Network Working Group R. Aggarwal Internet Draft Juniper Networks Expiration Date: March 2008 Y. Kamite NTT Communications L. Fang Cisco Systems, Inc September 2007 Multicast in VPLS draft-ietf-l2vpn-vpls-mcast-02.txt Status of this Memo By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or she is aware have been or will be disclosed, and any of which he or she becomes aware will be disclosed, in accordance with Section 6 of BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. Abstract This document describes a solution for overcoming a subset of the limitations of existing VPLS multicast solutions. It describes procedures for VPLS multicast that utilize multicast trees in the sevice provider (SP) network. One such multicast tree can be shared between multiple VPLS instances. Procedures by which a single multicast tree in the backbone can be used to carry traffic belonging Raggarwa, Kamite & Fang [Page 1] Internet Draft draft-ietf-l2vpn-vpls-mcast-02.txt September 2007 only to a specified set of one or more IP multicast streams from one or more VPLSs are also described. Raggarwa, Kamite & Fang [Page 2] Internet Draft draft-ietf-l2vpn-vpls-mcast-02.txt September 2007 Table of Contents 1 Specification of requirements ......................... 4 2 Contributors .......................................... 4 3 Terminology ........................................... 4 4 Introduction .......................................... 5 5 Existing Limitations of VPLS Multicast ................ 5 6 Overview .............................................. 6 6.1 Inclusive and Selective Multicast Trees ............... 6 6.2 BGP-Based VPLS Membership Auto-Discovery .............. 7 6.3 IP Multicast Group Membership Discovery ............... 7 6.4 Advertising P-Tree to VPLS / C-Multicast Binding ...... 7 6.5 Aggregation ........................................... 8 6.6 Inter-AS VPLS Multicast ............................... 8 7 VPLS Multicast/Broadcast/Unknown Unicast Data Packet Treatment 9 8 Intra-AS Inclusive Multicast Tree Auto-Discovery/Binding ..10 8.1 Originating (intra-AS) auto-discovery routes .......... 10 8.2 Receiving (intra-AS) auto-discovery routes ............ 11 9 Demultiplexing Multicast Tree Traffic ................. 12 9.1 One Multicast Tree - One VPLS Mapping ................. 13 9.1.1 One Multicast Tree - Many VPLS Mapping ................ 13 10 Establishing Multicast Trees .......................... 14 10.1 RSVP-TE P2MP LSPs ..................................... 14 10.1.1 P2MP TE LSP - VPLS Mapping ............................ 14 10.1.2 Demultiplexing C-Multicast Data Packets ............... 14 10.2 Receiver Initiated MPLS Trees ......................... 15 10.2.1 P2MP LSP - VPLS Mapping ............................... 15 10.2.2 Demultiplexing C-Multicast Data Packets ............... 16 10.3 Encapsulation of the Aggregate Inclusive and Selective Tree 16 11 Inter-AS Inclusive Multicast Tree Auto-Discovery/Binding ..16 11.1 VSIs on the ASBRs ..................................... 16 11.1.1 VPLS Inter-AS Auto-Discovery Binding .................. 16 11.2 Segmented Inter-AS Trees .............................. 17 11.3 Segmented Inter-AS Trees VPLS Inter-AS Auto-Discovery/Binding 17 11.3.1 Propagating VPLS BGP Auto-Discovery routes to other ASes - Overview 18 11.3.1.1 Propagating Intra-AS VPLS Auto-Discovery routes in EBGP ...19 11.3.1.2 Auto-Discovery Route received via EBGP ................ 20 11.3.1.3 Leaf Auto-Discovery Route received via EBGP ........... 21 11.3.1.4 Inter-AS Auto-Discovery Route received via IBGP ....... 22 12 Selective Tree Instantiation .......................... 23 12.1 Selective Tree Leaf Discovery ......................... 23 12.2 Selective Tree - C-Multicast Stream Binding Advertisement .23 12.3 Switching to Aggregate Selective Trees ................ 24 Raggarwa, Kamite & Fang [Page 3] Internet Draft draft-ietf-l2vpn-vpls-mcast-02.txt September 2007 13 BGP Extensions ........................................ 24 13.1 Inclusive Tree/Selective Tree Identifier .............. 25 14 Aggregation Methodology ............................... 26 15 Data Forwarding ....................................... 27 15.1 MPLS Tree Encapsulation ............................... 27 16 Security Considerations ............................... 28 17 IANA Considerations ................................... 28 18 Acknowledgments ....................................... 28 19 Normative References .................................. 28 20 Informative References ................................ 29 21 Author Information .................................... 29 22 Intellectual Property Statement ....................... 30 23 Full Copyright Statement .............................. 30 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. Contributors Rahul Aggarwal Yakov Rekhter Juniper Networks Yuji Kamite NTT Communications Luyuan Fang AT&T Chaitanya Kodeboniya 3. Terminology This document uses terminology described in [RFC4761] and [RFC4762]. Raggarwa, Kamite & Fang [Page 4] Internet Draft draft-ietf-l2vpn-vpls-mcast-02.txt September 2007 4. Introduction [RFC4761] and [RFC4762] describe a solution for VPLS multicast that relies on ingress replication. This solution has certain limitations for certain VPLS multicast traffic profiles. This document describes procedures for overcoming the limitations of existing VPLS multicast solutions. It describes procedures for VPLS multicast that utilize multicast trees in the sevice provider (SP) network. The procedures described in this document are applicable to both [RFC4761] and [RFC4762]. It provides mechanisms that allow a single multicast distribution tree in the backbone to carry all the multicast traffic from a specified set of one or more VPLSs. Such a tree is referred to as an "Inclusive Tree" and more specifically as an "Aggregate Inclusive Tree" when the tree is used to carry multicast traffic from more than VPLS. This document also provides procedures by which a single multicast distribution tree in the backbone can be used to carry traffic belonging only to a specified set of one or more IP multicast streams, from one or more VPLSs. Such a tree is referred to as a "Selective Tree" and more specifically as an "Aggregate Selective Tree" when the IP multicast streams belong to different VPLSs. So traffic from most multicast streams could be carried by an Inclusive Tree, while traffic from, e.g., high bandwidth streams could be carried in one of the "Selective Trees". 