One document matched: draft-sajassi-mvpls-00.txt







            
            PPVPN Working Group                                          Ali Sajassi 
            Internet Draft                                            Hussein Salama 
            Expiration Date: May 2003                                  Cisco Systems 
                                                                       November 2002 
                                                                                 
             
           
                               VPLS based on IP Multicast 
                                             
                               draft-sajassi-mvpls-00.txt 
             
            Status of this Memo 
             
            This document is an Internet-Draft and is in full conformance with all 
            provisions of Section 10 of RFC2026.  
             
            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 obsolete 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 
             
            Virtual Private LAN Service (VPLS) is a type of Layer-2 Provider 
            Provisioned Virtual Private Network (L2 PPVPN) offered service, which 
            has been described in [PPVPN-FRWK]. If the Service Provider network 
            provides IP multicast functionality, then this network capability can 
            be leveraged in providing very efficient VPLS service and yet 
            simplifying the implementation of such service. This document describes 
            a solution for providing VPLS service based on IP multicast feature 
            referred to as Multicast Virtual Private LAN Service (MVPLS). 
             
             
             
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          1. Boilerplate for Sub-IP Area Drafts  
             
            RELATED DOCUMENTS 
            draft-ietf-ppvpn-l2-framework-00.txt 
            draft-lasserre-vkompella-ppvpn-vpls-02.txt 
             
            WHERE DOES IT FIT IN THE PICTURE OF THE SUB-IP WORK 
             
            Belongs in PPVPN 
             
            WHY IS IT TARGETED AT THIS WG 
             
            This document describes a mechanism for Virtual Private LAN Service 
            (VPLS), which is a type of Provider-Provisioned Layer 2 VPN offered 
            services. 
             
            JUSTIFICATION 
             
            This document describes a solution for providing VPLS, which is a type 
            of Layer-2 Provider Provision Virtual Private Network (L2 PPVPN) 
            offered service described in [PPVPN-FRWK] 
             
          2. Introduction 
             
            Virtual Private LAN Service (VPLS) is a type of Layer-2 Provider 
            Provisioned Virtual Private Network (L2 PPVPN) offered service, which 
            has been described in [PPVPN-FRWK]. VPLS emulates a LAN segment across 
            providerÆs MAN/WAN network such that to CE devices of a customer 
            (switches, routers, or hosts), it looks as if they are all on the same 
            LAN. A solution for providing such service is presented in [VPLS] that 
            describes how an architecture with a two-level hierarchy can be used to 
            provide this service in a scalable way. [VPLS] solution neither 
            discusses nor makes any assumptions regarding the auto-discovery 
            approach since the architecture is independent of it. However, it makes 
            an explicit assumption regarding the type of Pseudowire (PW) used in 
            the solution, which is Point-to-Point. 
             
            If the Service Provider network provides IP multicast functionality, 
            then this network capability can be leveraged in providing very 
            efficient VPLS service and yet simplifying the implementation of such 
            service. This document describes an alternative solution for providing 
            VPLS service based on IP multicast feature referred to as Multicast 
            Virtual Private LAN Service (MVPLS). 
             
            MPVLS utilizes both access and core network bandwidth very efficiently 
            by replicating broadcast/multicast and unknown unicast frames as close 
           
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            to the egress PE as possible. It also simplifies the service 
            implementation since it has an inherent auto-discovery mechanism and 
            thus there is no need for explicit mechanisms such as [BGP-AUTODISC] or 
            [DNS-AUTODISC]. Also for the default case of IP network, the operation 
            gets further simplified since there is no need for signaling of PWs 
            (e.g., L2TPv3 encapsulation can be used without the corresponding 
            signaling protocol). 
             
            MVPLS relies on two key components: 
             
               MultiPoint-to-Point Pseudowire (MPtP PW): This PW is intended for 
               known unicast Ethernet frames and it is associated with a single 
               Attachment Circuit (AC) of a VPLS. Using this PW, the ingress PE can 
               forward a packet to a specific AC on the egress PE.  
                
