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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 (Editor)
Internet Draft                                          Juniper Networks
Category: Standards Track
Expiration Date: August 2012                                   Y. Kamite
                                                      NTT Communications

                                                                 L. Fang
                                                      Cisco Systems, Inc

                                                       February 02, 2012


                           Multicast in VPLS


                   draft-ietf-l2vpn-vpls-mcast-10.txt

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   include Simplified BSD License text as described in Section 4.e of
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   This document may contain material from IETF Documents or IETF
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   than English.


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 SP network can be used to carry traffic
   belonging only to a specified set of one or more IP multicast streams
   from one or more VPLSes are also described.
























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Table of Contents

 1          Specification of requirements  .........................   4
 2          Contributors  ..........................................   4
 3          Terminology  ...........................................   5
 4          Introduction  ..........................................   5
 5          Existing Limitations of VPLS Multicast  ................   6
 6          Overview  ..............................................   6
 6.1        Inclusive and Selective Multicast Trees  ...............   6
 6.2        BGP-Based VPLS Membership Auto-Discovery  ..............   8
 6.3        IP Multicast Group Membership Discovery  ...............   8
 6.4        Advertising P-Multicast Tree to VPLS/C-Multicast Binding  ..9
 6.5        Aggregation  ...........................................   9
 6.6        Inter-AS VPLS Multicast  ...............................  10
 7          Intra-AS Inclusive P-Multicast Tree A-D/Binding  .......  11
 7.1        Originating intra-AS VPLS auto-discovery routes  .......  12
 7.2        Receiving intra-AS VPLS auto-discovery routes  .........  13
 8          Demultiplexing P-Multicast Tree Traffic  ...............  14
 8.1        One P-Multicast Tree - One VPLS Mapping  ...............  14
 8.2        One P-Multicast Tree - Many VPLS Mapping  ..............  14
 9          Establishing P-Multicast Trees  ........................  15
 9.1        Common Procedures  .....................................  15
 9.2        RSVP-TE P2MP LSPs  .....................................  16
 9.2.1      P2MP TE LSP - VPLS Mapping  ............................  16
 9.3        Receiver Initiated MPLS Trees  .........................  17
 9.3.1      P2MP LSP - VPLS Mapping  ...............................  17
 9.4        Encapsulation of Aggregate P-Multicast Trees  ..........  17
10          Inter-AS Inclusive P-Multicast Tree A-D/Binding  .......  17
10.1        VSIs on the ASBRs  .....................................  18
10.1.1      Option (a): VSIs on the ASBRs  .........................  18
10.1.2      Option (e): VSIs on the ASBRs  .........................  18
10.2        Option (b) - Segmented Inter-AS Trees  .................  19
10.2.1      Segmented Inter-AS Trees VPLS Inter-AS A-D/Binding  ....  19
10.2.2      Propagating BGP VPLS A-D routes to other ASes: Overview  ...20
10.2.2.1    Propagating Intra-AS VPLS A-D routes in E-BGP  .........  21
10.2.2.2    Inter-AS A-D route received via E-BGP  .................  22
10.2.2.3    Leaf A-D Route received via E-BGP  .....................  24
10.2.2.4    Inter-AS A-D Route received via I-BGP  .................  24
10.3        Option (c): Non-Segmented Tunnels  .....................  25
11          Optimizing Multicast Distribution via Selective Trees  .  26
11.1        Protocol for Switching to Selective Trees  .............  28
11.2        Advertising C-(S, G) Binding to a Selective Tree  ......  28
11.3        Receiving S-PMSI A-D routes by PEs  ....................  31



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11.4        Inter-AS Selective Tree  ...............................  32
11.4.1      VSIs on the ASBRs  .....................................  33
11.4.1.1    VPLS Inter-AS Selective Tree A-D Binding  ..............  33
11.4.2      Inter-AS Segmented Selective Trees  ....................  33
11.4.2.1    Handling S-PMSI A-D routes by ASBRs  ...................  34
11.4.2.1.1  Merging Selective Tree into an Inclusive Tree  .........  35
11.4.3      Inter-AS Non-Segmented Selective trees  ................  36
12          BGP Extensions  ........................................  36
12.1        Inclusive Tree/Selective Tree Identifier  ..............  36
12.2        MCAST-VPLS NLRI  .......................................  37
12.2.1      S-PMSI auto-discovery route  ...........................  37
12.2.2      Leaf auto-discovery route  .............................  39
13          Aggregation Considerations  ............................  39
14          Data Forwarding  .......................................  40
14.1        MPLS Tree Encapsulation  ...............................  40
14.1.1      Mapping multiple VPLS instances to a P2MP LSP  .........  40
14.1.2      Mapping one VPLS instance to a P2MP LSP  ...............  41
15          VPLS Data Packet Treatment  ............................  42
16          Security Considerations  ...............................  43
17          IANA Considerations  ...................................  43
18          Acknowledgments  .......................................  44
19          Normative References  ..................................  44
20          Informative References  ................................  44
21          Author's Address  ......................................  46






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




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3. Terminology

   This document uses terminology described in [RFC4761] and [RFC4762].


