideline 4: A PE MUST forward a leave (*,G)/(S,G) message to all PEs participating in the VPLS instance. A PE MAY forward the leave (*,G)/(S,G) message to the "McastRouters" ONLY, if there are no member hosts in its state. Guideline 5: In case of IGMPv1, If a PE does not receive a membership report from an AC for the three consecutive queries, the PE MUST remove the AC from its state. In case of IGMPv2 and IGMPv3, If a PE does not receive a membership report from an AC for the two consecutive "Last Member Query Intervals", the PE MUST remove the AC from its state. [Page 12]
Internet Draft draft-serbest-l2vpn-vpls-mcast-01.txt November, 2004 5.2.4 Failure Scenarios Up to now, we did not consider any failures, which we will focus in this section. - In case the Querier fails (e.g., AC to the querier fails), another router in the VPLS instance will be selected as the Querier. The new Querier will be sending queries. In such circumstances, the IGMP snooping states in the PEs will be updated/overwritten by the same procedure explained above. - In case a Multicast router fails, the IGMP snooping states in the PEs will be updated/overwritten by the multicast router discovery procedures provided in Section 5.2.1. - In case a host fails (e.g., AC to the host fails), a PE removes the host from its IGMP snooping state for that particular multicast group. Guidelines 3, 4 and 5 still apply here. - In case a PW (which is in IGMP snooping state) fails, the PEs will remove the PW from their IGMP snooping state. For instance, if PW1to3 fails, then PE 1 will remove PW1to3 from its state as the Querier connection, and PE 3 will remove PW1to3 from its state as one of the host connections. Guidelines 3, 4 and 5 still apply here. After PW is restored, the IGMP snooping states in the PEs will be updated/overwritten by the same procedure explained above. One can implement a dead timer before making any changes to IGMP snooping states upon PW failure. In that case, IGMP snooping states will be altered if the PW can not be restored before the dead timer expires. 5.3 PIM Snooping for VPLS IGMP snooping procedures described above provide efficient delivery of IP multicast traffic in a given VPLS service when end stations are connected to the VPLS. However, when VPLS is offered as a WAN service it is likely that the CE devices are routers and would run PIM between them. To provide efficient IP multicasting in such cases, it is necessary that the PE routers offering the VPLS service do PIM snooping. This section describes the procedures for PIM snooping. PIM is a multicast routing protocol, which runs exclusively between routers. PIM shares many of the common characteristics of a routing protocol, such as discovery messages (e.g., neighbor discovery using Hello messages), topology information (e.g., multicast tree), and error detection and notification (e.g., dead timer and designated router election). On the other hand, PIM does not participate in any kind of exchange of databases, as it uses the unicast routing table to provide reverse path information for building multicast trees. There are a few variants of PIM. In PIM-DM ([PIM-DM]), multicast data is pushed towards the members similar to broadcast mechanism. PIM-DM constructs a separate delivery tree for each [Page 13]
Internet Draft draft-serbest-l2vpn-vpls-mcast-01.txt November, 2004 multicast group. As opposed to PIM-DM, other PIM versions (PIM-SM [RFC2362], PIM-SSM [PIM-SSM], and BIDIR-PIM [BIDIR-PIM]) invokes a pull methodology instead of push technique. PIM routers periodically exchange Hello messages to discover and maintain stateful sessions with neighbors. After neighbors are discovered, PIM routers can signal their intentions to join/prune specific multicast groups. This is accomplished by having downstream routers send an explicit join message (for the sake of generalization, consider Graft messages for PIM-DM as join messages) to the upstream routers. The join/prune message can be group specific (*,G) or group and source specific (S,G). In PIM snooping, a PE snoops on the PIM message exchange between routers, and builds its multicast states. Based on the multicast states, it forwards IP multicast traffic accordingly to avoid unnecessary flooding. In the following, the mechanisms involved for implementing PIMv2 ([RFC2362]) snooping in VPLS are specified. PIMv1 is out of the scope of this document. Please refer to Figure 2 as an example of VPLS with PIM snooping. VPLS Instance +------+ AC1 +------+ +------+ AC4 +------+ |Router|-----| PE |-------------| PE |-----|Router| | 1 | | 1 |\ PW1to3 /| 3 | | 4 | +------+ +------+ \ / +------+ +------+ | \ / | | \ / | | \ /PW2to3 | | \ / | PW1to2| \ |PW3to4 | / \ | | / \PW1to4 | | / \ | | / \ | +------+ +------+ / \ +------+ +------+ |Router| | PE |/ PW2to4 \| PE | |Router| | 2 |-----| 2 |-------------| 4 |-----| 5 | +------+ AC2 +------+ +------+ AC5 +------+ | |AC3 +------+ |Router| | 3 | +------+ Figure 2 Reference Diagram for PIM Snooping for VPLS [Page 14]
Internet Draft draft-serbest-l2vpn-vpls-mcast-01.txt November, 2004 In the following sub-sections, snooping mechanisms for each variety of PIM are specified. 5.3.1 PIM-DM The characteristics of PIM-DM is flood and prune behavior. Shortest path trees are built as a multicast source starts transmitting. In Figure 2, the multicast source is behind Router 4, and all routers have at least one receiver except Router 3 and Router 5. 