               MultiPoint-to-MultiPoint Pseudowire (MPtMP PW): This PW is intended 
               for unknown unicast frames or broadcast/multicast frames and it is 
               associated with a VPLS instance. Using this PW, the ingress PE can 
               forward a packet to all the ACs on the egress PEs associated with 
               this VPLS instance.  
             
            Each MPtP PW is represented by a unique unicast IP address and each 
            MPtMP PW is also represented by a unique IP multicast group address. A 
            MPtP PW usually represents a single AC (although there are some 
            exceptions as will be seen later) and a MPtMP PW represents a single 
            VPLS instance. Since the IP address for MPtP PW corresponds to a 
            specific AC on the egress PE (e.g., to a sub-interface on the egress 
            PE), there is no need to do MAC address lookup for packet forwarding at 
            the egress PE, which makes the operation more efficient for the egress 
            PE. However, at the ingress PE, the MAC address lookup is needed in 
            order to select the proper MPtP PW associated with a given destination 
            MAC address (MAC DA). Therefore, in contrast to [VPLS], the forwarding 
            operation of MVPLS is asymmetric and MAC address lookup for packet 
            forwarding is only used at the ingress PE. 
             
             
          3. Overview 
             
            The following figure shows the MVPLS topology. The service provider 
            backbone network can be either IP-based or MPLS-based. In the following 
            sections, we discuss the operation of MVPLS over an IP backbone. 
            Special considerations for the case of an MPLS backbone are discussed 
            in Section 10.1. 
           
            As shown in the figure, the CEs can either be directly connected to a 
            PE or they can be connected via an aggregator device referred to as U-
           
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            PE (User facing PE) in which case the PE itself is referred to N-PE 
            (Network facing PE) with respect to those CEs. For example, CE1, CE1Æ, 
            CE2, CE2Æ, and CE3 are directly connected to their corresponding PEs. 
            For this case, a customer AC can be identified by the physical port 
            identifier or, in the case of customers using VLANs, by the combination 
            of the physical port plus the customerÆs VLAN identifier. This draft 
            uses this case as a basis for discussion. Also in the figure below, the 
            U-PE aggregates the ACs from CE4 and CE4Æ and tunnels them to the N-PE 
            using QinQ. Special considerations for this case are discussed in 
            Section 10.2. 
             
            +----+                                                     +----+    
            +CE1 +--+                                  +---------------|CE2 |  
            +----+  |    ........................      |               +----+  
            MVPLS A |  +------+               +------+ |               MVPLS A  
                    +--| PE   |-- Service ----| PE   |-+------+       +----+  
                       +------+   Provider    | N-PE |        +-------|CE2Æ|  
                       / .        Backbone    +------+                +----+  
                      /  .          |           .  \                  MVPLS B        
            +----+   /   .          |           .   \     
            +CE1Æ+--+    .          |           .    \  
            +----+       .        +----+        .     \ QinQ 
            MVPLS B      .........| PE |.........      \ 
                                  +----+                \     
                                    |                    \  
                                    |                     \                          
                                  +----+               +------+   +----+  
                                  |CE3 |               | U-PE |---|CE4 |  
                                  +----+               +------+   +----+  
                                  MVPLS A                 |       MVPLS A  
                                                          |  
                                                          |      +----+  
                                                          +------|CE4Æ|   
                                                                 +----+  
                                                                  MVPLS B 
             
           
            A customer CE is attached to a PE via the corresponding AC. Each AC is 
            associated with one VPLS instance and furthermore a unique IP address 
            is assigned to each AC. This IP address is used for pseudo-wire 
            identification and is used by the ingress PE to forward a unicast 
            packet directly to a specific AC on the egress PE without the need for 
            MAC address lookup on the egress PE. This will be discussed in detail 
            in Section 4. 
           
           
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            Some devices do not have the ability to have a unique IP address 
            assigned to each AC (e.g., interface/sub-interface). Such a device 
            should be configured with one IP address for each VPLS instance that is 
            active on that device. The Forwarding operation at the egress PE is 
            different in that case and will be discussed in Section 9. 
             