4. Introduction

   [RFC4761] and [RFC4762] describe a solution for VPLS multicast that
   relies on the use of P2P RSVP-TE or MP2P LDP LSPs, referred to as
   Ingress Replication in this document. This solution has certain
   limitations for certain VPLS multicast traffic profiles. For example
   it may result in highly non-optimal bandwidth utilization in the MPLS
   network when large amount of multicast traffic is to be transported

   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 Service Provider (SP) network to carry all the multicast
   traffic from one or more VPLS sites connected to a given PE,
   irrespective of whether these sites belong to the same or different
   VPLSes. 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 one VPLS.

   This document also provides procedures by which a single multicast
   distribution tree in the SP network can be used to carry traffic
   belonging only to a specified set of IP multicast streams, originated
   in one or more VPLS sites connected to a given PE, irrespective of
   whether these sites belong to the same or different VPLSes.  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 VPLSes. This allows multicast traffic, by default, to be
   carried on an Inclusive tree, while traffic from some specific
   multicast streams, e.g., high bandwidth streams, could be carried on
   one of the "Selective trees".












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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.

   Ingress Replication may be an acceptable 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
   learns the destination MAC address of those unicast packets, MAY
   still use ingress replication.


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 [RFC4875] 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 on a given link. 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 tunnels are P2MP LSPs signaled by either
   P2MP RSVP-PE or mLDP [MLDP].

   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, multicast 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. This option supports the use of a single
   multicast distribution tree, referred to as an Inclusive P-Multicast
   tree, in the SP network to carry all the multicast traffic from a
   specified set of VPLS sites connected to a given PE. There is no
   assumption made with respect to whether this traffic is IP
   encapsulated or not. A particular P-Multicast tree can be set up to



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   carry the traffic originated by sites belonging to a single VPLS, or
   to carry the traffic originated by sites belonging to different
   VPLSes. The ability to carry the traffic of more than one VPLS on the
   same tree is termed Aggregation. The tree needs to include every PE
   that is a member of any of the VPLSes 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 that are interested in
   receiving traffic for that stream.

   An Inclusive P-Multicast tree as defined in this document is a P2MP
   tree.  A P2MP tree is used to carry traffic only from VPLS sites that
   are connected to the PE that is the root of the tree.

       2. Selective trees. A Selective P-Multicast tree is used by a PE
   to send IP multicast traffic for one or IP more specific multicast
   streams, received by a PE over PE-CE interfaces that belong to the
   same or different VPLSes, to a subset of the PEs that belong to those
   VPLSes. 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 VPLSes is termed Aggregation. The reason for
   having Selective P-Multicast trees is to provide a PE the ability to
   create separate SP multicast trees for specific multicast streams,
   e.g. high bandwidth multicast streams. This allows traffic for these
   multicast streams to reach only those PE routers that have receivers
   in these streams. This avoids flooding other PE routers in the VPLS.

   A SP can use both Inclusive P-Multicast trees and Selective P-
   Multicast trees or either of them for a given VPLS on a PE, based on
   local configuration.  Inclusive P-Multicast trees can be used for
   both IP and non-IP data multicast traffic, while Selective P-
   Multicast trees must be used only for IP multicast data traffic. The
   use of Selective P-Multicast trees for non-IP multicast traffic is
   outside the scope of this document.

   A variety of transport technologies may be used in the SP network.
   For inclusive P-Multicast trees, these transport technologies include
   point-to-multipoint LSPs created by RSVP-TE or mLDP. For selective P-
   Multicast trees, only unicast PE-PE tunnels (using MPLS or IP/GRE
   encapsulation) and P2MP LSPs are supported, and the supported P2MP
   LSP signaling protocols are RSVP-TE, and mLDP. Other transport
   technologies are outside the scope of this document.

   This document also describes the data plane encapsulations for
   supporting the various SP multicast transport options.






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6.2. BGP-Based VPLS Membership Auto-Discovery

   In order to establish Inclusive P-Multicast trees for one or more
   VPLSes, when Aggregation is performed or when the tunneling
   technology is P2MP RSVP-TE, the root of the tree must be able to
   discover the other PEs that have membership in one or more of these
   VPLSes. This document uses the BGP-based procedures described in
   [RFC4761] and [L2VPN-SIG] for discovering the VPLS membership of all
   PEs.