5.3.1.1 Discovering Multicast Routers The PIM-DM snooping mechanism for neighbor discovery works as follows: - To establish PIM neighbor adjacencies, PIM multicast routers (all routers in this example) send PIM Hello messages to the ALL PIM Routers group address (IPv4: 224.0.0.13, MAC: 01-00-5E- 00-00-0D) on every PIM enabled interfaces. The IPv6 ALL PIM Routers group is "ff02::d". In addition, PIM Hello messages are used to elect Designated Router for a multi-access network. In PIM-DM, the DR acts as the Querier if IGMPv1 is used. Otherwise, DR has no function in PIM-DM. Guideline 6: PIM Hello messages MUST be flooded in the VPLS instance. A PE MUST populate its "PIM Neighbors" list according to the snooping results. This is a general PIM snooping guideline and applies to all variants of PIM snooping. Guideline 7: For PIM-DM only. The "Flood to" list is populated with the ACs/PWs in the "PIM Neighbors" list. Changes to the "PIM Neighbors" list MUST be replicated to the "Flood to" list. - Every router starts sending PIM Hello messages. Per Guideline 6, every PE replicates Hello messages and forwards them to all PEs participating in the VPLS instance. - Based on PIM Hello exchanges PE routers populate PIM snooping states as follows. PE 1: {[(,); Source:; Flood to: AC1, PW1to2, PW1to3, PW1to4], [PIM Neighbors: (Router 1,AC1), (Router 2,Router 3,PW1to2), (Router 4,PW1to3), (Router 5,PW1to4)] }, PE 2: {[(,); Source:; Flood to: AC2, AC3, PW1to2, PW2to3, PW2to4], [PIM Neighbors: (Router 1,PW1to2), (Router 2,AC2), (Router 3,AC3), (Router 4,PW2to3), (Router 5,PW2to4)]}, PE 3: {[(,); Source:; Flood to: AC4, PW1to3, PW2to3, PW3to4], [PIM Neighbors: (Router 1,PW1to3), (Router 2,Router 3,PW2to3), (Router 4,AC4), (Router 5,PW3to4)]}, PE 4: {[(,); Source:; Flood to: AC5, PW1to4, PW2to4, PW3to4], [PIM Neighbors: (Router 1,PW1to4), (Router 2,Router 3,PW2to4), (Router 4,PW3to4), [Page 15]
Internet Draft draft-serbest-l2vpn-vpls-mcast-01.txt November, 2004 (Router 5,AC5)]}. The original "Flood to" list is populated with ACs/PWs in the PIM neighbor list per Guideline 7.. - PIM Hello messages contain a Holdtime value, which tells the receiver when to expire the neighbor adjacency (which is three times the Hello period). Guideline 8: If a PE does not receive a Hello message from a router within its Holdtime, the PE MUST remove that router from the PIM snooping state. If a PE receives a Hello message from a router with Holdtime value set to zero, the PE MUST remove that router from the PIM snooping state immediately. PEs MUST track the Hello Holdtime value per PIM neighbor. 5.3.1.2 PIM-DM Multicast Forwarding The PIM-DM snooping mechanism for multicast forwarding works as follows: - When the source starts sending traffic to multicast group (S,G), PE 3 updates its state to PE 3: {[(S,G) ; Source: (Router 4,AC4); Flood to: PW1to3, PW2to3, PW3to4], [PIM Neighbors: (Router 1,PW1to3), (Router 2,Router 3,PW2to3), (Router 4,AC4), (Router 5,PW3to4)]}. AC4 is removed from the "Flood to" list for (S,G), since it is where the multicast traffic comes from. Guideline 9: Multicast traffic MUST be replicated per PW and AC basis, i.e., even if there are more than one PIM neighbor behind a PW/AC, only one replication MUST be sent to that PW/AC. - PE 3 replicates the multicast traffic and sends it to the other PE routers in its "Flood to" list. - Consequently, all PEs update their states as follows. PE 1: {[(S,G); Source: (Router 4,PW1to3); Flood to: AC1], [PIM Neighbors: (Router 1,AC1), (Router 2,Router 3,PW1to2), (Router 4,PW1to3), (Router 5,PW1to4)]}, PE 2: {[(S,G); Source: (Router 4,PW2to3); Flood to: AC2, AC3], [PIM Neighbors: (Router 1,PW1to2), (Router 2,AC2), (Router 3,AC3), (Router 4,PW2to3), (Router 5,PW2to4)]}, PE 4: {[(S,G); Source: (Router 4,PW3to4); Flood to: AC5], [PIM Neighbors: (Router 1,PW1to4), (Router 2,Router 3,PW2to4), (Router 4,PW3to4), (Router 5,AC5)]}. 5.3.1.3 PIM-DM Pruning At this point all the routers (Router 1, Router 2,Router 3, Router 5) receive the multicast traffic. - However, Router 3 and Router 5 do not have any members for that multicast group, so they send prune messages to leave the [Page 16]
Internet Draft draft-serbest-l2vpn-vpls-mcast-01.txt November, 2004 multicast group to the ALL PIM Routers group. PE 2 updates its state to PE 2: {[(S,G); Source: (Router 4,PW2to3); Flood to: AC2], [PIM Neighbors: (Router 1,PW1to2), (Router 2,AC2), (Router 3,AC3), (Router 4,PW2to3), (Router 5,PW2to4)]}. PE 4 also remove Router 3 and Router 5 from its state as well. Guideline 10: For PIM-DM only. PIM prune messages MUST be flooded in the VPLS instance. - PE 2 and PE 4 then flood the prune message and forward it to all PEs participating in the VPLS instance per Guideline 10. PE 4 updates its state to PE 4: {[(S,G); Source: (Router 4,AC4); Flood to:], [PIM Neighbors: (Router 1,PW1to4), (Router 2,Router 3,PW2to4), (Router 4,PW3to4), (Router 5,AC5)]}. - PIM-DM prune messages contain a Holdtime value, which specifies how many seconds the prune state should last. Guideline 11: For PIM-DM only. A PE MUST keep the prune state for a PW/AC according to the Holdtime in the prune message, unless a corresponding Graft message is received. - Upon receiving the prune messages, each PE updates its state accordingly. PE 1: {[(S,G); Source: (Router 4,PW1to3); Flood to: AC1], [PIM Neighbors: (Router 1,AC1), (Router 2,Router 3, PW1to2), (Router 4,PW1to3), (Router 5,PW1to4)]}, PE 2: {[(S,G); Source: (Router 4,PW2to3); Flood to: AC2], [PIM Neighbors: (Router 1,PW1to2), (Router 2,AC2), (Router 3,AC3), (Router 4,PW2to3), (Router 5,PW2to4)]}, PE 3: {[(S,G); Source: (Router 4,AC4); Flood to: PW1to3, PW2to3], [PIM Neighbors: (Router 1,PW1to3), (Router 2,Router 3,PW2to3), (Router 4,AC4), (Router 5, PW3to4)]}, PE 4: {[(S,G); Source: (Router 4,PW3to4); Flood to:], [PIM Neighbors: (Router 1,PW1to4), (Router 2,Router 3,PW2to4), (Router 4,PW3to4), (Router 5,AC5)]}. Guideline 12: For PIM-DM only. To avoid overriding joins, a PE SHOULD suppress the PIM prune messages to directly connected routers (i.e., ACs), as long as there is a PW/AC in its corresponding "Flood to" list. - In this case, PE 1, PE 2, and PE 3 do not forward the prune messages to their directly connected routers. 5.3.1.4 PIM-DM Grafting The multicast traffic is now flowing only to points in the network where receivers are present. [Page 17]