            MVPLS associates one IP multicast group with each VPLS instance. Each 
            PE that participates in a given VPLS must join the corresponding IP 
            multicast group. The resulting multicast tree(s) is a MPtMP PW. All 
            multicast frames, broadcast frames, and frames to an unknown 
            destination for a given VPLS instance are forwarded to the multicast 
            group address corresponding to that VPLS.  
           
            MVPLS has several advantages when compared to the unicast-based VPLS 
            schemes. The use of multicast results in efficient packet replication. 
            Packets are replicated as close as possible to the egress PE(s), which 
            results in efficient use of the network bandwidth and relieves the 
            ingress PE from having to replicate the packets to all destinations. 
             
            The use of IP multicast also eliminates the need for a dedicated auto-
            discovery mechanism. In MVPLS, a PE does not need to discover the IDs 
            and/or addresses of the other PEs participating in the same VPLS 
            instance. When a PE joins the multicast group corresponding to a given 
            VPLS instance, it can reach all other PEs participating in the same 
            VPLS instance without needing to have explicit knowledge of their 
            identities. 
             
            Another reason why a PE does not need to explicitly know the 
            identities/IP addresses of the other PEs is that there is no PE-
            specific pseudo-wire signaling in MVPLS. 
             
            Finally, MVPLS does not use VPN-ids. In MVPLS, pseudo-wires are 
            uniquely identified using IP addresses only. Therefore, there is no 
            need to carry VPN-id or session-id inside the PW PDU. 
           
            The multicast group address associated with a given VPLS must be 
            provisioned on each PE which participates in that VPLS. Therefore, a 
            multicast group address in a PE identifies a VPLS instance and its 
            associated forwarding table on that PE. When an AC is configured in a 
            PE, it is associated with a VPN-id, which in turn corresponds to a 
            unique multicast group address. The VPN-id can be the same as multicast 
            group address or it can be a standard ID that corresponds to a 
            multicast group address. 
             
           
           
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          4. Pseudo-Wires 
             
          4.1. Multipoint-to-Point Pseudo-Wire 
           
            One MPtP PW is created for every AC. No explicit signaling is required 
            for creating this MPtP PW. The pseudo-wire is identified using the IP 
            address assigned to that AC (i.e., the IP address assigned to the 
            interface/sub-interface corresponding to that AC). 
             
            An ingress PE encapsulates a unicast frame to a known destination 
            (i.e., a MAC DA for which an entry exists in the forwarding table at 
            the ingress PE) with an IP header. The ingress PE sets the destination 
            IP address in the IP header to the IP address associated with the 
            destination AC (-i.e., the AC over which the MAC DA has been learned).  
           
          4.2. Multipoint-to-Multipoint Pseudo-Wire 
             
            A single MPtMP PW is created for each VPLS instance. This PW is 
            identified by a unique IP multicast group address. A PE connects to the 
            MPtMP PW for a given VPLS instance by joining the corresponding 
            multicast group using standard multicast tree construction mechanisms 
            (e.g., by initiating a PIM Join). When the first AC is configured for a 
            VPLS instance in a PE, that PE joins the multicast group. All 
            subsequent ACs that get configured for that VPLS instance donÆt trigger 
            any additional join messages to be sent from that PE. However, the ACs 
            do join the multicast group on that PE but this is an internal process 
            for that PE. When ACs for a VPLS instance get decommissioned, no 
            withdrawal messages get sent out from that PE unless the last AC for 
            that VPLS instance get decommissioned. In this case, the PE withdraws 
            from the multicast group (e.g., the PE sends out a PIM Prune message). 
            Multiple multicast tree protocols exist. The choice of a specific 
            multicast protocol will be discussed in Section 12. 
           
            All broadcast frames, multicast frames, and unicast frames to unknown 
            destinations (i.e., MAC addresses for which no entry exists in the 
            forwarding table at the ingress PE) are forwarded over the MPtMP PW to 
            all destination PEs associated with that VPLS. These frames are 
            encapsulated with an IP header. The ingress PE sets the destination IP 
            address in the IP header to the IP multicast group address associated 
            with that VPLS instance.  
             