   The leaves of the Inclusive P-Multicast trees must also be able to
   auto-discover the identifier of the tree. This is described in
   section 6.4.


6.3. IP Multicast Group Membership Discovery

   The setup of a Selective P-Multicast 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 (C-S, C-G)s, in the following
   cases:

     + When aggregation is used OR

     + When the tunneling technology is P2MP RSVP-TE

     +  If ingress replication is used and the ingress PE wants to send
       traffic for (C-S, C-G)s to only those PEs that are on the path to
       receivers to the (C-S,C-G)s.


   For discovering the IP multicast group membership, this document
   describes procedures that allow an ingress PE to enable explicit
   tracking. Thus an ingress PE can request the IP multicast membership
   from egress PEs for one or more C-multicast streams. These procedures
   are described in section "Optimizing Multicast Distribution via
   Selective Trees".

   These procedures are applicable when IGMP is used as the multicast
   signaling protocol between the VPLS CEs. They are also applicable
   when PIM as specified in [RFC4601] is used as the multicast routing
   protocol between the VPLS CEs and PIM join suppression is disabled on
   all the CEs. However these procedures do not apply when PIM is used
   as the multicast routing protocol between the VPLS CEs and PIM join
   suppression is not disabled on all the CEs. Procedures for this case
   are for further study.

   The leaves of the Selective P-Multicast trees must also be able to



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   discover the identifier of the tree. This is described in section
   6.4.


6.4. Advertising P-Multicast Tree to VPLS/C-Multicast Binding

   This document describes procedures based on BGP VPLS Auto-Discovery
   (A-D) that are used by the root of an Aggregate P-Multicast tree to
   advertise the Inclusive or Selective P-Multicast tree binding and the
   de-multiplexing information to the leaves of the tree. This document
   uses the PMSI Tunnel attribute [BGP-MVPN] for this purpose.

   Once a PE decides to bind a set of VPLSes or customer multicast
   groups to an Inclusive P-Multicast tree or a Selective P-Multicast
   tree, it needs to announce this binding to other PEs in the network.
   This procedure is referred to as Inclusive P-Multicast tree or
   Selective P-Multicast tree binding distribution and is performed
   using BGP.

   When an Aggregated Inclusive P-Multicast tree is used by an ingress
   PE, this discovery implies that an ingress PE MUST announce the
   binding of all VPLSes bound to the Inclusive P-Multicast tree to the
   other PEs. The inner label assigned by the ingress PE for each VPLS
   MUST be included, if more than one VPLS is bound to the same P-
   Multicast tree. The Inclusive P-Multicast tree Identifier MUST be
   included.

   For a Selective P-Multicast tree this discovery implies announcing
   all the specific <C-S, C-G> entries bound to this P-Multicast tree
   along with the Selective P-Multicast tree Identifier. The inner label
   assigned for each <C-S, C-G> MUST be included if <C-S, C-G>s from
   different VPLSes are bound to the same P-Multicast tree. The labels
   MUST be distinct on a per VPLS basis and MAY be distinct on a per <C-
   S, C-G> basis.  The Selective P-Multicast 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 P-Multicast tree is termed 'Aggregation'. Both
   Inclusive and Selective P-Multicast trees support aggregation.

   Aggregation enables the SP to place a bound on the amount of
   multicast tree forwarding and control plane state which the P routers
   must have.  Let us call the number of VPLSes aggregated onto a single
   P-Multicast tree as the "Aggregation Factor". When Inclusive source
   P-Multicast trees are used the number of trees that a PE is the root



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   of is proportional to:

     + (Number of VPLSes on the PE / Aggregation Factor).


   In this case the state maintained by a P router, is proportional to:

     + ((Average number of VPLSes on a PE / Aggregation Factor) * number
       of PEs) / (Average number of P-Multicast trees that transit a
       given P router)


   Thus, the state does not grow linearly with the number of VPLSes.

   Aggregation requires a mechanism for the egresses of the P-Multicast
   tree to demultiplex the multicast traffic received over the P-
   Multicast tree.  To enable the egress nodes to perform this
   demultiplexing, upstream-assigned labels [RFC5331] MUST be assigned
   and distributed by the root of the aggregate P-multicast tree."


6.6. Inter-AS VPLS Multicast

   This document supports three models of inter-AS VPLS service, option
   (a), (b) and (c) which are very similar conceptually to option (a),
   (b) and (c) specified in [RFC4364] for IP VPNs. The three options
   described here are also similar to the three options described in in
   [RFC4761], which in turn extends the concepts of [RFC4364] to inter-
   AS VPLS.

   For option (a) and option (b) support 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 and they are described in section 10.