Internet Draft draft-serbest-l2vpn-vpls-mcast-01.txt November, 2004 Guideline 13: For PIM-DM only. A PE MUST remove the AC/PW from its corresponding prune state when it receives a graft message from the AC/PW. That is, the corresponding AC/PW MUST be added to the "Flood to" list. Guideline 14: For PIM-DM only. PIM-DM graft messages MUST be forwarded based on the destination MAC address. If the destination MAC address is 01-00-5E-00-00-0D, then the graft message MUST be flooded in the VPLS instance. - For the sake of example, suppose now Router 3 has a receiver the multicast group (S,G). Assuming Router 3 sends a graft message in IP unicast to Router 4 to restart the flow of multicast traffic. PE 2 updates its state to PE 2: {[(S,G); Source: (Router 4,PW2to3); Flood to: AC2, AC3], [PIM Neighbors: (Router 1,PW1to2), (Router 2,AC2), (Router 3,AC3), (Router 4,PW2to3), (Router 5,PW2to4)]}. PE 2 then forwards the graft message to PE 3 according to Guideline 14. - Upon receiving the graft message, PE 3 updates its state accordingly to PE 3: {[(S,G); Source: (Router 4,AC4); Flood to: PW1to3, PW2to3], [PIM Neighbors: (Router 1,PW1to3), (Router 2,Router 3,PW2to3), (Router 4,AC4), (Router 5,PW3to4)]}. 5.3.1.5 Failure Scenarios Guideline 15: PIM Assert messages MUST be flooded in the VPLS instance. Guideline 16: If an AC/PW goes down, a PE MUST remove it from its PIM snooping state. Failures can be easily handled in PIM-DM snooping, as it uses push technique. If an AC or a PW goes down, PEs in the VPLS instance will remove it from their snooping state (if the AC/PW is not already pruned). After the AC/PW comes back up, it will be automatically added to the snooping state by PE routers, as all PWs/ACs MUST be in the snooping state, unless they are pruned later on. 5.3.2 PIM-SM The key characteristics of PIM-SM is explicit join behavior. In this model, the multicast traffic is only sent to locations that specifically request it. The root node of a tree is the Rendezvous Point (RP) in case of a shared tree or the first hop router that is directly connected to the multicast source in the case of a shortest path tree. In Figure 2, the RP is behind Router 4, and all routers have at least one member except Router 3 and Router 5. [Page 18]
Internet Draft draft-serbest-l2vpn-vpls-mcast-01.txt November, 2004 As in the case with IGMPv3 snooping, we assume that the PEs have the capability to store (S,G) states for PIM-SM snooping and forward/replicate traffic accordingly. This is not mandatory. An implementation, can fall back to (*,G) states, if its hardware can not support it. In such case, the efficiency of multicast forwarding will be less. 5.3.2.1 Discovering Multicast Routers The PIM-SM snooping mechanism for neighbor discovery works the same way as the procedure defined in PIM-DM section, with the exception of PIM-DM only guidelines. - Based on PIM Hello exchanges PE routers populate PIM snooping states as follows. PE 1: {[(,); Flood to:], [PIM Neighbors: (Router 1,AC1), (Router 2,Router 3,PW1to2), (Router 4,PW1to3), (Router 5,PW1to4)]}, PE 2: {[(,); Flood to:], [PIM Neighbors: (Router 1,PW1to2), (Router 2,AC2), (Router 3,AC3), (Router 4,PW2to3), (Router 5,PW2to4)]}, PE 3: {[(,); Flood to:], [PIM Neighbors: (Router 1,PW1to3), (Router 2,Router 3,PW2to3), (Router 4,AC4), (Router 5,PW3to4)]}, PE 4: {[(,); Flood to:], [PIM Neighbors: (Router 1,PW1to4), (Router 2,Router 3,PW2to4), (Router 4,PW3to4), (Router 5,AC5)]}. For PIM-SM to work properly, all routers within the domain must use the same mappings of group addresses to RP addresses. Currently, there are three methods for RP discovery: 1. Static RP configuration, 2, Auto-RP, and 3. PIMv2 Bootstrap Router mechanism. Guideline 17: Cisco RP-Discovery (IP:224.0.1.40, MAC:01-00-5E-00- 01-28), Cisco-RP-Announce (IP:224.0.1.39, MAC:01-00-5E-00-01-27), all bootstrap router (BSR) (IP:224.0.0.13, MAC:01-00-5E-00-00-0D) messages MUST be flooded in the VPLS instance. 5.3.2.2 PIM-SM (*,G) Join The PIM-SM snooping mechanism for joining a multicast group (*,G) works as follows: Guideline 18: PIM-SM join messages MUST be sent only to the remote PE, which is connected to the router to which the Join is addressed. PIM-SM join messages MUST be sent only to the remote PE, which is connected to the router to which the Join is addressed. The remote PE can be determined by the "Upstream Neighbor Address" field of the Join message. The "Upstream Neighbor Address" can be correlated to a PW or an AC in the "PIM Neighbors" state. By Guideline 18, we are ensuring that the other routers that are part of the VPLS instance do not receive the PIM join messages and will initiate their own [Page 19]
Internet Draft draft-serbest-l2vpn-vpls-mcast-01.txt November, 2004 join messages if they are interested in receiving that particular multicast traffic. - Assume Router 1 wants to join the multicast group (*,G) sends a join message for the multicast group (*,G). PE 1 sends the join message to PE 3 by Guideline 18. Guideline 19: A PE MUST add a PW/AC to its (*,G) "Flood to" list, if it receives a (*,G) join message from the PW/AC. - PE 1 updates their states as follows: PE 1: {[(*,G); Flood to: AC1], [PIM Neighbors: (Router 1,AC1), (Router 2,Router 3,PW1to2), (Router 4,PW1to3), (Router 5,PW1to4)]}. A periodic refresh mechanism is used in PIM-SM to maintain the proper state. PIM-SM join messages contain a Holdtime value, which specifies for how many seconds the join state should be kept. Guideline 20: If a PE does not receive a refresh join message from a PW/AC within its Holdtime, the PE MUST remove the PW/AC from its "Flood to" list. - All PEs update their states accordingly as follows: PE 1: {[(*,G); Flood to: AC1], [PIM Neighbors: (Router 1,AC1), (Router 2,Router 3,PW1to2), (Router 4,PW1to3), (Router 5,PW1to4)]}, PE 2: {[(,); Flood to: ], [PIM Neighbors: (Router 1,PW1to2), (Router 2,AC2), (Router 3,AC3), (Router 4,PW2to3), (Router 5,PW2to4)]}, PE 3: {[(*,G); Flood to: PW1to3], [PIM Neighbors: (Router 1,PW1to3), (Router 2,Router 3,PW2to3), (Router 4,AC4), (Router 5,PW3to4)]}, PE 4: {[(,); Flood to: ], [PIM Neighbors: (Router 1,PW1to4), (Router 2,Router 3,PW2to4), (Router 4,PW3to4), (Router 5,AC5)]}. - After Router 2 joins the same multicast group, the states become as follows: PE 1: {[(*,G); Flood to: AC1], [PIM Neighbors: (Router 1,AC1), (Router 2,Router 3,PW1to2), (Router 4,PW1to3), (Router 5,PW1to4)]}, PE 2: {[(*,G); Flood to: AC2], [PIM Neighbors: (Router 1,PW1to2), (Router 2,AC2), (Router 3,AC3), (Router 4,PW2to3), (Router 5,PW2to4)]}, PE 3: {[(*,G); Flood to: PW1to3, PW2to3], [PIM Neighbors: (Router 1,PW1to3), (Router 2,Router 3,PW2to3), (Router 4,AC4), (Router 5,PW3to4)]}, PE 4: {[(,); Flood to: ], [PIM Neighbors: (Router 1,PW1to4), (Router 2,Router 3,PW2to4), (Router 4,PW3to4), (Router 5,AC5)]}. - For the sake of example, Router 3 joins the multicast group. PE 2 sends the join message to PE 3. [Page 20]
Internet Draft draft-serbest-l2vpn-vpls-mcast-01.txt November, 2004 - Next Router 5 joins the group, and the states are updated accordingly: PE 1: {[(*,G); Flood to: AC1], [PIM Neighbors: (Router 1,AC1), (Router 2,Router 3,PW1to2), (Router 4,PW1to3), (Router 5,PW1to4)]}, PE 2: {[(*,G); Flood to: AC2, AC3], [PIM Neighbors: (Router 1,PW1to2), (Router 2,AC2), (Router 3,AC3), (Router 4,PW2to3), (Router 5,PW2to4)]}, PE 3: {[(*,G); Flood to: PW1to3, PW2to3, PW3to4], [PIM Neighbors: (Router 1,PW1to3), (Router 2,Router 3,PW2to3), (Router 4,AC4), (Router 5,PW3to4)]}, PE 4: {[(*,G); Flood to: AC5],[PIM Neighbors: (Router 1,PW1to4), (Router 2,Router 3,PW2to4), (Router 4,PW3to4), (Router 5,AC5)]} At this point, all PEs have necessary states to not send multicast traffic to sites with no members. 5.3.2.3 PIM-SM Pruning The PIM-SM snooping mechanism for leaving a multicast group works as follows: - Assume Router 5 sends a prune message. Guideline 21: PIM-SM prune messages MUST be flooded in the VPLS instance. Guideline 22: A PE MUST remove a PW/AC from its (*,G) "Flood to" list if it receives a (*,G) prune message from the PW/AC. A prune-delay timer SHOULD be implemented to support prune override. - PE 4 floods the (*,G) prune to the VPLS instance per Guideline 21. PE routers participating in the VPLS instance also forward the (*,G) prune to the ACs, which are connected to the VPLS instance. The states are updated as follows: PE 1: {[(*,G); Flood to: AC1], [PIM Neighbors: (Router 1,AC1), (Router 2,Router 3,PW1to2), (Router 4,PW1to3), (Router 5,PW1to4)]}, PE 2: {[(*,G); Flood to: AC2, AC3], [PIM Neighbors: (Router 1,PW1to2), (Router 2,AC2), (Router 3,AC3), (Router 4,PW2to3), (Router 5,PW2to4)]}, PE 3: {[(*,G); Flood to: PW1to3, PW2to3], [PIM Neighbors: (Router 1,PW1to3), (Router 2,Router 3,PW2to3), (Router 4,AC4), (Router 5,PW3to4)]}, PE 4: {[(,); Flood to: ],[PIM Neighbors: (Router 1,PW1to4), (Router 2,Router 3,PW2to4), (Router 4,PW3to4), (Router 5,AC5)]}. In PIM-SM snooping, prune messages are flooded by PE routers. In such implementation, PE routers may receive overriding join messages, which will not affect anything. [Page 21]
Internet Draft draft-serbest-l2vpn-vpls-mcast-01.txt November, 2004 5.3.2.4 PIM-SM (S,G) Join The PIM-SM snooping mechanism for source and group specific join works as follows: Guideline 23: A PE MUST add a PW/AC to its (S,G) "Flood to" list if it receives a (S,G) join message from the PW/AC. Guideline 24: A PE MUST remove a PW/AC from its (S,G) "Flood to" list if it receives a (S,G) prune message from the PW/AC. A prune-delay timer SHOULD be implemented to support prune override. Guideline 25: A PE MUST prefer (S,G) state to (*,G), if both S and G match. Guideline 26: When a (S,G) is state is first created, the initial "Flood to" list MUST be populated by copying the "Flood to" list from its parent (*,G) state. Guideline 27: In case (*,G) state changes in a PE, all changes to (*,G) state MUST (additions and deletions in "Flood to" list) be replicated to (S,G) state. - Now, we assume Router 5 sends a source and group specific join (S,G). LetÆs assume the source is behind Router 1. PE 4 sends the (S,G) join to PE 1. PE 1 forwards the (S,G) join to AC1. The states are updated as follows: PE 1: {[(*,G); Flood to: AC1], [(S,G); Flood to: AC1,PW1to4], [PIM Neighbors: (Router 1,AC1), (Router 2,Router 3,PW1to2), (Router 4,PW1to3), (Router 5,PW1to4)]}, PE 2: {[(*,G); Flood to: AC2, AC3], [PIM Neighbors: (Router 1,PW1to2), (Router 2,AC2), (Router 3,AC3), (Router 4,PW2to3), (Router 5,PW2to4)]}, PE 3: {[(*,G); Flood to: PW1to3, PW2to3], [PIM Neighbors: (Router 1,PW1to3), (Router 2,Router 3,PW2to3), (Router 4,AC4), (Router 5,PW3to4)]}, PE 4: {[(S,G); Flood to: AC5],[PIM Neighbors: (Router 1,PW1to4), (Router 2,Router 3,PW2to4), (Router 4,PW3to4), (Router 5,AC5)]}. - Afterwards, we assume Router 5 sends a (S,G)RP-bit prune, also known as (S,G,RPT) prune. PE routers flood this prune message and do not take any action. 5.3.2.5 PIM-SM (*,*,RP) State PIM-SM defines a (*,*,RP) state which is used when traffic needs to cross multicast domains. A (*,*,RP) receiver requests all multicast traffic within a PIM domain to be sent to it. If the two multicast domains are both PIM-SM, they can use MSDP to leak multicast routes. But, if one is PIM-SM and the other is PIM-DM (hence, MSDP can not be used), then the border router would initiate a (*,*,RP) join to all RPs in the PIM-SM domain. [Page 22]