             
          5. Encapsulation 
           
            Both MPtP and MPtMP PWs have the same encapsulation format. An Ethernet 
            frame is encapsulated with an L2TPV3 header (or modified version of it) 
           
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            and an IP header. The source IP address is set to the address 
            associated with the AC from which the ingress PE received the frame. 
            The destination IP address is set to the IP address identifying the 
            associated PW. In case of a MPtP PW, this is a unicast IP address and 
            in case of a MPtMP PW, this is an IP multicast group address. 
           
           
          6. The Forwarding Table 
             
            Although the MAC address lookup is performed only on the ingress PE as 
            mentioned previously, the MAC address learning is done at both ingress 
            and egress PEs. In the ingress PE, source MAC addresses (MAC SAs) are 
            learned in relationship to the ACs over which they are received; 
            whereas, in the egress PE, MAC SAs are learned in relationship to the 
            PWs over which they are received. Therefore, the forwarding table for a 
            given VPLS instance contains MAC addresses and their corresponding 
            adjacencies information. An adjacency information entry can represent 
            either an AC or a PW. In case of an AC, it represents port-id or port-
            id + VLAN-id and in case of a PW, it represents PW IP-address.  
             
           
          7. Auto-Discovery and Pseudo-Wire Signaling 
             
            In [VPLS], auto-discovery is used to discover member PEs belonging to 
            the same VPLS instance and then a PtP signaling channel is established 
            for PW signaling between a given PE and all other discovered PEs. 
            However, as previously noted, MVPLS does not use any explicit auto-
            discovery mechanisms since PEs participating in the same VPLS instance 
            do not need to setup any point-to-point signaling channel and thus they 
            do not need to gain explicit knowledge of one another.  
             
            Auto-discovery for MVPLS is done implicitly through the IP multicast 
            mechanism and a PE becomes a member of the VPLS by joining the 
            corresponding multicast tree. When a PE is configured with a new AC, it 
            is also configured with the VPN-id that corresponds to the multicast 
            group address of the MPtMP PW for that VPLS instance. Assuming no other 
            ACs associated with the same VPLS instance are already configured on 
            that PE, the PE immediately joins that multicast group, and starts 
            receiving IP multicast packets whose MPtMP PW payload contains Ethernet 
            broadcast/multicast frames and unknown unicast frames.  The PE uses a 
            MPtMP PW associated with a VPLS instance to discover the MPtP PWs 
            associated with the same VPLS instance and also to announce to other 
            PEs the MPtP PW associated with the newly configured AC. 
             
             
           
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          8. Forwarding and Learning Operations 
             
          8.1. MAC Address Learning at Ingress PE 
           
            When an ingress PE receives an Ethernet frame from a specific AC, it 
            looks up the MAC SA of the frame in the corresponding forwarding table. 
            If the MAC SA is not found, the PE learns the new source address and 
            adds an entry to the forwarding table for that new address. The 
            forwarding information for that new entry is set to AC-id over which 
            the MAC SA is learned. The AC-id can be either a port-id or port-id + 
            vlan-id. In cases where, the AC is a non-Ethernet type (e.g., ATM or FR 
            VC), then the AC-id is the id of the corresponding VC. 
             
            The ingress PE then continues processing the frame as will be discussed 
            in Sections 8.3 and 8.4. 
             
           
          8.2. MAC Address Learning at Egress PE 
             
            When an egress PE receives an MVPLS packet from the core, it determines 
            which VPLS this packet is associated with based on the destination IP 
            address of the packet. The egress PE then looks up the MAC SA of the 
            frame in the forwarding table. If the source address is not found, the 
            PE learns the new source address and adds an entry for that new address 
            to the table. The forwarding information for that new entry is set to 
            MPtP PW-id which is the unicast IP address associated with the MPtP PW.  
             
            The egress PE then continues processing the frame as will be discussed 
            in Sections 8.3 and 8.4. 
             