   For option (c) support this document specifies a model where Inter-AS
   VPLS service is offered by requiring a single P-Multicast tree to
   span multiple ASs. This is because in the case of option (c) the
   ASBRs do not exchange BGP-VPLS NLRIs or A-D routes.












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7. Intra-AS Inclusive P-Multicast Tree A-D/Binding

   This section specifies procedures for the intra-AS auto-discovery (A-
   D) 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 10.

   VPLS auto-discovery using BGP as described in [RFC4761, RFC6074]
   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. The NLRI defined in [RFC6074] 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 A-D NLRI to carry only
   the <RD, VE-ID>. Hence these procedures can be used for both BGP-VPLS
   and LDP-VPLS with BGP A-D.

   It is to be noted that BGP A-D is an inherent feature of BGP-VPLS.
   However it is not an inherent feature of LDP-VPLS. Infact there are
   deployments and/or implementations of LDP-VPLS that require
   configuration to enable a PE in a particular VPLS to determine other
   PEs in the VPLS and exchange PW labels using FEC 128 [RFC4447]. The
   use of BGP A-D for LDP-VPLS [RFC6074], to enable automatic setup of
   PWs, requires FEC 129 [RFC4447]. However FEC 129 is not required in
   order to use procedures in this document for LDP-VPLS.  An LDP-VPLS
   implementation that supports this document MUST support the BGP A-D
   procedures to setup P-Multicast trees, as described here, and it MAY
   support FEC 129 to automate the signaling of PWs.












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7.1. Originating intra-AS VPLS 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 BGP VPLS intra-AS auto-
   discovery route and advertises this route in Multi-Protocol (MP) I-
   BGP. The route is constructed as described in [RFC4761] and
   [RFC6074].

   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.

   The route also carries one or more Rout Targets (RTs) as specified in
   [RFC4761] and [RFC6074].

   If an Inclusive P-Multicast tree is used to instantiate the provider
   tunnel for VPLS multicast on the PE, the advertising PE MUST
   advertise the type and the identity of the P-Multicast tree in the
   the PMSI Tunnel attribute [BGP-MVPN]. This attribute is described in
   section 12.1.

   A PE that uses an Inclusive P-Multicast tree to instantiate the
   provider tunnel MAY aggregate two or more VPLSes present on the PE
   onto the same tree. If the PE decides to perform aggregation after it
   has already advertised the intra-AS VPLS auto-discovery routes for
   these VPLSes, 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 PMSI Tunnel attribute. If the PE has not
   previously advertised intra-AS auto-discovery routes for these
   VPLSes, then the aggregation requires the PE to advertise (new)
   intra-AS auto-discovery routes for these VPLSes.  The PMSI attribute
   in the newly advertised/re-advertised routes MUST carry the identity
   of the P-Multicast tree that aggregates the VPLSes, as well as an
   MPLS upstream-assigned label [RFC5331]. 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.











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7.2. Receiving intra-AS VPLS auto-discovery routes

   When a PE receives a BGP Update message that carries an intra-AS A-D
   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 PMSI Tunnel
   attribute, the PE performs the following.

   If the route carries the PMSI Tunnel attribute then:

     + If the Tunnel Type in the PMSI Tunnel attribute is set to LDP
       P2MP LSP, the PE SHOULD join the P-Multicast tree whose identity
       is carried in the PMSI Tunnel attribute.

     + If the Tunnel Type in the PMSI 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 PMSI Tunnel attribute does not carry a label, then all
       packets that are received on the P-Multicast tree, as identified
       by the PMSI Tunnel attribute, are forwarded using the VSIs that
       have at least one of its import Route Targets that matches one of
       the Route Targets of the received auto-discovery route.

     + If the PMSI 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 PMSI Tunnel attribute, with that upstream
       label are forwarded using the VSIs that have at least one of its
       import Route Target that matches one of the Route Targets of the
       received intra-AS auto-discovery route.


   If the local PE uses RSVP-TE P2MP LSP for sending (multicast)
   traffic, originated by VPLS sites connected to the PE, to the sites
   attached to other PEs then the local PE MUST use the Originating
   Router's IP address information carried in the intra-AS A-D route to
   add the PE, that originated the route, as a leaf node to the LSP.
   This MUST be done irrespective of whether the received Intra-AS A-D
   route carries the PMSI Tunnel attribute or not.




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8. Demultiplexing P-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. It also
   requires the egress PE to determine the identity of the ingress PE
   for MAC learning, as described in section 15.


8.1. One P-Multicast Tree - One VPLS Mapping

   When a P-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,
   e.g.,: RSVP-TE P2MP LSPs, the outer MPLS label is used to determine
   the tree. Penultimate-hop-popping MUST be disabled on the MPLS LSP
   (RSVP-TE P2MP LSP or LDP P2MP LSP).