5. Existing Limitations of VPLS Multicast One of the limitations of existing VPLS multicast solutions described in [RFC4761] and [RFC4762] is that they rely on ingress replication. Thus the ingress PE replicates the multicast packet for each egress PE and sends it to the egress PE using a unicast tunnel. This is a reasonable model when the bandwidth of the multicast traffic is low or/and the number of replications performed on an average on each outgoing interface for a particular customer VPLS multicast packet is small. If this is not the case it is desirable to utilize multicast trees in the SP network to transmit VPLS multicast packets [MCAST-VPLS-REQ]. Note that unicast packets that are flooded to each of the egress PEs, before the ingress PE performs learning for those unicast packets, MAY still use ingress replication. Raggarwa, Kamite & Fang [Page 5] Internet Draft draft-ietf-l2vpn-vpls-mcast-02.txt September 2007 6. Overview This document describes procedures for using multicast trees in the SP network to transport VPLS multicast data packets. RSVP-TE P2MP LSPs described in [RSVP-P2MP] are an example of such multicast trees. The use of multicast trees in the SP network can be beneficial when the bandwidth of the multicast traffic is high or when it is desirable to optimize the number of copies of a multicast packet transmitted by the ingress. This comes at a cost of state in the SP network to build multicast trees and overhead to maintain this state. This document describes procedures for using multicast trees for VPLS multicast when the provider tunneling technology is either P2MP RSVP- PE or mLDP [MLDP]. The protocol architecture described herein is considered to be flexible to support other P-tunneling technologies as well. This document uses the prefix 'C' to refer to the customer control or data packets and 'P' to refer to the provider control or data packets. An IP multicast source, group tuple is abbreviated to (S, G). 6.1. Inclusive and Selective Multicast Trees Multicast trees used for VPLS can be of two types: 1. Inclusive Trees. A single multicast distribution tree in the SP network is used to carry all the multicast traffic from a specified set of one or more VPLSs. A particular multicast distribution tree can be set up to carry the traffic of a single VPLS, or to carry the traffic of multiple VPLSs. The ability to carry the traffic of more than one VPLS on the same tree is termed 'Aggregation'. The tree will include every PE that is a member of any of the VPLSs that are using the tree. This implies that a PE may receive multicast traffic for a multicast stream even if it doesn't have any receivers on the path of that stream. 2. Selective Trees. A Selective Tree is used by a PE to send IP multicast traffic for one or more multicast streams, that belong to the same or different VPLSs, to a subset of the PEs that belong to those VPLSs. Each of the PEs in the subset should be on the path to a receiver of one or more multicast streams that are mapped onto the tree. The ability to use the same tree for multicast streams that belong to different VPLSs is termed have the ability to create separate SP multicast trees for high bandwidth multicast groups. This allows traffic for these multicast groups to reach only those PE routers that have receivers in these groups. This avoids flooding other PE routers in the VPLS. Raggarwa, Kamite & Fang [Page 6] Internet Draft draft-ietf-l2vpn-vpls-mcast-02.txt September 2007 A SP can use both Inclusive Trees and Selective Trees or either of them for a given VPLS on a PE, based on local configuration. Inclusive Trees can be used for both IP and non-IP data multicast traffic, while Selective Trees can be used only for IP multicast data traffic. A variety of transport technologies may be used in the backbone. For inclusive trees, these transport technologies include point-to- multipoint LSPs created by RSVP-TE or mLDP. For selective trees, only unicast PE-PE tunnels (using MPLS or IP/GRE encapsulation) and unidirectional single-source trees are supported, and the supported tree signaling protocols are RSVP-TE, and mLDP. This document also describes the data plane encapsulations for supporting the various SP multicast transport options. 6.2. BGP-Based VPLS Membership Auto-Discovery In order to establish Inclusive multicast trees for one or more VPLSs the root of the tree must be able to discover the other PEs that have membership in one or more of these VPLSs. This document uses the BGP- based procedures described in [RFC4761] and [L2VPN-SIG] for discovering the VPLS membership of all PEs. 6.3. IP Multicast Group Membership Discovery The setup of a Selective P-tree for one or more IP multicast (S, G)s requires the ingress PE to learn the PEs that have receivers in one or more of these (S, G)s. For discovering the IP multicast group membership, procedures described in [VPLS-CTRL] should be used. Procedures in [VPLS-CTRL] can also be used with ingress replication to send traffic for an IP multicast stream to only those PEs that are on the path to receivers for that stream. 6.4. Advertising P-Tree to VPLS / C-Multicast Binding This document also describes procedures based on BGP VPLS Auto- Discovery that are used by the root of an Aggregate Tree to advertise the Inclusive or Selective tree binding and the de-multiplexing information to the leaves of the tree. A new BGP attribute called the P-Tunnel Attribute is introduced for this purpose. Once a PE decides to bind a set of VPLSes or customer multicast groups to an Inclusive Tree or a Selective Tree, it needs to announce this binding to other PEs in the network. This procedure is referred Raggarwa, Kamite & Fang [Page 7] Internet Draft draft-ietf-l2vpn-vpls-mcast-02.txt September 2007 to as Inclusive Tree or Selective Tree binding distribution and is performed using BGP. For an Inclusive Tree this discovery implies announcing the binding of all VPLSs bound to the Inclusive Tree. The inner label assigned by the ingress PE for each VPLS MUST be included, if more than one VPLS is bound to the same tree. The Inclusive Tree Identifier MUST be included. For a Selective Tree this discovery implies announcing all the specific entries bound to this tree along with the Selective Tree Identifier. The inner label assigned for each MUST be included if s from different VPLSes are bound to the same tree. The Selective Tree Identifier MUST be included. 6.5. Aggregation As described above the ability to carry the traffic of more than one VPLS on the same tree is termed 'Aggregation'. This enables the SP to place a bound on the amount of multicast tree forwarding and control plane state which the P routers must have. If each such tree supports a set of VPLSs, the state maintained by the P routers is proportional to the product of average number of VPLSes aggregated onto a tree and the average number of PEs per VPLS. Thus the state does not grow linearly with the number of VPLSes. Aggregation requires a mechanism for the egresses of the tree to demultiplex the multicast traffic received over the tree. This document describes how upstream label allocation [MPLS-UPSTREAM] by the root of the tree can be used to perform this demultiplexing. . 6.6. Inter-AS VPLS Multicast This document specifies a model where Inter-AS VPLS service can be offered without requiring a single P-multicast tree to span multiple ASes. There are two variants of this model. In the first variant, the ASBRs perform a MAC lookup, in addition to any MPLS lookups, to determine the forwarding decision on a VPLS packet. In this variant the multicast trees are confined to an AS. Hence each AS may use a different P-tunneling technology. An ASBR on receiving a VPLS packet from another ASBR is required to perform a MAC lookup to determine how to forward the packet. Thus an ASBR is required to keep a VSI for the VPLS. In the second variant, an inter-AS multicast tree, rooted at a particular PE for a particular VPLS instance, consists of a number of "segments", one per AS, which are stitched together at Autonomous System Border Routers (ASBRs). These are known as "segmented inter-AS Raggarwa, Kamite & Fang [Page 8] Internet Draft draft-ietf-l2vpn-vpls-mcast-02.txt September 2007 trees". Each segment of a segmented inter-AS tree may use a different multicast transport technology. In this variant, an ASBR is not required to keep a a VSI for the VPLS and is not required to perform a MAC lookup in order to forward the VPLS packet. 