Internet Draft draft-serbest-l2vpn-vpls-mcast-01.txt November, 2004 If the customers will configure multiple and different PIM domains, PIM-SM snooping MUST support (*,*,RP) state as well. Depending on how likely scenario this is, future versions may include (*,*,RP) states. 5.3.2.6 Failure Scenarios Failures can be easily handled in PIM-SM snooping, as it employs state-refresh technique. PEs in the VPLS instance will remove any entry for non-refreshing routers from their states. 5.3.2.7 Special Cases for PIM-SM Snooping There are some special cases to consider for PIM-SM snooping. First one is the RP-on-a-stick. The RP-on-a-stick scenario may occur when the Shortest Path Tree and the Shared Tree shares a common Ethernet segment, as all routers will be connected over a multicast access network (i.e., VPLS). Such a scenario will be handled by PIM-SM rules (particularly, the incoming interface can not also appear in the outgoing interface list) very nicely. Second scenario is the turnaround router. The turnaround router scenario occurs when shortest path tree and shared tree share a common path. The router at which these tree merge is the turnaround router. PIM-SM handles this case by proxy (S,G) join implementation by the turnaround router. There can be some scenarios where CE routers can receive duplicate multicast traffic. LetÆs consider the scenario in Figure 3. +------+ AC3 +------+ | PE2 |-----| R3 | /| | | | / +------+ +------+ / | | / | | /PW1to2 | | / | +-----+ / |PW2to3 | Src | / | +-----+ / | | / | | / | | +------+ +------+ / +------+ +------+ | R1 | | PE1 |/ PW1to3 | PE3 | | R4 | | |-----| |-------------| |-----| | +------+ AC1 +------+ +------+ AC4 +------+ | | |AC2 |AC5 +------+ +------+ | R2 | | R5 | +---+ | | | |-----|RP | +------+ +------+ +---+ [Page 23]
Internet Draft draft-serbest-l2vpn-vpls-mcast-01.txt November, 2004 Figure 3 CE Routers Receive Duplicate Traffic In the scenario depicted in Figure 3, both R1 and R2 has two ECMP routes to reach the source Src. Hence, R1 may pick R3 as its next hop ("Upstream Neighbor"), and R2 may pick R4 as its next hop. As a result, both R1 and R2 will receive duplicate traffic. This issue can be solved as follows. PEs can keep the PW/AC that the join message is forwarded to (upstream PW/AC) in "Flood to" list in addition to the PW/AC that the join message is received (downstream PWAC). If the traffic arrives from a different PW/AC, that traffic is not forwarded downstream. Hence, in the example depicted in Figure 3 where source is dual homed to R3 and R4, R1 will receive (S,G) traffic if it comes from PW1to2, and R2 will receive (S,G) traffic if it comes from PW1to3. Again, in Figure 3, R1 may send (S,G) join to R3 and R2 may send (*,G) join to the RP behind R5. In this scenario as well, both R1 and R2 will receive duplicate traffic, as Guideline 25 will be no help to prevent it. In this case, where R1 joins for (S,G), and R2 joins for (*,G), we can do the following. The PEs SHOULD keep the upstream PW/AC in the state as described above. In addition, the PEs need to act on (S,G,RPT) prunes and remove the related upstream PW/AC from "Flood to" list of (S,G) state copied from (*,G) state. As a result, Ces will not receive duplicate traffic. However, there will still be bandwidth waste as the egress PE takes care of the duplicate traffic problem. We can further enhance the proposal by triggering Assert mechanism in CE routers. The PE which detects the duplicate traffic problem can simply remove the snooping state for that particular multicast group, and can send out "flush" message to other PEs participating in the VPLS instance. In return, other PEs also flush their snooping state for that multicast group. As a result, all the PEs will flood the multicast traffic in the VPLS instance (by Rule 3). Consequently, CEs will do Assert. The flush message TLV can be sent over the targeted LDP sessions running among PEs. Future versions will include the details. 5.3.3 PIM-SSM The key characteristics of PIM-SSM is explicit join behavior, but it eliminates the shared tree and the rendezvous point in PIM-SM. In this model, a shortest path tree for each (S,G) is built with the first hop router (that is directly connected to the multicast source) being the root node. PIM-SSM is ideal for one-to-many multicast services. In Figure 2, S1 is behind Router 1, and S4 is behind Router 4. Routers 2 and 4 want to join (S1,G), while Router 5 wants to join (S4,G). [Page 24]
Internet Draft draft-serbest-l2vpn-vpls-mcast-01.txt November, 2004 We assume that the PEs have the capability to store (S,G) states for PIM-SSM snooping and constrain multicast flooding scope accordingly. An implementation, can fall back to (*,G) states, if its hardware can not support it. In such case, the efficiency of multicast forwarding will be less. 5.3.3.1 Discovering Multicast Routers The PIM-SSM snooping mechanism for neighbor discovery works the same way as t procedure defined in PIM-DM section, with the exception of PIM-DM only guidelines. - Based on PIM Hello exchanges PE routers populate PIM snooping states as follows. PE 1: {[(,); Flood to:], [PIM Neighbors: (Router 1,AC1), (Router 2,Router 3,PW1to2), (Router 4,PW1to3), (Router 5,PW1to4)]}, PE 2: {[(,); Flood to:], [PIM Neighbors: (Router 1,PW1to2), (Router 2,AC2), (Router 3,AC3), (Router 4,PW2to3), (Router 5,PW2to4)]}, PE 3: {[(,); Flood to:], [PIM Neighbors: (Router 1,PW1to3), (Router 2,Router 3,PW2to3), (Router 4,AC4), (Router 5,PW3to4)]}, PE 4: {[(,); Flood to:], [PIM Neighbors: (Router 1,PW1to4), (Router 2,Router 3,PW2to4), (Router 4,PW3to4), (Router 5,AC5)]}. 5.3.3.2 Guidelines for PIM-SSM Snooping PIM-SSM snooping is actually simpler than PIM-SM and only the following guidelines (some of which are repetitions from PIM-SM section) apply. Guideline 28: A PE MUST add a PW/AC to its (S,G) "Flood to" list if it receives a (S,G) join message from the PW/AC. Guideline 29: PIM-SSM join messages MUST be sent only to the remote PE, which is connected to the router to which the Join is addressed. Guideline 30: PIM prune messages MUST be flooded in the VPLS instance. Guideline 31: If A PE does not receive a refresh join message from a PW/AC within its Holdtime, the PE MUST remove the PW/AC from its "Flood to" list. Guideline 32: A PE MUST remove a PW/AC from its (S,G) "Flood to" list if it receives a (S,G) prune message from the PW/AC. A prune-delay timer SHOULD be implemented to support prune override. 5.3.3.3 PIM-SSM Join The PIM-SSM snooping mechanism for joining a multicast group works as follows: [Page 25]