             
          8.3. Forwarding of Known-MAC-DA Unicast Frames 
             
            After the ingress PE performs the MAC SA lookup, and learning (if 
            needed), as has been described in Section 8.1, the ingress PE checks 
            the MAC DA. If the destination address is a unicast address, the 
            ingress PE looks up this address in the forwarding table for that VPLS 
            instance. If an entry is found, one of the following two actions is 
            taken: 
                  . If the entry is an AC-id, then encapsulating the Ethernet 
                    frame with L2TPv3 header and IP header may or may not be 
                    needed depending on the internal architecture of the PE. If 
                    needed, then it gets handled the same way as PW VC type. 
                    Otherwise, the frame is directly forwarded to the destination 
                    AC.  
           
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                  . If the entry is a PW-id, then the ingress PE encapsulates the 
                    frame with an L2TPv3 header and an IP header. The source IP 
                    address is set to the address of the AC over which the frame 
                    arrived and the destination IP address is set to the PW IP 
                    address looked up in the VPLS forwarding table. The ingress 
                    PE then forwards the IP packet into the core. 
             
            When an egress PE receives a unicast MVPLS packet from the core, it 
            performs the MAC SA lookup, and possibly learning, as has been 
            described in Section 8.2. The egress PE does not lookup the MAC DA of 
            the received frame since the destination IP address of the received 
            packet readily identifies the interface associated with the AC. The 
            packet is immediately delivered to that interface. The IP header and 
            the L2TPv3 header are removed before the Ethernet frame gets forwarded 
            over the AC towards its destination. 
             
             
          8.4. Forwarding of Unknown-MAC-DA Unicast or Multicast/Broadcast Frames 
             
            After the ingress PE performs the MAC SA lookup, and learning (if 
            needed), as has been described in Section 8.1, the ingress PE checks 
            the MAC DA. If the destination address is a unicast address, the 
            ingress PE looks up this address in the forwarding table for that VPLS 
            instance. If no entry exists for this destination address, the frame 
            must be broadcast to all sites participating in that VPLS. The 
            following actions must be taken: 
                  . The ingress PE replicates the frame to all local ACs 
                    participating in the same MVPLS, except the AC over which the 
                    frame has arrived. 
                  . The ingress PE encapsulates the frame with an L2TPv3 header 
                    and an IP header. The source IP address is set to the address 
                    of the Attachment VC over which the frame arrived and the 
                    destination IP address is set to the IP multicast group 
                    address associated with the VPLS instance. The ingress PE 
                    then forwards the packet into the core. Replication of this 
                    multicast packet is done efficiently by the multicast enabled 
                    PE routers and the core routers. 
             
            All PEs participating in a given VPLS, except the ingress PE, receive 
            the multicast packet. When an egress PE receives an MVPLS packet from 
            the core, it identifies the corresponding VPLS instance based on the 
            destination multicast group address and it replicates and forwards the 
            packet to all the destination ACs associated with that multicast group 
            address (with that VPLS instance). It also performs the MAC SA lookup, 
            and learning if needed, as has been described in Section 8.2.  
           
           
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          9. MAC Address Lookup on Egress PEs 
           
            So far, we assumed that each AC is assigned to a unique IP address and 
            thus can be associated with a unique MPtP PW. This implies that the 
            packet encapsulation/ decapsulation is done at the ACs (customer-facing 
            interfaces). However, some PEs are not capable of performing PW 
            processing at their ACs and thus a MPtP PW can not be extended all the 
            way to an AC. In this case, the PE assigns a unique IP address to each 
            VPLS instance instantiated on it. Therefore, the MPtP PW is associated 
            with a VPLS instance for that PE instead of an AC. In such scenarios, 
            the packet forwarding on the egress PE for a MPtP PW requires MAC 
            address lookup on the egress PE in order to select the appropriate AC. 
            Besides this difference, the rest of the operation for MPtP and MPtMP 
            remains same as before. 
             