7. VPLS Multicast/Broadcast/Unknown Unicast Data Packet Treatment If the destination MAC address of a VPLS packet received by a PE from a VPLS site is a multicast adddress, a multicast tree SHOULD be used to transport the packet, if possible. If the packet is an IP multicast packet and a Selective tree exists for that multicast stream, the Selective tree SHOULD be used. Else if an Inclusive tree exists for the VPLS, it SHOULD be used. If the destination MAC address of a VPLS packet is a broadcast address, it is flooded. If Inclusive tree is already established, PE SHOULD flood over it. If Inclusive Tree cannot be used for some reason, PE MUST flood over multiple PWs, based on [RFC4761] or [RFC4762]. If the destination MAC address of a packet is a unicast address and it has not been learned, the packet MUST be sent to all PEs in the VPLS. Inclusive multicast trees SHOULD be used for sending unknown unicast MAC packets to all PEs. When this is the case the receiving PEs MUST support the ability to perform MAC address learning for packets received on a multicast tree. In order to perform such learning, the receiver PE MUST be able to determine the sender PE when a VPLS packet is received on a multicast tree. When a receiver PE receives a VPLS packet with a source MAC address, that has not yet been learned, on a multicast tree, the receiver PE determines the PW to the sender PE. The receiver PE then creates forwarding state in the VPLS instance with a destination MAC address being the same as the source MAC address being learned, and the PW being the PW to the sender PE. It should be noted that when a sender PE that is sending packets destined to an unknown unicast MAC address over a multicast tree learns the PW to use for forwarding packets destined to this unicast MAC address, it might immediately switch to transport such packets over this particular PW. Since the packets were initially being forwarded using a multicast tree, this could lead to packet reordering. This contraint should be taken into consideration if unknown unicast frames are forwarded using a Inclusive Tree, instead of multiple PWs based on [RFC4761] or [RFC4762]. An implementation MUST support the ability to transport unknown unicast traffic over Inclusive multicast trees. Further an Raggarwa, Kamite & Fang [Page 9] Internet Draft draft-ietf-l2vpn-vpls-mcast-02.txt September 2007 implementation MUST support the ability to perform MAC address learning for packets received on a multicast tree. 8. Intra-AS Inclusive Multicast Tree Auto-Discovery/Binding This section specifies procedures for the intra-AS auto-discovery (AD) of VPLS membership and the distribution of information used to instantiate P-Multicast Tunnels. VPLS auto-discovery/binding consists of two components: intra-AS and inter-AS. The former provides VPLS auto-discovery/binding within a single AS. The latter provides VPLS auto-discovery/binding across multiple ASes. Inter-AS auto-discovery/binding is described in section 11. VPLS auto-discovery using BGP as described in [RFC4761, L2VPN-SIG] enables a PE to learn the VPLS membership of other PEs. A PE that belongs to a particular VPLS announces a BGP Network Layer Reachability Information (NLRI) that identifies the Virtual Switch Instance (VSI). This NLRI is constructed from the tuple. The NLRI defined in [RFC4761] comprises the tuple and label blocks for PW signaling. The VE-ID in this case is a two octet number. While the NLRI defined in [L2VPN-SIG] comprises only the where the VE-ID is a four octet number. The procedures for constructing Inclusive intra-AS and inter-AS trees as specified in this document require the BGP Auto-Discovery NLRI to carry only the . Hence these procedures can be used for both BGP-VPLS and LDP-VPLS with BGP Auto-Discovery. 8.1. Originating (intra-AS) auto-discovery routes To participate in the VPLS auto-discovery/binding a PE router that has a given VSI of a given VPLS originates an auto-discovery route and advertises this route in IBGP. The route is constructed as described in [RFC4761] and [L2VPN-SIG]. The route carries a single L2VPN NLRI with the RD set to the RD of the VSI, and the VE-ID set to the VE-ID of the VSI. If a P-Multicast tree is used to instantiate the provider tunnel for VPLS multicast on the PE, and either (a) this tree exists at the time of discovery, or (b) the PE doesn't need to know the leaves of the tree before hand in order to advertise the P-Multicast tree identifier, then the advertising PE SHOULD advertise the type and the Raggarwa, Kamite & Fang [Page 10] Internet Draft draft-ietf-l2vpn-vpls-mcast-02.txt September 2007 identity of the P-Multicast tree in a new BGP attribute called the the P-Tunnel attribute. This attribute is described in section 13.1. If a P-Multicast tree is used to instantiate the provider tunnel for VPLS multicast on the PE, and in order to advertise the P-Multicast tree identifier the advertising PE needs to know the leaves of the tree beforehand, then the PE obtains this information from the intra- AS auto-discovery routes received from other PEs. Once the PE obtains the information about the leaves (this information is obtained from the auto-discovery routes received by the PE), the PE then advertises the binding of the tree to the VPLS using the same route as the one used for the auto-discovery, with the addition of carrying in the route the P-Tunnel attribute that contains the type and the identity of the P-Multicast tree. If at some later point a new PE advertises participation in the same VPLS, the initial binding P-Tunnel binding information SHOULD NOT change (though the leaves of the corresponding P-Multicast tree may change). A PE that uses a P-Multicast tree to instantiate the provider tunnel MAY aggregate two or more VPLSs present on the PE onto the same tree. If the PE already advertises intra-AS auto-discovery routes for these VPLSs, then aggregation requires the PE to re-advertise these routes. The re-advertised routes MUST be the same as the original ones, except for the P-Tunnel attribute. If the PE has not previously advertised intra-AS auto-discovery routes for these VPLSs, then the aggregation requires the PE to advertise (new) intra-AS auto- discovery routes for these VPLSs. The P-Tunnel attribute in the newly advertised/re-advertised routes MUST carry the identity of the P-Multicast tree that aggregates the VPLSs, as well as an MPLS upstream assigned label [MPLS-UPSTREAM]. Each re-advertised route MUST have a distinct label. Discovery of PE capabilities in terms of what tunnels types they support is outside the scope of this document. Within a given AS PEs participating in a VPLS are expected to advertise tunnel bindings whose tunnel types are supported by all other PEs that are participating in this VPLS and are part of the same AS. 8.2. Receiving (intra-AS) auto-discovery routes When a PE receives a BGP Update message that carries an auto- discovery route such that (a) the route was originated by some other PE within the same AS as the local PE, (b) at least one of the Route Targets of the route matches one of the import Route Targets configured for a particular VSI on the local PE, (c) the BGP route selection determines that this is the best route with respect to the NLRI carried by the route, and (d) the route carries the P-Tunnel