8.2. One P-Multicast Tree - Many VPLS Mapping

   As traffic belonging to multiple VPLSes 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 determines 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 traffic from multiple VPLSes is carried on a single tree,
   upstream-assigned labels [RFC5331] MUST be used. Hence the inner
   label is assigned by the ingress PE.  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 MUST be used by
   the egress PE for all P-Multicast trees that have the same root
   [RFC5331].

   If the tree uses MPLS encapsulation, as in RSVP-TE P2MP LSPs, the
   outer MPLS label and optionally the incoming interface provides the
   label space of the label beneath it. This assumes that penultimate-
   hop-popping is disabled. The egress PE MUST NOT advertise IMPLICIT
   NULL or EXPLICIT NULL for that tree once its known to the egress PE
   that the tree is bound to one or more VPLSes. Once the label
   representing the tree is popped off the MPLS label stack, the next
   label is the demultiplexing information that allows the proper VPLS



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   instance to be determined.

   The ingress PE informs the egress PEs about the inner label as part
   of the tree binding procedures described in section 12.


9. Establishing P-Multicast Trees

   This document supports only P2MP P-Multicast trees wherein its
   possible for egress PEs to identify the ingress PE to perform MAC
   learning.  Specific procedures are specified only for RSVP-TE P2MP
   LSPs and LDP P2MP LSPs. An implementation that supports this document
   MUST support RSVP-TE P2MP LSPs and LDP P2MP LSPs.

   A P2MP tree is used to carry traffic originated in sites connected to
   the PE which is the root of the tree. These sites MAY belong to
   different VPLSes or the same VPLS.


9.1. Common Procedures

   The following procedures apply to both RSVP-TE P2MP and LDP P2MP
   LSPs.

   Demultiplexing the C-multicast data packets at the egress PE requires
   that the PE must be able to determine the P2MP LSP that the packets
   are received on. This enables the egress PE to determine the VPLS
   instances that the packet belongs to. To achieve this the LSP MUST be
   signaled with penultimate-hop-popping (PHP) off and a non-reserved
   MPLS label off as described in section 8. In other words an egress PE
   MUST NOT advertise IMPLICIT NULL or EXPLICIT NULL for a P2MP LSP that
   is carrying traffic for one or more VPLSes. 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 also needs to identify the ingress PE to perform MAC
   learning.  When P2MP LSPs are used as P2MP trees, determining the
   P2MP LSP that the packets are received on, is sufficient to determine
   the ingress PE.  This is because the ingress PE is the root of the
   P2MP LSP.

   The egress PE relies on receiving the PMSI Tunnel attribute in BGP to
   determine the VPLS instance to P2MP LSP mapping.







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9.2. RSVP-TE P2MP LSPs

   This section describes procedures that are specific to the usage of
   RSVP-TE P2MP LSPs for instantiating a P-Multicast tree. Procedures in
   [RFC4875] are used to signal the P2MP LSP. The LSP is signaled as the
   root of the P2MP LSP discovers the leaves. The egress PEs are
   discovered using the procedures described in section 7. Aggregation
   as described in this document is supported.


9.2.1. 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 12.1.

   Once the egress PE receives the P2MP TE LSP to VPLS 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.

       Note that if the signaling to set up an RSVP-TE P2MP LSP is
       completed before a given egress PE learns, via a PMSI Tunnel
       attribute, of the VPLS or set of VPLSes to which the LSP is
       bound, the PE MUST discard any traffic received on that LSP until
       the binding is received. In order for the egress PE to be able to
       discard such traffic it needs to know that the LSP is associated
       with one or more VPLSes and that the VPLS A-D route that binds
       the LSP to a VPLS has not yet been received. This is provided by
       extending [RFC4875] with [RSVP-OBB].





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9.3. Receiver Initiated MPLS Trees

   Receiver initiated P2MP MPLS trees signaled using LDP [mLDP] can also
   be used.  Procedures in [MLDP] MUST be used to signal the P2MP LSP.
   The LSP is signaled once the leaves receive the LDP FEC for the tree
   from the root as described in section 7. An ingress PE is required to
   discover the egress PEs when aggregation is used and this is achieved
   using the procedures in section 7.


9.3.1. 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 SHOULD "join" the P2MP MPLS tree by sending LDP label
   mapping messages for the LDP P2MP FEC, that was learned in the BGP
   advertisement, using procedures described in [MLDP].


9.4. Encapsulation of Aggregate P-Multicast Trees

   An Aggregate Inclusive P-Multicast tree or an Aggregate Selective P-
   Multicast tree MUST use a MPLS encapsulation. The protocol type in
   the data link header is as described in [RFC5332].


