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Versions: (draft-serbest-l2vpn-vpls-mcast) 00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 RFC 7117

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
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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



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   only to a specified set of one or more IP multicast streams from one
   or more VPLSs are also described.

















































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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



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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].









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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.






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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.



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   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



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   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 <C-Source, C-Group>
   entries bound to this tree along with the Selective Tree Identifier.
   The inner label assigned for each <C-Source, C-Group> MUST be
   included if <C-Source, C-Group>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



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   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



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   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 <Route-
   Distinguisher (RD), VPLS Edge Device Identifier (VE-ID)> tuple. The
   NLRI defined in [RFC4761] comprises the <RD, VE-ID> 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 <RD,
   VE-ID> 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 <RD, VE-ID>. 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



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   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



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   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.








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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.






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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



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   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



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   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



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   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 <RD, VE ID> 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.





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   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.




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   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.






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     + 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



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       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 <RD, VE ID> 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



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   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
   <RD, VE-ID> 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



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   tree, as identified by the P-Tunnel Attribute, is an intra-AS LSP
   segment that is part of the inter-AS Tunnel for the <VPLS, VE ID>
   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 <C-Source,
   C-Group> 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 <C-
   Source, C-Group> 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 <C-Source, C-Group> as the addresses could
   overlap between different VPLS instances.
      2. The inner label allocated by the Selective Tree root for the
   <C-Source, C-Group>. 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



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   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 <C-S, C-G> entires. The source PE, that
   originates the Selective Tree, and the egress PEs, MUST to switch to
   the Selective Tree for the <C-S, C-G> entries that are mapped to it.

   Once a source PE decides to setup an Selective Tree, it announces the
   mapping of the <C-S, C-G> 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 <C-S, C-G>
   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 <C-S, C-G> 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 <C-S, C-G> 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.








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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.




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       When the type is set to LDP P2MP LSP, the Tunnel Identifier is
       <P-Root Node Address, Variable length opaque identifier>.

       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 <C-S,
   C-G> 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.








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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.








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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











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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





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22. Intellectual Property Statement

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   pertain to the implementation or use of the technology described in
   this document or the extent to which any license under such rights
   might or might not be available; nor does it represent that it has
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   on the procedures with respect to rights in RFC documents can be
   found in BCP 78 and BCP 79.

   Copies of IPR disclosures made to the IETF Secretariat and any
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   http://www.ietf.org/ipr.

   The IETF invites any interested party to bring to its attention any
   copyrights, patents or patent applications, or other proprietary
   rights that may cover technology that may be required to implement
   this standard.  Please address the information to the IETF at ietf-
   ipr@ietf.org.



23. Full Copyright Statement

   Copyright (C) The IETF Trust (2007).  This document is subject to the
   rights, licenses and restrictions contained in BCP 78, and except as
   set forth therein, the authors retain all their rights.

   This document and the information contained herein are provided on an
   "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
   OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND
   THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS
   OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF
   THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
   WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.












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