Raggarwa, Kamite & Fang [Page 11] Internet Draft draft-ietf-l2vpn-vpls-mcast-02.txt September 2007 attribute, the PE performs the following. If the route carries the P-Tunnel attribute then: + If the Tunnel Type in the P-Tunnel attribute is set to LDP P2MP LSP, the PE SHOULD join the P-Multicast tree whose identity is carried in the P-Tunnel Attribute. + If the Tunnel Type in the P-Tunnel attribute is set to RSVP-TE P2MP LSP, the receiving PE has to establish the appropriate state to properly handle the traffic received over that LSP. The PE that originated the route MUST establish an RSVP-TE P2MP LSP with the local PE as a leaf. This LSP MAY have been established before the local PE receives the route. + If the P-Tunnel attribute does not carry a label, then all packets that are received on the P-Multicast tree, as identified by the P-Tunnel attribute, are forwarded using the VSI that has at least one of its import Route Targets that matches one of the Route Targets of the received auto-discovery route. + If the P-Tunnel attribute has the Tunnel Type set to LDP P2MP LSP or RSVP-TE P2MP LSP, and the attribute also carries an MPLS label, then the egress PE MUST treat this as an upstream assigned label, and all packets that are received on the P-Multicast tree, as identified by the P-Tunnel attribute, with that upstream label are forwarded using the VSI that has at least one of its import Route Target that matches one of the Route Targets of the received auto-discovery route. Irrespective of whether the route carries the PMSI Tunnel attribute, if the local PE uses RSVP-TE P2MP LSP for sending (multicast) traffic from the VRF to the sites attached to other PEs, then the local PE uses the Originating Router's IP address information carried in the route to add the PE that originated the route as a leaf node to the LSP. 9. Demultiplexing Multicast Tree Traffic Demultiplexing received VPLS traffic requires the receiving PE to determine the VPLS instance the packet belongs to. The egress PE can then perform a VPLS lookup to further forward the packet. Raggarwa, Kamite & Fang [Page 12] Internet Draft draft-ietf-l2vpn-vpls-mcast-02.txt September 2007 9.1. One Multicast Tree - One VPLS Mapping When a multicast tree is mapped to only one VPLS, determining the tree on which the packet is received is sufficient to determine the VPLS instance on which the packet is received. The tree is determined based on the tree encapsulation. If MPLS encapsulation is used, eg: RSVP-TE P2MP LSPs, the outer MPLS label is used to determine the tree. Penultimate-hop-popping MUST be disabled on the RSVP-TE P2MP LSP. 9.1.1. One Multicast Tree - Many VPLS Mapping As traffic belonging to multiple VPLSs can be carried over the same tree, there is a need to identify the VPLS the packet belongs to. This is done by using an inner label that corresponds to the VPLS for which the packet is intended. The ingress PE uses this label as the inner label while encapsulating a customer multicast data packet. Each of the egress PEs must be able to associate this inner label with the same VPLS and use it to demultimplex the traffic received over the Aggregate Inclusive Tree or the Aggregate Selective Tree. If downstream label assignment were used this would require all the egress PEs in the VPLS to agree on a common label for the VPLS. This document requires the use of upstream label assignment by the ingress PE [MPLS-UPSTREAM]. Hence the inner label is assigned by the ingress PE. Each egress PE maintains a separate label space for every other PE that is the root of an Aggregate Tree. The egress PEs create a forwarding entry for the inner VPLS label, assigned by the ingress PE, in this label space. When the egress PE receives a packet over an Aggregate Tree, the outer encapsulation [in the case of MPLS P2MP LSPs, the outer MPLS label] specifies the label space to perform the inner label lookup. The same label space may be used for all P- multicast trees rooted at the same ingress PE, or an implementation may decide to use a separate label space for every P-multicast tree [MPLS-UPSTREAM]. If the tree uses MPLS encapsulation the outer MPLS label and the incoming interface provides the label space of the label beneath it. This assumes that penultimate-hop-popping is disabled. An example of this is RSVP-TE P2MP LSPs. The outer label and incoming interface effectively identifies the Tree [MPLS-UPSTREAM, MPLS-MCAST]. The ingress PE informs the egress PEs about the inner label as part of the tree binding procedures described in section 12. Raggarwa, Kamite & Fang [Page 13] Internet Draft draft-ietf-l2vpn-vpls-mcast-02.txt September 2007 10. Establishing Multicast Trees This document does not place any fundamental restrictions on the multicast technology used to setup P-multicast trees. However specific procedures are specified currently only for RSVP-TE P2MP LSPs and LDP P2MP LSPs. A P-multicast tree can be either a source tree or a shared tree. A source tree is used to carry traffic only for the VPLSs that exist locally on the root of the tree i.e. for which the root has local CEs. A shared tree on the other hand can be used to carry traffic belonging to VPLSs that exist on other PEs as well. The shared tree root participates in VPLS auto-discovery. Each of the PEs transport the VPLS traffic to the shared tree root using ingress replication. The shared root splices the traffic onto the shared tree. 10.1. RSVP-TE P2MP LSPs This section describes procedures that are specific to the usage of RSVP-TE P2MP LSPs for instantiating a multicast tree. The RSVP-TE P2MP LSP can be either a source tree or a shared tree. Procedures in [RSVP-TE-P2MP] are used to signal the P2MP LSP. The LSP is signaled after the root of the P2MP LSP discovers the leaves. The egress PEs are discovered using the procedures described in section 9. Aggregation as described in this document is supported. 10.1.1. P2MP TE LSP - VPLS Mapping P2MP TE LSP to VPLS mapping is learned at the egress PEs using BGP based advertisements of the P2MP TE LSP - VPLS mapping. They require that the root of the tree include the P2MP TE LSP identifier as the tunnel identifier in the BGP advertisements. This identifier contains the following information elements: - The type of the tunnel is set to RSVP-TE P2MP LSP - RSVP-TE P2MP LSP's SESSION Object This Tunnel Identifier is described in section 13.1. 10.1.2. Demultiplexing C-Multicast Data Packets Demultiplexing the C-multicast data packets at the egress PE requires that the PE must be able to determine the P2MP TE LSP that the packets are received on. The egress PE needs to determine the P2MP LSP to determine the VPLS that the packet belongs to, as described in section 10. To achieve this the LSP must be signaled with Raggarwa, Kamite & Fang [Page 14] Internet Draft draft-ietf-l2vpn-vpls-mcast-02.txt September 2007 penultimate-hop-popping (PHP) off. This is because the egress PE needs to rely on the MPLS label, that it advertises to its upstream neighbor, to determine the P2MP LSP that a C-multicast data packet is received on. The egress PE relies on receiving the P-Tunnel Attribute in BGP to determine the VPLS instance to P2MP TE LSP mapping. Once the egress PE receives this mapping: + If the egress PE already has RSVP-TE state for the P2MP TE LSP, it MUST begin to assign a MPLS label from the non-reserved label range, for the P2MP TE LSP and signal this to the previous hop of the P2MP TE LSP. Further it MUST create forwarding state to forward packets received on the P2MP LSP. + If the egress PE does not have RSVP-TE state for the P2MP TE LSP, it MUST retain this mapping. Subsequently when the egress PE receives the RSVP-TE P2MP signaling message, it creates the RSVP- TE P2MP LSP state. It MUST then assign a MPLS label from the non-reserved label range, for the P2MP TE LSP, and signal this to the previous hop of the P2MP TE LSP. 10.2. Receiver Initiated MPLS Trees Receiver initiated MPLS trees can also be used. An example of such trees are LDP setup P2MP MPLS Trees [MLDP]. The LDP P2MP LSP can be either a source tree or a shared tree. Procedures in [MLDP] are used to signal the LSP. The LSP is signaled once the leaves receive the LDP FEC for the tree from the root. The egress PEs are discovered using the procedures described in section 9. Aggregation as described in this document is supported. 