10. Inter-AS Inclusive P-Multicast Tree A-D/Binding

   This document supports four options of inter-AS VPLS service, option
   (a), (b), (c) and (e). Of these option (a), (b) and (c) are very
   similar conceptually to option (a), (b) and (c) specified in
   [RFC4364] for IP VPNs. These three options are also similar to the
   three options described in [RFC4761], which in turn extend the
   concepts of [RFC4364] to inter-AS VPLS. An implementation MUST
   support all three of these options. When there are multiple ways for
   implementing one of these options this section specifies which one is
   mandatory.

   For option (a), (b) and (e) support this section specifies a model
   where inter-AS VPLS service can be offered without requiring a single
   P-Multicast tree to span multiple ASes. This allows individual ASes



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   to potentially use different P-tunneling technologies. There are two
   variants of this model. One that requires MAC lookup on the ASBRs and
   applies to option (a) and (e). The other is one that does not require
   MAC lookup on the ASBRs and instead builds segmented inter-AS
   Inclusive or Selective trees.  This applies only to option (b).

   For option (c) support this document specifies a model where Inter-AS
   VPLS service is offered by requiring a single Inclusive P-Multicast
   tree to span multiple ASs. This is referred to as a non-segmented P-
   Multicast tree. This is because in the case of option (c) the ASBRs
   do not exchange BGP-VPLS NLRIs or VPLS A-D routes. Selective inter-AS
   trees for option (c) support may be segmented or non-segmented.


10.1. VSIs on the ASBRs

   When VSIs are configured on ASBRs, the ASBRs MUST perform a MAC
   lookup, in addition to any MPLS lookups, to determine the forwarding
   decision on a VPLS packet. The P-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 MUST be configured
   with its own VE ID for the VPLS. The BGP VPLS A-D routes generated by
   PEs in an AS MUST NOT be propagated outside the AS.


10.1.1. Option (a): VSIs on the ASBRs

   When VSIs are configured on ASBRs and option (a) is used then an ASBR
   in one AS treats an adjoining ASBR in another AS as a CE and
   determines the VSI for packets received from that ASBR based on the
   incoming ethernet interface.  In option (a) the ASBRs do not exchange
   VPLS A-D routes.

   An implementation MUST support option (a).


10.1.2. Option (e): VSIs on the ASBRs

   The VSIs on the ASBRs scheme can be used such that the interconnect
   between the ASBRs is a PW and MPLS encapsulation is used between the
   ASBRs.  An ASBR in one AS treats an adjoining ASBR in another AS as a
   CE and determines the VSI for packets received from another ASBR
   based on the incoming MPLS encapsulation. This is referred to as
   option (e).  The only VPLS A-D routes that are propagated outside the
   AS are the ones originated by ASBRs.  This MPLS PW connects the VSIs
   on the ASBRs and MUST be signaled using the procedures defined in
   [RFC4761] or [RFC4762].



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   The P-Multicast trees for a VPLS are confined to each AS and the VPLS
   auto-discovery/binding MUST follow the intra-AS procedures described
   in section 8. An implementation MAY support option (e).


10.2. Option (b) - Segmented Inter-AS Trees

   In this model, an inter-AS P-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 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 model, an ASBR is not required to keep 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. This model is applicable to option (b). An
   implementation MUST support option (b) using this model.

   The construction of segmented Inter-AS trees requires the BGP-VPLS A-
   D NLRI described in [RFC4761, RFC6074]. A BGP VPLS A-D 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 VPLS auto-discovery
   route (Though this route is originated by a PE as an intra-AS route
   and is referred to as an inter-AS route outside the AS).

   In addition to this, segmented inter-AS trees require support for the
   PMSI Tunnel attribute described in section 12.1. They also require
   additional procedures in BGP to signal leaf A-D routes between ASBRs
   as explained in subsequent sections.


10.2.1. Segmented Inter-AS Trees VPLS Inter-AS A-D/Binding

   This section specifies the procedures for inter-AS VPLS A-D/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. Note that instead of being
       configured, the ASBR MAY obtain this set of (import) Route
       Targets (RTs) by using Route Target Constrain [RFC4684].







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     + 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 PMSI Tunnel attribute for these tunnel types. Note that
       instead of being configured, the ASBR MAY derive the tunnel types
       from the intra-AS auto-discovery routes received by the ASBR from
       the PEs in its own AS.



   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.


10.2.2. Propagating BGP VPLS A-D 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.

   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



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   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 and a given AS there MUST be only one ASBR
   within that AS that accepts traffic flowing on that tree. Further for
   a given inter-AS tree and a given AS there MUST be only one ASBR in
   that AS that sends the traffic flowing on that tree to a particular
   adjacent AS.  The precise rules for accomplishing this are given in
   subsequent sections.