             
          10. Other Network Types  
           
          10.1. MPLS Network 
             
            So far, our discussion only considered implementing MVPLS over an IP 
            core. However, MVPLS is independent of the core transport. It can also 
            be implemented over an MPLS core. In that case each MPtP PW will 
            correspond to one MPLS LSP (one-to-one mapping). To make this possible, 
            the IGP running in the core must not aggregate the IP addresses used to 
            identify the MPtP PWs. Since thereÆs a one-to-one mapping between MPtP 
            PWs and MPLS LSPs, an egress PE can forward an MPLS packet arriving 
            from the core to the appropriate AC based on the MPLS label without 
            having to look it up in the forwarding table. This forwarding behavior 
            for MPtP PW is the same as the one in IP networks.  
             
            The situation is more complicated for transporting IP multicast over an 
            MPLS core. A framework for transporting IP multicast over MPLS is 
            presented in [MC-MPLS]. However, no standard solutions for that problem 
            exist yet. Therefore, we propose transporting the MPtMP PWÆs traffic 
            using IP multicast packets across the core as before, i.e., without 
            MPLS encapsulation. 
             
             
          10.2. QinQ Access Network 
           
            MVPLS supports QinQ access network very easily and the operation is 
            basically the same as before with just one small change to AC 
            identification. Since the packets that come to the N-PE, carry double 
            VLAN tags and the outer tag (ProviderÆs VLAN û P-VLAN) represents the 
            VPLS instance, then the P-VLAN needs to be used in the AC 
           
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            identification of the N-PE. If the offered service is TLS and thus 
            transparent to the customerÆs VLANs, then the AC on the N-PE is 
            identified by Port + P-VLAN. However, if the offered service is per 
            customer VLAN (C-VLAN), then the AC needs to be identified by port + P-
            VLAN + C-VLAN. 
             
            Once an AC is identified, then the association of that AC to MPtP PW or 
            MPtMP PW is done exactly as described before. Also forwarding of 
            unicast and broadcast/multicast packets from/to the AC to/from the MPtP 
            PW or the MPtMP PW is performed same as before. MAC address learning 
            associated with the ACs also works the same way except the AC is now 
            represented by this new id.   
             
           
             
          11. Packet Ordering 
             
            Since MVPLS uses a MPtMP PW (for unknown unicast frames) which is 
            different from MPtP PW, there can be situations where the unicast 
            frames arrive at the destination out of sequence. For example, a 
            unicast frames with unknown MAC DA gets sent over MPtMP PW; whereas, as 
            soon as that MAC DA is learned it gets sent over the MPtP PW. If the 
            MPtMP path has longer delay than MPtP path, then there can be 
            situations where two consecutive frames can arrive at the destination 
            out of sequence. To alleviate this situation, the delay through MPtMP 
            path should be minimized and be close to the one for MPtP path. The 
            closer the delay of MPtMP path to MPtP path, the less chances of out-
            of-sequence delivery such that if the delay between the two paths is 
            the same, then there is no possibility for out-of-sequence delivery in 
            steady state. 
             
             
          12. Multicast choice 
              
            Multiple IP multicast mechanisms exist. One main differentiation of IP 
            multicast today is the service available to a host. [IP-MC] describes 
            the traditional IP multicast service model, which today is being called 
            ASM (Any Source Multicast). In ASM, a receiver host simply joins an IP 
            multicast group and receives the traffic from all source sending to 
            that group. [SSM] describes a different service model, SSM (Source 
            Specific Multicast), which differs from ASM in that it requires a 
            receiver to explicitly specify from which source it wants to receive IP 
            multicast traffic sent to a particular IP multicast group. In MPVLS, 
            the PE function requires ASM because it relies on the automatic 
            discovery of sources (i.e., other MVPLS PE devices) sending to an IP 
            multicast group. 
           
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            For ASM, various IP multicast routing protocols exist. Choosing the 
            right one has effects on the performance of the MVPLS service. 
             