Internet Draft draft-serbest-l2vpn-vpls-mcast-01.txt November, 2004 - Assume Router 2 requests to join the multicast group (S1,G). - PE 2 updates its state, and then sends the join message to PE 1. - All PEs update their states as follows: PE 1: {[(S1,G); Flood to: PW1to2], [PIM Neighbors: (Router 1,AC1), (Router 2,Router 3,PW1to2), (Router 4,PW1to3), (Router 5,PW1to4)]}, PE 2: {[(S1,G); Flood to: AC2], [PIM Neighbors: (Router 1,PW1to2), (Router 2,AC2), (Router 3,AC3), (Router 4,PW2to3), (Router 5,PW2to4)]}, PE 3: {[(,); Flood to: ], [PIM Neighbors: (Router 1,PW1to3), (Router 2,Router 3,PW2to3), (Router 4,AC4), (Router 5,PW3to4)]}, PE 4: {[(,); Flood to: ], [PIM Neighbors: (Router 1,PW1to4), (Router 2,Router 3,PW2to4), (Router 4,PW3to4), (Router 5,AC5)]}. - Next, assume Router 4 sends a join (S1,G) message. Following the same procedures, all PEs update their states as follows: PE 1: {[(S1,G); Flood to: PW1to2, PW1to3], [PIM Neighbors: (Router 1,AC1), (Router 2,Router 3,PW1to2), (Router 4,PW1to3), (Router 5,PW1to4)]}, PE 2: {[(S1,G); Flood to: AC2], [PIM Neighbors: (Router 1,PW1to2), (Router 2,AC2), (Router 3,AC3), (Router 4,PW2to3), (Router 5,PW2to4)]}, PE 3: {[(S1,G); Flood to: AC4], [PIM Neighbors: (Router 1,PW1to3), (Router 2,Router 3,PW2to3), (Router 4,AC4), (Router 5,PW3to4)]}, PE 4: {[(,); Flood to: ], [PIM Neighbors: (Router 1,PW1to4), (Router 2,Router 3,PW2to4), (Router 4,PW3to4), (Router 5,AC5)]}. - Then, assume Router 5 requests to join the multicast group (S4,G). After the same procedures are applied, all PEs update their states as follows: PE 1: {[(S1,G); Flood to: PW1to2, PW1to3], [PIM Neighbors: (Router 1,AC1), (Router 2,Router 3,PW1to2), (Router 4,PW1to3), (Router 5,PW1to4)]}, PE 2: {[(S1,G); Flood to: AC2], [PIM Neighbors: (Router 1,PW1to2), (Router 2,AC2), (Router 3,AC3), (Router 4,PW2to3), (Router 5,PW2to4)]}, PE 3: {[(S1,G); Flood to: AC4], [(S4,G); Flood to: PW3to4], [PIM Neighbors: (Router 1,PW1to3), (Router 2,Router 3,PW2to3), (Router 4,AC4), (Router 5,PW3to4)]}, PE 4: {[(S4,G); Flood to: AC5], [PIM Neighbors: (Router 1,PW1to4), (Router 2,Router 3,PW2to4), (Router 4,PW3to4), (Router 5,AC5)]}. 5.3.3.4 PIM-SSM Prune At this point, all PEs have necessary states to not send multicast traffic to sites with no members. The PIM-SSM snooping mechanism for leaving a multicast group works as follows: - Assume Router 2 sends a (S1,G) prune message to leave the multicast group. The prune message gets flooded in the VPLS instance. All PEs update their states as follows: PE 1: [Page 26]
Internet Draft draft-serbest-l2vpn-vpls-mcast-01.txt November, 2004 {[(S1,G); Flood to: PW1to3], [PIM Neighbors: (Router 1,AC1), (Router 2,Router 3,PW1to2), (Router 4,PW1to3), (Router 5,PW1to4)]}, PE 2: {[(,); Flood to: ], [PIM Neighbors: (Router 1,PW1to2), (Router 2,AC2), (Router 3,AC3), (Router 4,PW2to3), (Router 5,PW2to4)]}, PE 3: {[(S1,G); Flood to: AC4], [(S4,G); Flood to: PW3to4], [PIM Neighbors: (Router 1,PW1to3), (Router 2,Router 3,PW2to3), (Router 4,AC4), (Router 5,PW3to4)]}, PE 4: {[(S4,G); Flood to: AC5], [PIM Neighbors: (Router 1,PW1to4), (Router 2,Router 3,PW2to4), (Router 4,PW3to4), (Router 5,AC5)]}. In PIM-SSM snooping, prune messages are flooded by PE routers. In such implementation, PE routers may receive overriding join messages, which will not affect anything. 5.3.3.5 Failure Scenarios Similar to PIM-SSM snooping, failures can be easily handled in PIM- SSM snooping, as it employs state-refresh technique. The PEs in the VPLS instance will remove entry for non-refreshing routers from their states. 5.3.3.6 Special Cases for PIM-SSM Snooping The scenarios with duplicate traffic as depicted in Figure 3 apply to PIM-SSM snooping as well. Again, the issue can be solved by the method described in Section 5.3.2.7. 5.3.4 Bidirectional-PIM (BIDIR-PIM) BIDIR-PIM is a variation of PIM-SM. The main differences between PIM-SM and Bidirectional-PIM are as follows: - There are no source-based trees, and source-specific multicast is not supported (i.e., no (S,G) states) in BIDIR-PIM. - Multicast traffic can flow up the shared tree in BIDIR-PIM. - To avoid forwarding loops, one router on each link is elected as the Designated Forwarder (DF) for each RP in BIDIR-PIM. The main advantage of BIDIR-PIM is that it scales well for many-to- many applications. However, the lack of source-based trees means that multicast traffic is forced to remain on the shared tree. In Figure 2, the RP for (*,G4) is behind Router 4, and the RP for (*,G1) is behind Router 1. Router 2 and Router 4 want to join (*,G1), whereas Router 5 wants to join (*,G4). On the VPLS instance, Router 4 is the DF for the RP of (*,G4), and Router 1 is the DF of the RP for (*,G1). 5.3.4.1 Discovering Multicast Routers The PIM-SSM snooping mechanism for neighbor discovery works the same way as t procedure defined in PIM-DM section, with the exception of PIM-DM only guidelines. [Page 27]
Internet Draft draft-serbest-l2vpn-vpls-mcast-01.txt November, 2004 - Based on PIM Hello exchanges PE routers populate PIM snooping Based on PIM Hello exchanges PE routers populate PIM snooping states as follows. PE 1: {[(,); Upstream to:; Downstream to:], [PIM Neighbors: (Router 1,AC1), (Router 2,Router 3,PW1to2), (Router 4,PW1to3), (Router 5,PW1to4)], [(,), DF:]}, PE 2: {[(,); Upstream to:; Downstream to:], [PIM Neighbors: (Router 1,PW1to2), (Router 2,AC2), (Router 3,AC3), (Router 4,PW2to3), (Router 5,PW2to4)], [(,), DF:]}, PE 3: {[(,); Upstream to:; Downstream to:], [PIM Neighbors: (Router 1,PW1to3), (Router 2,Router 3,PW2to3), (Router 4,AC4), (Router 5,PW3to4)], [(,), DF:]}, PE 4: {[(,); Upstream to:; Downstream to:], [PIM Neighbors: (Router 1,PW1to4), (Router 2,Router 3,PW2to4), (Router 4,PW3to4), (Router 5,AC5)], [(,), DF:]}. For BIDIR-PIM to work properly, all routers within the domain must know the address