   An ASBR initiates creation of an intra-AS segment when the ASBR
   receives an inter-AS auto-discovery route from an E-BGP neighbor.
   Creation of the segment is completed as a result of distributing, via
   I-BGP, 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 VPLSes
   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 A-D routes received from other
   PEs in the AS, for the same VPLS (i.e. same VE-ID) as the one that
   the segment belongs to.

   The following sections specify procedures for propagation of inter-AS
   auto-discovery routes across ASes in order to construct inter-AS
   segmented trees.


10.2.2.1. Propagating Intra-AS VPLS A-D routes in E-BGP

   For a given VPLS configured on an ASBR when the ASBR receives intra-
   AS A-D routes originated by PEs in its own AS, the ASBR MUST
   propagate each of these route in E-BGP. This procedure MUST be
   performed for each of the VPLSes configured on the ASBR. Each of
   these routes is constructed as follows:



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     + The route carries a single BGP VPLS A-D NLRI with the RD and VE
       ID being the same as the NLRI in the received intra-AS A-D route.

     + The Next Hop field of the MP_REACH_NLRI attribute is set to a
       routable IP address of the ASBR.

     + The route carries the PMSI 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.


10.2.2.2. Inter-AS A-D route received via E-BGP

   When an ASBR receives from one of its E-BGP 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 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 inter-AS 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 in an AS pick the same route as the best
   route.  The best route selection procedures are specified in
   [RFC4761] and clarified in [MULTI-HOMING]. The best route procedures
   ensure that if multiple ASBRs, in an AS, receive the same inter-AS A-
   D route from their E-BGP neighbors, only one of these ASBRs
   propagates this route in I-BGP. This ASBR becomes the root of the
   intra-AS segment of the inter-AS tree and ensures that this is the
   only ASBR that accepts traffic into this AS from the inter-AS tree.

   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 tunnel used to instantiate the
   intra-AS segment of the inter-AS tunnel, the PMSI 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 MUST NOT
       carry the PMSI Tunnel attribute.

     + 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



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       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 VPLSes
       present on the ASBR onto the same tree. If the ASBR already
       advertises inter-AS auto-discovery routes for these VPLSes, then
       aggregation requires the ASBR to re-advertise these routes. The
       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
       VPLSes, then the aggregation requires the ASBR to advertise (new)
       inter-AS auto-discovery routes for these VPLSes. The PMSI Tunnel
       attribute in the newly advertised/re-advertised routes MUST carry
       the identity of the P-Multicast tree that aggregates the VPLSes,
       as well as an MPLS upstream-assigned label [RFC5331].  Each re-
       advertised route MUST have a distinct label.


   In addition the ASBR MUST send to the E-BGP 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 is described in section 12. 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 A-D NLRI of the inter-AS
       auto-discovery route received from the E-BGP 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 PMSI Tunnel
       attribute with the Tunnel Type set to Ingress Replication, and
       the Tunnel Identifier set to a routable address of the
       advertising router. The PMSI 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.







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     + To constrain the distribution scope of this route the route MUST
       carry the NO_ADVERTISE BGP community ([RFC1997]).

     + The ASBR constructs an IP-based Route Target extended community
       by placing the IP address carried in the next hop of the received
       Inter-AS VPLS A-D route in the Global Administrator field of the
       community, with the Local Administrator field of this community
       set to 0, and sets the Extended Communities attribute of the Leaf
       A-D route to that community. Note that this Route Target is the
       same as the ASBR Import RT of the EBGP neighbor from which the
       ASBR received the inter-AS VPLS A-D route.


10.2.2.3. Leaf A-D Route received via E-BGP

   When an ASBR receives via E-BGP a leaf auto-discovery route, the ASBR
   accepts the route only 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.

   If the ASBR accepts the leaf auto-discovery route, the ASBR finds an
   existing auto-discovery route whose BGP-VPLS A-D NLRI has the same
   value as the <RD, VE-ID> field of the leaf auto-discovery route.

   The MPLS label carried in the PMSI 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.


10.2.2.4. Inter-AS A-D Route received via I-BGP

   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 I-BGP 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. The best route determination is based as
   described in [RFC4761] and clarified in [MULTI-HOMING].



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   If the router is an ASBR then the ASBR propagates the route to its E-
   BGP neighbors. When propagating the route to the E-BGP 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 PMSI 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
   PMSI Tunnel attribute.

   If the received inter-AS auto-discovery route carries the PMSI 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 PMSI 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
   tree, as identified by the PMSI 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 PMSI 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.


10.3. Option (c): Non-Segmented Tunnels

   In this model. there is a multi-hop E-BGP peering between the PEs (or
   a Route Reflector) in one AS and the PEs (or Route Reflector) in
   another AS. The PEs exchange BGP-VPLS NLRI or BGP-VPLS A-D NLRI,
   along with PMSI Tunnel attribute, as in the intra-AS case described
   in section 8. An implementation MUST support this model.