             
             
            Two ASM-based IP multicast routing protocols that have existing 
            implementations and exhibit scaling and performance characteristics 
            that make them suitable for deployment in a service providerÆs backbone 
            network are PIM SM and PIM Bidir. Both protocols can be used with 
            MVPLS. PIM SM constructs one shortest path tree for each (S,G) pair, 
            where S is a source address and G is a multicast group address. PIM 
            Bidir, on the other hand, constructs a single tree to be shared by all 
            sources transmitting to the same multicast group G. The shared tree is 
            denoted a (*,G) tree. The use of multiple trees in the case of PIM SM 
            requires the network to maintain more state than the use of a single 
            tree in the case of PIM Bidir. However, PIM SMÆs shortest path trees 
            result in more optimal forwarding paths. In PIM SM, a destination 
            initially joins a shared (*,G) tree for a given multicast group. The 
            destination then discovers the active sources for that multicast group 
            via the shared (*,G) tree and joins the shortest path (S,G) tree of 
            each of these active sources. 
             
            Note that even though PIM Bidir constructs a sub-optimal shared 
            forwarding tree, MVPLS using PIM Bidir still results in more efficient 
            utilization of the network bandwidth than the unicast-based VPLS 
            solutions, which require the ingress PE to replicate all broadcast 
            frames, multicast frames, and frames to unknown destinations to all 
            egress PEs associated with the same VPLS. 
             
            MVPLS implementations should use multicast group addresses from the 
            administratively scoped address range, 239.0.0.0 to 239.255.255.255 
            [SCPD-MC]. The MVPLS multicast trees should be bounded by the service 
            providers PE routers. Hosts or routers outside the service providerÆs 
            backbone should not be permitted to join the MVPLS multicast trees. 
            Mechanisms for bounding the scope of a multicast tree exist but are 
            outside the scope of this draft. 
           
             
          13. Security Considerations 
              
            The security aspects of this solution will be discussed at a later 
            time. 
             
          14. Acknowledgements 
             
           
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            The authors would like to thank Toerless Eckert for his helpful 
            discussions and feedbacks. 
             
             
          15. References 
             
            [VPLS] ôVirtual Private LN Service over MPLSö, Lasserre et al, draft-
            lasserre-vkompella-ppvpn-vpls-02.txt, June 2002 (work in progress) 
             
            [PPVPN-FRWK] ôPPVPN L2 Frameworkö,  Loa Anderson,  draft-ietf-ppvpn-l2-
            framework-01.txt 
             
            [BGP-AUTODISC] ôUsing BGP as an Auto-Discovery Mechanism for Network 
            Based VPNsö, Ould-Brahim et al., draft-ietf-ppvpn-bgpvpn-auto-02.txt, 
            February 2002, (work in progress) 
             
            [DNS-AUTODISC] ôDNS/LDP Based VPLSö, Juha Heinanen, draft-heinanen-dns-
            ldp-vpls-00.txt, January 2002 (work in progress) 
             
            [MC-MPLS] "Overview of IP Multicast in a Multi-Protocol Label Switching 
            (MPLS) Environment", D. Ooms, RFC 3353 
             
            [IP-MC] "Host Extensions for IP Multicasting", S. Deering et. al., RFC 
            1112 
             
            [PIM-SM] "Protocol Independent Multicast-Sparse Mode (PIM-SM): Protocol 
            Specification", D. Estrin et. al., RFC 2362 
             
            [PIM-BIDIR] "Bi-directional Protocol Independent Multicast (BIDIR-
            PIM)", M. Handley et. al., draft-ietf-pim-bidir-04.txt 
             
            [SSM] "An Overview of Source-Specific Multicast (SSM)", S. 
            Bhattacharyya et. al., draft-ietf-ssm-overview-04.txt 
             
            [SCPD-MC] "Administratively Scoped IP Multicast", D. Meyer, RFC 2365 
             
             
          16. Authors' Addresses 
             
            Ali Sajassi 
            Cisco Systems, Inc. 
            170 West Tasman Drive 
            San Jose, CA  95134 
            Email: sajassi@cisco.com 
             
            Hussein Salama 
           
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            Cisco Systems, Inc. 
            170 West Tasman Drive 
            San Jose, CA  95134 
            Email: hsalama@cisco.com 
           
             
             
           
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