10.2.1. P2MP LSP - VPLS Mapping P2MP LSP to VPLS mapping is learned at the egress PEs using BGP based advertisements of the P2MP LSP - VPLS mapping. They require that the root of the tree include the P2MP LSP identifier as the tunnel identifier in the BGP advertisements. This identifier contains the following information elements: - The type of the tunnel is set to LDP P2MP LSP - LDP P2MP FEC which includes an identifier generated by the root. Each egress PE "joins" the P2MP MPLS tree by sending LDP label Raggarwa, Kamite & Fang [Page 15] Internet Draft draft-ietf-l2vpn-vpls-mcast-02.txt September 2007 mapping messages for the LDP P2MP FEC, that was learned in the BGP advertisement, using procedures described in [MLDP]. 10.2.2. Demultiplexing C-Multicast Data Packets This follows the same procedures described above for RSVP-TE P2MP LSPs. 10.3. Encapsulation of the Aggregate Inclusive and Selective Tree An Aggregate Inclusive Tree or an Aggregate Selective Tree MUST use a MPLS encapsulation. The protocol type in the data link header is as described in [MPLS-MCAST]. 11. Inter-AS Inclusive Multicast Tree Auto-Discovery/Binding This document specifies a solution where Inter-AS VPLS service can be offered without requiring a single P-multicast tree to span multiple ASes. This allows individual ASes to potentially use different P- tunneling technologies. There are two variants of this solution. 11.1. VSIs on the ASBRs In this variant, the ASBRs perform a MAC lookup, in addition to any MPLS lookups, to determine the forwarding decision on a VPLS packet. In this variant the multicast trees are confined to an AS. An ASBR on receiving a VPLS packet from another ASBR is required to perform a MAC lookup to determine how to forward the packet. Thus an ASBR is required to keep a VSI for the VPLS and is configured with its own VE ID for the VPLS. This is equivalent to inter-AS option A described in [RFC4364]. 11.1.1. VPLS Inter-AS Auto-Discovery Binding In this variant the BGP AD routes generated by PEs in an AS are not propagated outside the AS. The only AD routes that are propagated outside the AS are the ones originated by ASBRs. The ASBR - ASBR inter-connect may be a MPLS PW or a layer-2 interface that maps to a VPLS instance at the ASBR. If it is a MPLS PW, this MPLS PW is signaled using the procedures defined in [RFC4361] or [RFC4362], and connects the VSIs on the ASBRs The multicast trees for a VPLS are confined to each AS and the VPLS Raggarwa, Kamite & Fang [Page 16] Internet Draft draft-ietf-l2vpn-vpls-mcast-02.txt September 2007 auto-discovery/binding follows the intra-AS procedures described in section 8. 11.2. Segmented Inter-AS Trees In the second variant, an inter-AS multicast tree, rooted at a particular PE for a particular VPLS instance, consists of a number of "segments", one per AS, which are stitched together at Autonomous System Border Routers (ASBRs). These are known as "segmented inter-AS trees". Each segment of a segmented inter-AS tree may use a different multicast transport technology. In this variant, an ASBR is not required to keep a a VSI for the VPLS and is not required to perform a MAC lookup in order to forward the VPLS packet. This implies that an ASBR is not required to be configured with a VE ID for the VPLS. The construction of segmented Inter-AS trees requires the BGP-VPLS Auto-Discovery NLRI described in [RFC4361, RFC4362]. A BGP-VPLS AD route for a tuple advertised outside the AS, to which the originating PE belongs, will be referred to as an inter-AS auto- discovery route. In addition to this segmented inter-AS trees require support for the P-Tunnel Attribute described in section 13.1. They also require additional procedures in BGP to signal leaf AD routes between Autonomous System Border Routers (ASBRs) as explained in subsequent sections. 11.3. Segmented Inter-AS Trees VPLS Inter-AS Auto-Discovery/Binding This section specifies the procedures for inter-AS VPLS Auto- Discovery/binding for segmented inter-AS trees. An ASBR must be configured to support a particular VPLS as follows: + An ASBR MUST be be configured with a set of (import) Route Targets (RTs) that specifies the set of VPLSes supported by the ASBR. These Route Targets control acceptance of BGP VPLS auto- discovery routes by the ASBR. + The ASBR MUST be configured with the tunnel types for the intra- AS segments of the VPLSes supported by the ASBR, as well as (depending on the tunnel type) the information needed to create the P-Tunnel attribute for these tunnel types. Raggarwa, Kamite & Fang [Page 17] Internet Draft draft-ietf-l2vpn-vpls-mcast-02.txt September 2007 If an ASBR is configured to support a particular VPLS, the ASBR MUST participate in the intra-AS VPLS auto-discovery/binding procedures for that VPLS within the ASBR's own AS, as defined in this document. Moreover, in addition to the above the ASBR performs procedures specified in the next section. 11.3.1. Propagating VPLS BGP Auto-Discovery routes to other ASes - Overview An auto-discovery route for a given VPLS, originated by an ASBR within a given AS, is propagated via BGP to other ASes. The precise rules for distributing and processing the inter-AS auto-discovery routes are given in subsequent sections. Suppose that an ASBR A receives and installs an auto-discovery route for VPLS "X" and VE ID "V" that originated at a particular PE, PE1. The BGP next hop of that received route becomes A's "upstream neighbor" on a multicast distribution tree for (X, V) that is rooted at PE1. When the auto-discovery routes have been distributed to all the necessary ASes, they define a "reverse path" from any AS that supports VPLS X and VE ID V back to PE1. For instance, if AS2 supports VPLS X, then there will be a reverse path for VPLS X and VE ID V from AS2 to AS1. This path is a sequence of ASBRs, the first of which is in AS2, and the last of which is in AS1. Each ASBR in the sequence is the BGP next hop of the previous ASBR in the sequence on the given auto-discovery route. This reverse path information can be used to construct a unidirectional multicast distribution tree for VPLS X and VE ID V, containing all the ASes that support X, and having PE1 at the root. We call such a tree an "inter-AS tree". Multicast data originating in VPLS sites for VPLS X connected to PE1 will travel downstream along the tree which is rooted at PE1. The path along an inter-AS tree is a sequence of ASBRs; it is still necessary to specify how the multicast data gets from a given ASBR to the set of ASBRs which are