of the RP. There are three methods to do that: 1. Static RP configuration, 2, Auto-RP, and 3. PIMv2 Bootstrap. Guideline 17 applies here as well. During RP discovery time, PIM routers elect DF per subnet for each RP. The algorithm to elect the DF is as follows: all PIM neighbors in a subnet advertise their unicast route to elect the RP and the router with the best route is elected. Guideline 33: All PEs MUST snoop the DF elections messages and determine the DF for each [(*,G),RP)] pair. The "Upstream" list MUST be updated with PW/AC that leads to the DF. When the DF changes, the "Upstream" list MUST be updated accordingly. - Based on DF election messages, PE routers populate PIM snooping states as follows: PE 1: {[(*,G1); Upstream to: AC1; Downstream to:], [(*,G4); Upstream to: PW1to3; Downstream to:], [PIM Neighbors: (Router 1,AC1), (Router 2,Router 3,PW1to2), (Router 4,PW1to3), (Router 5,PW1to4)], [(*,G1), DF: AC1], [(*,G4), DF: PW1to4]}, PE 2: {[(*,G1); Upstream to: PW1to2; Downstream to:], [(*,G4); Upstream to: PW2to3; Downstream to:], [PIM Neighbors: (Router 1,PW1to2), (Router 2,AC2), (Router 3,AC3), (Router 4,PW2to3), (Router 5,PW2to4)], [(*,G1), DF:PW1to2], [(*,G4), DF:PW2to3]}, PE 3: {[(*,G1); Upstream to: PW1to3; Downstream to:], [(*,G4); Upstream to: AC4; Downstream to:], [PIM Neighbors: (Router 1,PW1to3), (Router 2,Router 3,PW2to3), (Router 4,AC4), (Router 5,PW3to4)], [(*,G1), DF: PW1to3], [(*,G4), DF: AC4]}, PE 4: {[(*,G1); Upstream to: PW1to4; Downstream to:], [(*,G4); Upstream to: PW3to4; Downstream to:], [PIM Neighbors: (Router 1,PW1to4), (Router 2,Router 3,PW2to4), (Router 4,PW3to4), (Router 5,AC5)], [(*,G1), DF: PW1to4], [(*,G4), DF: PW3to4]}. [Page 28]
Internet Draft draft-serbest-l2vpn-vpls-mcast-01.txt November, 2004 5.3.4.2 Guidelines for BIDIR-PIM Snooping The BIDIR-PIM snooping for Join and Prune messages is similar to PIM-SM and the following guidelines (some of which are repetitions from PIM-SM section) apply. Guideline 34: A PE MUST add a PW/AC to its (*,G) "Downstream" list if it receives a (*,G) join message from the PW/AC. Guideline 35: BIDIR-PIM join messages MUST be sent only to the remote PE, which is connected to the router to which the Join is addressed. Guideline 36: BIDIR-PIM prune messages MUST be flooded in the VPLS instance. Guideline 37: If A PE does not receive a refresh join message from a PW/AC within its Holdtime, the PE MUST remove the PW/AC from its "Downstream" list. Guideline 38: A PE MUST remove a PW/AC from its (*,G) "Downstream" list if it receives a (*,G) prune message from the PW/AC. A prune-delay timer SHOULD be implemented to support prune override. Guideline 39: A PE MUST replicate multicast traffic for (*,G) to the members in its (*,G) "Upstream" and "Downstream" lists. 5.3.4.3 BIDIR-PIM Join The BIDIR-PIM snooping mechanism for joining a multicast group works as follows: - Assume Router 2 wants to join the multicast group (*,G1). PE 2 sends the join message PE 1. All PEs update their states as follows: PE 1: {[(*,G1); Upstream to: AC1; Downstream to: PW1to2], [(*,G4); Upstream to: PW1to3; Downstream to:], [PIM Neighbors: (Router 1,AC1), (Router 2,Router 3,PW1to2), (Router 4,PW1to3), (Router 5,PW1to4)], [(*,G1), DF: AC1], [(*,G4), DF: PW1to4]}, PE 2: {[(*,G1); Upstream to: PW1to2; Downstream to: AC2], [(*,G4); Upstream to: PW2to3; Downstream to:], [PIM Neighbors: (Router 1,PW1to2), (Router 2,AC2), (Router 3,AC3), (Router 4,PW2to3), (Router 5,PW2to4)], [(*,G1), DF:PW1to2], [(*,G4), DF:PW2to3]}, PE 3: {[(*,G1); Upstream to: PW1to3; Downstream to: ], [(*,G4); Upstream to: AC4; Downstream to:], [PIM Neighbors: (Router 1,PW1to3), (Router 2,Router 3,PW2to3), (Router 4,AC4), (Router 5,PW3to4)], [(*,G1), DF: PW1to3], [(*,G4), DF: AC4]}, PE 4: {[(*,G1); Upstream to: PW1to4; Downstream to: ], [(*,G4); Upstream to: PW3to4; Downstream [Page 29]
Internet Draft draft-serbest-l2vpn-vpls-mcast-01.txt November, 2004 to:], [PIM Neighbors: (Router 1,PW1to4), (Router 2,Router 3,PW2to4), (Router 4,PW3to4), (Router 5,AC5)], [(*,G1), DF: PW1to4], [(*,G4), DF: PW3to4]}. - Next, assume Router 4 wants to join the multicast group (*,G1). All PEs update their states as follows: PE 1: {[(*,G1); Upstream to: AC1; Downstream to: PW1to2, PW1to3], [(*,G4); Upstream to: PW1to3; Downstream to:], [PIM Neighbors: (Router 1,AC1), (Router 2,Router 3,PW1to2), (Router 4,PW1to3), (Router 5,PW1to4)], [(*,G1), DF: AC1], [(*,G4), DF: PW1to4]}, PE 2: {[(*,G1); Upstream to: PW1to2; Downstream to: AC2], [(*,G4); Upstream to: PW2to3; Downstream to:], [PIM Neighbors: (Router 1,PW1to2), (Router 2,AC2), (Router 3,AC3), (Router 4,PW2to3), (Router 5,PW2to4)], [(*,G1), DF:PW1to2], [(*,G4), DF:PW2to3]}, PE 3: {[(*,G1); Upstream to: PW1to3; Downstream to: AC4], [(*,G4); Upstream to: AC4; Downstream to:], [PIM Neighbors: (Router 1,PW1to3), (Router 2,Router 3,PW2to3), (Router 4,AC4), (Router 5,PW3to4)], [(*,G1), DF: PW1to3], [(*,G4), DF: AC4]}, PE 4: {[(*,G1); Upstream to: PW1to4; Downstream to: ], [(*,G4); Upstream to: PW3to4; Downstream to:], [PIM Neighbors: (Router 1,PW1to4), (Router 2,Router 3,PW2to4), (Router 4,PW3to4), (Router 5,AC5)], [(*,G1), DF: PW1to4], [(*,G4), DF: PW3to4]}. - Then, assume Router 5 wants to join the multicast group (*,G4). Following the same procedures, all PEs update their states as follows: PE 1: {[(*,G1); Upstream to: AC1; Downstream to: PW1to2, PW1to3], [(*,G4); Upstream to: PW1to3; Downstream to:], [PIM Neighbors: (Router 1,AC1), (Router 2,Router 3,PW1to2), (Router 4,PW1to3), (Router 5,PW1to4)], [(*,G1), DF: AC1], [(*,G4), DF: PW1to4]}, PE 2: {[(*,G1); Upstream to: PW1to2; Downstream to: AC2], [(*,G4); Upstream to: PW2to3; Downstream to:], [PIM Neighbors: (Router 1,PW1to2), (Router 2,AC2), (Router 3,AC3), (Router 4,PW2to3), (Router 5,PW2to4)], [(*,G1), DF:PW1to2], [(*,G4), DF:PW2to3]}, PE 3: {[(*,G1); Upstream to: PW1to3; Downstream to: AC4], [(*,G4); Upstream to: AC4; Downstream to: PW3to4], [PIM Neighbors: (Router 1,PW1to3), (Router 2,Router 3,PW2to3), (Router 4,AC4), (Router 5,PW3to4)], [(*,G1), DF: PW1to3], [(*,G4), DF: AC4]}, PE 4: {[(*,G1); Upstream to: PW1to4; Downstream to: ], [(*,G4); Upstream to: PW3to4; Downstream to: AC5], [PIM Neighbors: (Router 1,PW1to4), (Router 2,Router 3,PW2to4), (Router 4,PW3to4), (Router 5,AC5)], [(*,G1), DF: PW1to4], [(*,G4), DF: PW3to4]}. 5.3.4.4 BIDIR-PIM Prune At this point, all PEs have necessary states to not send multicast traffic to sites with no members. [Page 30]