immediately downstream of the given ASBR along the tree. This is done by creating "segments": ASBRs in adjacent ASes will be connected by inter-AS segments, ASBRs in the same AS will be connected by "intra-AS segments". For a given inter-AS tree, there MUST be only one ASBR that accepts traffic into a given AS. Further there MUST be only one ASBR that sends traffic from a particular AS on the tree to another adjacent AS. Raggarwa, Kamite & Fang [Page 18] Internet Draft draft-ietf-l2vpn-vpls-mcast-02.txt September 2007 An ASBR initiates creation of an intra-AS segment when the ASBR receives an auto-discovery route from an EBGP neighbor. Creation of the segment is completed as a result of distributing via IBGP this route within the ASBR's own AS. For a given inter-AS tunnel each of its intra-AS segments could be constructed by its own independent mechanism. Moreover, by using upstream assigned labels within a given AS multiple intra-AS segments of different inter-AS tunnels of either the same or different VPLSs may share the same P-Multicast tree. If the P-Multicast tree instantiating a particular segment of an inter-AS tunnel is created by a multicast control protocol that uses receiver-initiated joins (e.g, mLDP), and this P-Multicast tree does not aggregate multiple segments, then all the information needed to create that segment will be present in the inter-AS auto-discovery routes received by the ASBR from the neighboring ASBR. But if the P- Multicast tree instantiating the segment is created by a protocol that does not use receiver-initiated joins (e.g., RSVP-TE, ingress unicast replication), or if this P-Multicast tree aggregates multiple segments (irrespective of the multicast control protocol used to create the tree), then the ASBR needs to learn the leaves of the segment. These leaves are learned from AD routes received from other PEs in the AS, for the same VPLS (i.e. same VE-ID). The following sections specify procedures for propagation of auto- discovery routes across ASes in order to construct inter-AS segmented trees. 11.3.1.1. Propagating Intra-AS VPLS Auto-Discovery routes in EBGP For a given VPLS configured on an ASBR when the ASBR determines (using the intra-AS auto-discovery procedures) that one or more PEs of its own AS has (directly) connected site(s) of the VPLS, the ASBR: originates an BGP VPLS auto-discovery route and advertises it in EBGP for each of the BGP VPLS auto-discovery routes received by the ASBR from the PEs in its own AS. Each of these routes is constructed as follows: + The route carries a single BGP VPLS AD NLRI with the RD and VE ID being the same as the received NLRI. + The Next Hop field of the MP_REACH_NLRI attribute is set to a routable IP address of the ASBR. Raggarwa, Kamite & Fang [Page 19] Internet Draft draft-ietf-l2vpn-vpls-mcast-02.txt September 2007 + The route carries the P-Tunnel attribute with the Tunnel Type set to Ingress Replication; the attribute carries no MPLS labels. + The route MUST carry the export Route Target used by the VPLS. 11.3.1.2. Auto-Discovery Route received via EBGP When an ASBR receives from one of its EBGP neighbors a BGP Update message that carries an auto-discovery route, if (a) at least one of the Route Targets carried in the message matches one of the import Route Targets configured on the ASBR, and (b) the ASBR determines that the received route is the best route to the destination carried in the NLRI of the route, the ASBR re-advertises this auto-discovery route to other PEs and ASBRs within its own AS. The best route selection procedures MUST ensure that for the same destination, all ASBRs pick the same route as the best route. This ensures that if multiple ASBRs receive the same inter-AS AD route from their EBGP neighbors, only one of these ASBRs propagates this route in IBGP. When re-advertising an inter-AS auto-discovery route the ASBR MUST set the Next Hop field of the MP_REACH_NLRI attribute to a routable IP address of the ASBR. Depending on the type of a P-Multicast tree used to instantiate the intra-AS segment of the inter-AS tunnel, the P-Tunnel attribute of the re-advertised inter-AS auto-discovery route is constructed as follows: + If the ASBR uses ingress replication to instantiate the intra-AS segment of the inter-AS tunnel, the re-advertised route SHOULD carry the P-Tunnel attribute with the Tunnel Type set to Ingress Replication, but no MPLS labels. + If the ASBR uses a P-Multicast tree to instantiate the intra-AS segment of the inter-AS tunnel, the PMSI Tunnel attribute MUST contain the identity of the tree that is used to instantiate the segment (note that the ASBR could create the identity of the tree prior to the actual instantiation of the segment). If in order to instantiate the segment the ASBR needs to know the leaves of the tree, then the ASBR obtains this information from the auto- discovery routes received from other PEs/ASBRs in ASBR's own AS. + An ASBR that uses a P-Multicast tree to instantiate the intra-AS segment of the inter-AS tunnel MAY aggregate two or more MVPNs present on the ASBR onto the same tree. If the ASBR already advertises inter-AS auto-discovery routes for these MVPNs, then aggregation requires the ASBR to re-advertise these routes. The Raggarwa, Kamite & Fang [Page 20] Internet Draft draft-ietf-l2vpn-vpls-mcast-02.txt September 2007 re-advertised routes MUST be the same as the original ones, except for the PMSI Tunnel attribute. If the ASBR has not previously advertised inter-AS auto-discovery routes for these MVPNs, then the aggregation requires the ASBR to advertise (new) inter-AS auto-discovery routes for these MVPN. The PMSI Tunnel attribute in the newly advertised/re-advertised routes MUST carry the identity of the P-Multicast tree that aggregates the MVPNs, as well as an MPLS upstream assigned label [MPLS-UPSTREAM]. Each re-advertised route MUST have a distinct label. In addition the ASBR MUST send to the EBGP neighbor, from whom it receives the inter-AS auto-discovery route, a BGP Update message that carries a "leaf auto-discovery route". The exact encoding of this route will be described in the next revision. This route contains the following information elements: + The route carries a single NLRI with the Route Key field set to the tuple of the BGP VPLS Auto-Discovery NLRI of the inter-AS auto-discovery route received from that neighbor. The NLRI also carries the IP address of the ASBR (this MUST be a routable IP address). + The leaf auto-discovery route MUST include the P-Tunnel attribute with the Tunnel Type set to Ingress Replication, and the Tunnel Identifier set to a routable address of the advertising router. The P-Tunnel attribute MUST carry a downstream assigned MPLS label that is used to demultiplex the VPLS traffic received over a unicast tunnel by the advertising router. + The Next Hop field of the MP_REACH_NLRI attribute of the route SHOULD be set to the same IP address as the one carried in the Originating Router's IP Address field of the route. + To constrain the distribution scope of this route the route MUST carry the NO_ADVERTISE BGP community ([RFC1997]). + The Route Targets associated with the VPLS MUST be included in the route. 