Internet Draft draft-serbest-l2vpn-vpls-mcast-01.txt November, 2004 One example of the BIDIR-PIM snooping mechanism for leaving a multicast group works as follows: - Assume Router 2 wants to leave the multicast group (*,G1) and sends a (*,G1) prune message. The prune message gets flooded in the VPLS instance. All PEs update their states as follows: PE 1: {[(*,G1); Upstream to: AC1; Downstream to: PW1to3], [(*,G4); Upstream to: PW1to3; Downstream to:], [PIM Neighbors: (Router 1,AC1), (Router 2,Router 3,PW1to2), (Router 4,PW1to3), (Router 5,PW1to4)], [(*,G1), DF: AC1], [(*,G4), DF: PW1to4]}, PE 2: {[(*,G1); Upstream to: PW1to2; Downstream to: ], [(*,G4); Upstream to: PW2to3; Downstream to:], [PIM Neighbors: (Router 1,PW1to2), (Router 2,AC2), (Router 3,AC3), (Router 4,PW2to3), (Router 5,PW2to4)], [(*,G1), DF:PW1to2], [(*,G4), DF:PW2to3]}, PE 3: {[(*,G1); Upstream to: PW1to3; Downstream to: AC4], [(*,G4); Upstream to: AC4; Downstream to: PW3to4], [PIM Neighbors: (Router 1,PW1to3), (Router 2,Router 3,PW2to3), (Router 4,AC4), (Router 5,PW3to4)], [(*,G1), DF: PW1to3], [(*,G4), DF: AC4]}, PE 4: {[(*,G1); Upstream to: PW1to4; Downstream to: ], [(*,G4); Upstream to: PW3to4; Downstream to: AC5], [PIM Neighbors: (Router 1,PW1to4), (Router 2,Router 3,PW2to4), (Router 4,PW3to4), (Router 5,AC5)], [(*,G1), DF: PW1to4], [(*,G4), DF: PW3to4]}. 5.3.4.5 Failure Scenarios Once again, failures can be easily handled in BIDIR-PIM snooping, as it employs state-refresh technique. PEs in the VPLS instance will remove entry for non-refreshing routers from their states. 5.3.5 Multicast Source Directly Connected to the VPLS Instance If there is a source in the CE network that connects directly into the VPLS instance, then multicast traffic from that source MUST be sent to all PIM routers on the VPLS instance. If there is already (S,G)/(*,G) snooping state that is formed on any PE, this will not happen per the current forwarding rules and guidelines. The (S,G)/(*,G) state may not send traffic towards all the routers. So, in order to determine if traffic needs to be flooded to all routers, a PE must be able to determine if the traffic came from a host on that LAN. There are three ways to address this problem: - The PE would have to do ARP snooping to determine if a source is directly connected. - Another option is to have configuration on all PEs to say there are CE sources that are directly connected to the VPLS instance and disallow snooping for the groups for which the source is going to send traffic. This way traffic from that source to those groups will always be flooded within the provider network. - A third option is to require that sources of CE multicast routers must appear behind a router. [Page 31]
Internet Draft draft-serbest-l2vpn-vpls-mcast-01.txt November, 2004 6 Security Considerations Security considerations provided in VPLS solution documents (i.e., [VPLS-LDP] and [VPLS-BGP) apply to this document as well. 7 References 7.1 Normative References 7.2 Informative References [VPLS-LDP] Lasserre, M, et al. "Virtual Private LAN Services over MPLS", work in progress [VPLSD-BGP] Kompella, K, et al. "Virtual Private LAN Service", work in progress [L2VPN-FR] Andersson, L, et al. "L2VPN Framework", work in progress [PMP-RSVP-TE] Aggarwal, R, et al. "Extensions to RSVP-TE for Point to Multipoint TE LSPs", work in progress [RFC1112] Deering, S., "Host Extensions for IP Multicasting", RFC 1112, August 1989. [RFC2236] Fenner, W., "Internet Group Management Protocol, Version 2", RFC 2236, November 1997. [RFC3376] Cain, B., et al. "Internet Group Management Protocol, Version 3", RFC 3376, October 2002. [MAGMA-SNOOP] Christensen, M., et al. "Considerations for IGMP and MLD Snooping Switches", work in progress [PIM-DM] Deering, S., et al. "Protocol Independent Multicast Version 2 û Dense Mode Specification", draft-ietf- pim-v2-dm-03.txt, June 1999. [RFC2362] Estrin, D, et al. "Protocol Independent Multicast- Sparse Mode (PIM-SM): Protocol Specification", RFC 2362, June 1998. [PIM-SSM] Holbrook, H., et al. "Source-Specific Multicast for IP", work in progress [BIDIR-PIM] Handley, M., et al. "Bi-directional Protocol Independent Multicast (BIDIR-PIM)", work in progress 8 Authors' Addresses Yetik Serbest SBC Labs 9505 Arboretum Blvd. Austin, TX 78759 Yetik_serbest@labs.sbc.com Ray Qiu Alcatel North America 701 East Middlefield Rd. Mountain View, CA 94043 Ray.Qiu@alcatel.com Venu Hemige [Page 32]
Internet Draft draft-serbest-l2vpn-vpls-mcast-01.txt November, 2004 Alcatel North America 701 East Middlefield Rd. Mountain View, CA 94043 Venu.hemige@alcatel.com Rob Nath Riverstone Networks 5200 Great America Parkway Santa Clara, CA 95054 Rnath@riverstonenet.com Suresh Boddapati Alcatel North America 701 East Middlefield Rd. Mountain View, CA 94043 Suresh.boddapati@alcatel.com Sunil Khandekar Alcatel North America 701 East Middlefield Rd. Mountain View, CA 94043 Sunil.khandekar@alcatel.com Vach Kompella Alcatel North America 701 East Middlefield Rd. Mountain View, CA 94043 Vach.kompella@alcatel.com Marc Lasserre Riverstone Networks Marc@riverstonenet.com 9 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. [Page 33]
Internet Draft draft-serbest-l2vpn-vpls-mcast-01.txt November, 2004 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. 10 Full copyright statement Copyright (C) The Internet Society (2004). 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. [Page 34]