11.3.1.3. Leaf Auto-Discovery Route received via EBGP When an ASBR receives via EBGP a leaf auto-discovery route, the ASBR accepts the route only if if (a) at least one of the Route Targets carried in the message matches one of the import Route Targets configured on the ASBR, and (b) the ASBR determines that the received route is the best route to the destination carried in the NLRI of the Raggarwa, Kamite & Fang [Page 21] Internet Draft draft-ietf-l2vpn-vpls-mcast-02.txt September 2007 route. If the ASBR accepts the leaf auto-discovery route, the ASBR finds an auto-discovery route whose BGP-VPLS AD NLRI has the same value as the field of the the leaf auto-discovery route. The MPLS label carried in the P-Tunnel attribute of the leaf auto- discovery route is used to stitch a one hop ASBR-ASBR LSP to the tail of the intra-AS tunnel segment associated with the found auto- discovery route. 11.3.1.4. Inter-AS Auto-Discovery Route received via IBGP In the context of this section we use the term "PE/ASBR router" to denote either a PE or an ASBR router. Note that a given inter-AS auto-discovery route is advertised within a given AS by only one ASBR as described above. When a PE/ASBR router receives from one of its IBGP neighbors a BGP Update message that carries an inter-AS auto-discovery route, if (a) at least one of the Route Targets carried in the message matches one of the import Route Targets configured on the PE/ASBR, and (b) the PE/ASBR determines that the received route is the best route to the destination carried in the NLRI of the route, the PE/ASBR performs the following operations. If the router is an ASBR then the ASBR propagates the route to its EBGP neighbors. When propagating the route to the EBGP neighbors the ASBR MUST set the Next Hop field of the MP_REACH_NLRI attribute to a routable IP address of the ASBR. If the received inter-AS auto-discovery route carries the P-Tunnel attribute with the Tunnel Type set to LDP P2MP LSP, the PE/ASBR SHOULD join the P-Multicast tree whose identity is carried in the P- Tunnel Attribute. If the received inter-AS auto-discovery route carries the P-Tunnel attribute with the Tunnel Identifier set to RSVP-TE P2MP LSP, then the ASBR that originated the route MUST establish an RSVP-TE P2MP LSP with the local PE/ASBRas a leaf. This LSP MAY have been established before the local PE/ASBR receives the route, or MAY be established after the local PE receives the route. If the received inter-AS auto-discovery route carries the P-Tunnel attribute with the Tunnel Type set to LDP P2MP LSP, or RSVP-TE P2MP LSP, but the attribute does not carry a label, then the P-Multicast Raggarwa, Kamite & Fang [Page 22] Internet Draft draft-ietf-l2vpn-vpls-mcast-02.txt September 2007 tree, as identified by the P-Tunnel Attribute, is an intra-AS LSP segment that is part of the inter-AS Tunnel for the advertised by the inter-AS auto-discovery route and rooted at the PE that originated the auto-discovery route. If the P-Tunnel attribute carries a (upstream assigned) label, then a combination of this tree and the label identifies the intra-AS segment. If the received router is an ASBR, this intra-AS segment may further be stitched to ASBR- ASBR inter-AS segment of the inter-AS tunnel. If the PE/ASBR has local receivers in the VPLS, packets received over the intra-AS segment must be forwarded to the local receivers using the local VSI. 12. Selective Tree Instantiation This section describes the procedures for instantiating selective trees. 12.1. Selective Tree Leaf Discovery Constructing a selective tree for a given (C-S, C-G) requires the ingress PE to learn the egress PEs that have receivers in the (C-S, C-G). Procedures for learning this information are described in [VPLS-CTRL]. 12.2. Selective Tree - C-Multicast Stream Binding Advertisement The root of an Aggregate Selective Tree maps one or more entries to the tree. These entries are advertised in BGP along with the the Selective Tree identifier to which these entries are mapped. The following information is required in BGP to advertise the entries that are mapped to the Selective Tree. The exact encoding of this information will be specified in the next revision: 1. The RD configured for the VPLS instance. This is required to uniquely identify the as the addresses could overlap between different VPLS instances. 2. The inner label allocated by the Selective Tree root for the . The usage of this label is described in section 9. 3. The C-Source address. This address can be a prefix in order to allow a range of C-Source addresses to be mapped to the Selective Tree. 4. The C-Group address. This address can be a range in order to allow a range of C-Group addresses to be mapped to the Selective Raggarwa, Kamite & Fang [Page 23] Internet Draft draft-ietf-l2vpn-vpls-mcast-02.txt September 2007 Tree. When a PE distributes this information via BGP, it must include the following: 1. An identifier of the Selective Tree using the P-Tunnel Attribute. 2. Route Target Extended Communities attribute. This is used as described in section 8. 12.3. Switching to Aggregate Selective Trees Selective Trees provide a PE the ability to create separate P- multicast trees for certain entires. The source PE, that originates the Selective Tree, and the egress PEs, MUST to switch to the Selective Tree for the entries that are mapped to it. Once a source PE decides to setup an Selective Tree, it announces the mapping of the entries that are mapped on the tree to the other PEs using BGP. Depending on the P-multicast technology used, this announcement may be done before or after setting up the Selective Tree. After the egress PEs receive the announcement they setup their forwarding path to receive traffic on the Selective Tree if they have one or more receivers interested in the entries mapped to the tree. This implies setting up the demultiplexing forwarding entries based on the inner label as described earlier. The egress PEs may perform this switch to the Selective Tree once the advertisement from the ingress PE is received or wait for a preconfigured timer to do so. A source PE uses the following approach to decide when to start transmitting data on the Selective tree. A certain pre-configured delay after advertising the entries mapped to an Selective Tree, the source PE begins to send traffic on the Selective Tree. At this point it stops to send traffic for the entries, that are mapped on the Selective Tree, on the Inclusive Tree. This traffic is instead transmitted on the Selective Tree. 13. BGP Extensions This section describes the encoding of the BGP extensions required by this document. Raggarwa, Kamite & Fang [Page 24] Internet Draft draft-ietf-l2vpn-vpls-mcast-02.txt September 2007 13.1. Inclusive Tree/Selective Tree Identifier Inclusive Tree and Selective Tree advertisements carry the Tree identifier. This document defines and uses a new BGP attribute, called P-Tunnel Attribute. This is an optional transitive BGP attribute. The format of this attribute is defined as follows: +---------------------------------+ | Flags (1 octet) | +---------------------------------+ | Tunnel Type (1 octets) | +---------------------------------+ | MPLS Label (3 octets) | +---------------------------------+ | Tunnel Identifier (variable) | +---------------------------------+ The Flags field has the following format: 0 1 2 3 4 5 6 7 +-+-+-+-+-+-+-+-+ | reserved |L| +-+-+-+-+-+-+-+-+ This document defines the following flags: + Leaf Information Required (L) The Tunnel Type identifies the type of the tunneling technology used to establish the P-tunnel. The type determines the syntax and semantics of the Tunnel Identifier field. This document defines the following Tunnel Types: + 1 - RSVP-TE P2MP LSP + 2 - LDP P2MP LSP + 6 - Ingress Replication If the MPLS Label field is non-zero, then it contains an MPLS label encoded as 3 octets, where the high-order 20 bits contain the label value. Absence of MPLS Label is indicated by setting the MPLS Label field to zero. When the type is set to RSVP-TE P2MP LSP, the Tunnel Identifier contains the RSVP-TE P2MP LSP's SESSION Object. Raggarwa, Kamite & Fang [Page 25] Internet Draft draft-ietf-l2vpn-vpls-mcast-02.txt September 2007 When the type is set to LDP P2MP LSP, the Tunnel Identifier is . When the type is set to Ingress Replication the Tunnel Identifier carries the unicast tunnel endpoint. 14. Aggregation Methodology In general the herustics used to decide which VPLS instances or entries to aggregate is implementation dependent. It is also conceivable that offline tools can be used for this purpose. This section discusses some tradeoffs with respect to aggregation. The "congruency" of aggregation is defined by the amount of overlap in the leaves of the client trees that are aggregated on a SP tree. For Aggregate Inclusive Trees the congruency depends on the overlap in the membership of the VPLSs that are aggregated on the Aggregate Inclusive Tree. If there is complete overlap aggregation is perfectly congruent. As the overlap between the VPLSs that are aggregated reduces, the congruency reduces. If aggregation is done such that it is not perfectly congruent a PE may receive traffic for VPLSs to which it doesn't belong. As the amount of multicast traffic in these unwanted VPLSs increases aggregation becomes less optimal with respect to delivered traffic. Hence there is a tradeoff between reducing state and delivering unwanted traffic. An implementation should provide knobs to control the congruency of aggregation. This will allow a SP to deploy aggregation depending on the VPLS membership and traffic profiles in its network. If different PEs or shared roots' are setting up Aggregate Inclusive Trees this will also allow a SP to engineer the maximum amount of unwanted VPLSs that a particular PE may receive traffic for. The state/bandwidth optimality trade-off can be further improved by having a versatile many-to-many association between client trees and provider trees. Thus a VPLS can be mapped to multiple Aggregate Trees. The mechanisms for achieving this are for further study. Also it may be possible to use both ingress replication and an Aggregate Tree for a particular VPLS. Mechanisms for achieving this are also for further study. Raggarwa, Kamite & Fang [Page 26] Internet Draft draft-ietf-l2vpn-vpls-mcast-02.txt September 2007 15. Data Forwarding 15.1. MPLS Tree Encapsulation The following diagram shows the progression of the VPLS IP multicast packet as it enters and leaves the SP network when MPLS trees are being used for multiple VPLS instances. RSVP-TE P2MP LSPs are examples of such trees. Packets received Packets in transit Packets forwarded at ingress PE in the service by egress PEs provider network +---------------+ |MPLS Tree Label| +---------------+ | VPLS Label | ++=============++ ++=============++ ++=============++ ||C-Ether Hdr || || C-Ether Hdr || || C-Ether Hdr || ++=============++ >>>>> ++=============++ >>>>> ++=============++ || C-IP Header || || C-IP Header || || C-IP Header || ++=============++ >>>>> ++=============++ >>>>> ++=============++ || C-Payload || || C-Payload || || C-Payload || ++=============++ ++=============++ ++=============++ The receiver PE does a lookup on the outer MPLS tree label and determines the MPLS forwarding table in which to lookup the inner MPLS label. This table is specific to the tree label space. The inner label is unique within the context of the root of the tree (as it is assigned by the root of the tree, without any coordination with any other nodes). Thus it is not unique across multiple roots. So, to unambiguously identify a particular VPLS one has to know the label, and the context within which that label is unique. The context is provided by the outer MPLS label [MPLS-UPSTREAM]. The outer MPLS label is stripped. The lookup of the resulting MPLS label determines the VSI in which the receiver PE needs to do the C- multicast data packet lookup. It then strips the inner MPLS label and sends the packet to the VSI for multicast data forwarding. Raggarwa, Kamite & Fang [Page 27] Internet Draft draft-ietf-l2vpn-vpls-mcast-02.txt September 2007 16. Security Considerations Security considerations discussed in [RFC4761] and [RFC4762] apply to this document. 17. IANA Considerations This document defines a new BGP optional transitive attribute, called P-Tunnel Attribute. 18. Acknowledgments Many thanks to Thomas Morin for his support of this work. We would also like to thank authors of [BGP-MVPN] as the details of the inter- AS segmented tree procedures in this document have benefited from those in [BGP-MVPN]. 19. Normative References [RFC2119] "Key words for use in RFCs to Indicate Requirement Levels.", Bradner, March 1997 [RFC3107] Y. Rekhter, E. Rosen, "Carrying Label Information in BGP-4", RFC3107. [RFC4761] K. Kompella, Y. Rekther, "Virtual Private LAN Service", draft-ietf-l2vpn-vpls-bgp-02.txt [RFC4762] M. Lasserre, V. Kompella, "Virtual Private LAN Services over MPLS", draft-ietf-l2vpn-vpls-ldp-03.txt [MPLS-UPSTREAM] R. Aggarwal, Y. Rekhter, E. Rosen, "MPLS Upstream Label Assignment and Context Specific Label Space", draft-ietf-mpls- upstream-label-00.txt [MPLS-MCAST] T. Eckert, E. Rosen, R. Aggarwal, Y. Rekhter, "MPLS Multicast Encapsulations", draft-ietf-mpls-multicast-encaps-00.txt Raggarwa, Kamite & Fang [Page 28] Internet Draft draft-ietf-l2vpn-vpls-mcast-02.txt September 2007 20. Informative References [VPLS-CTRL] R. Aggarwal, Y. Kamite, L. Fang, "Propagation of VPLS IP Multicast Group Membership Information", draft-raggarwa-l2vpn-vpls- mcast-ctrl-00.txt [L2VPN-SIG] E. Rosen et. al., "Provisioning, Autodiscovery, and Signaling in L2VPNs", draft-ietf-l2vpn-signaling-08.txt [MVPN] E. Rosen, R. Aggarwal, "Multicast in 2547 VPNs", draft-ietf- l3vpn-2547bis-mcast-02.txt" [MVPN-BGP] R. Aggarwal, E. Rosen, Y. Rekhter, T. Morin, C. Kodeboniya. "BGP Encodings for Multicast in 2547 VPNs", draft-ietf- l3vpn-2547bis-mcast-bgp-02.txt [RSVP-P2MP] R. Aggarwal et. al, "Extensions to RSVP-TE for Point to Multipoint TE LSPs", draft-ietf-mpls-rsvp-te-p2mp-07.txt [MLDP] I. Minei et. al, "Label Distribution Protocol Extensions for Point-to-Multipoint and Multipoint-to-Multipoint Label Switched Paths", draft-ietf-mpls-ldp-p2mp-02.txt [RFC4364] "BGP MPLS VPNs", E. Rosen, Y.Rekhter, February 2006 [MCAST-VPLS-REQ] Y. kamite, et. al., "Requirements for Multicast Support in Virtual Private LAN Services", draft-ietf-l2vpn-vpls- mcast-reqts-05.txt 21. Author Information Rahul Aggarwal Juniper Networks 1194 North Mathilda Ave. Sunnyvale, CA 94089 Email: rahul@juniper.net Yakov Rekhter Juniper Networks 1194 North Mathilda Ave. Sunnyvale, CA 94089 Email: yakov@juniper.net Yuji Kamite NTT Communications Corporation Tokyo Opera City Tower 3-20-2 Nishi Shinjuku, Shinjuku-ku, Tokyo 163-1421, Japan Email: y.kamite@ntt.com Luyuan Fang AT&T 200 Laurel Avenue, Room C2-3B35 Middletown, NJ 07748 Phone: 732-420-1921 Email: lufang@cisco.com Chaitanya Kodeboniya Raggarwa, Kamite & Fang [Page 29] Internet Draft draft-ietf-l2vpn-vpls-mcast-02.txt September 2007 22. 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