   The PEs in different ASs use a non-segmented inter-AS P2MP tunnel for
   VPLS multicast. A non-segmented inter-AS tunnel is a single tunnel
   which spans AS boundaries. The tunnel technology cannot change from
   one point in the tunnel to the next, so all ASes through which the
   tunnel passes must support that technology. In essence, AS boundaries
   are of no significance to a non-segmented inter-AS P2MP tunnel.




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   This model requires no VPLS A-D routes in the control or VPLS MAC
   address learning in the data plane on the ASBRs. The ASBRs only need
   to participate in the non-segmented P2MP tunnel setup in the control
   plane, and do MPLS label forwarding in the data plane.

   The setup of non-segmented inter-AS P2MP tunnels MAY require the P-
   routers in one AS to have IP reachability to the loopback addresses
   of the PE routers in another AS, depending on the tunneling
   technology chosen. If this is the case, reachability to the loopback
   addresses of PE routers in one AS MUST be present in the IGP in
   another AS.

   The data forwarding in this model is the same as in the intra-AS case
   described in section 8.


11. Optimizing Multicast Distribution via Selective Trees

   Whenever a particular multicast stream is being sent on an Inclusive
   P-Multicast tree, it is likely that the data of that stream is being
   sent to PEs that do not require it as the sites connected to these
   PEs may have no receivers for the stream. If a particular stream has
   a significant amount of traffic, it may be beneficial to move it to a
   Selective P-Multicast tree which has at its leaves only those PEs,
   connected to sites that have receivers for the multicast stream (or
   at least includes fewer PEs that are attached to sites with no
   receivers compared to an Inclusive tree).

   A PE connected to the multicast source of a particular multicast
   stream may be performing explicit tracking i.e. it may know the PEs
   that have receivers in the multicast stream. Section 11.3 describes
   procedures that enable explicit tracking. If this is the case
   Selective P-Multicast trees can also be triggered on other criteria.
   For instance there could be a "pseudo wasted bandwidth" criteria:
   switching to a Selective tree would be done if the bandwidth
   multiplied by the number of uninterested PEs (PE that are receiving
   the stream but have no receivers) is above a specified threshold. The
   motivation is that (a) the total bandwidth wasted by many sparsely
   subscribed low-bandwidth groups may be large, and (b) there's no
   point to moving a high-bandwidth group to a Selective tree if all the
   PEs have receivers for it.

   Switching a (C-S, C-G) stream to a Selective P-Multicast tree may
   require the root of the tree to determine the egress PEs that need to
   receive the (C-S, C-G) traffic. This is true in the following cases:






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     + If the tunnel is a P2MP tree, such as a RSVP-TE P2MP Tunnel, the
       PE needs to know the leaves of the tree before it can instantiate
       the Selective tree.

     + If a PE decides to send traffic for multicast streams, belonging
       to different VPLSes, using one P-Multicast Selective tree, such a
       tree is termed an Aggregate tree with a selective mapping. The
       setting up of such an Aggregate tree requires the ingress PE to
       know all the other PEs that have receivers for multicast groups
       that are mapped onto the tree.

     + If ingress replication is used and the ingress PE wants to send
       traffic for (C-S, C-G)s to only those PEs that are on the path to
       receivers to the (C-S,C-G)s.


   For discovering the IP multicast group membership, for the above
   cases, this document describes procedures that allow an ingress PE to
   enable explicit tracking. Thus an ingress PE can request the IP
   multicast membership from egress PEs for one or more C-multicast
   streams. These procedures are described in section 11.3.

   The root of the Selective P-Multicast tree MAY decide to do explicit
   tracking of the IP multicast stream only after it has determined to
   move the stream to a Selective tree, or it MAY have been doing
   explicit tracking all along.  This document also describes explicit
   tracking for a wild-card source and/or group in section 11.3, which
   facilitates a Selective P-Multicast tree only mode in which IP
   multicast streams are always carried on a Selective P-Multicast tree.
   In the description on Selective P-Multicast trees the notation C-S,
   is intended to representeither a specific source address or a
   wildcard. Similarly C-G is intended to represent either a specific
   group address or a wildcard.

   The PE at the root of the tree MUST signal the leaves of the tree
   that the (C-S, C-G) stream is now bound to the to the Selective Tree.
   Note that the PE could create the identity of the P-Multicast tree
   prior to the actual instantiation of the tunnel.

   If the Selective tree is instantiated by a RSVP-TE P2MP LSP the PE at
   the root of the tree MUST establish the P2MP RSVP-TE LSP to the
   leaves. This LSP MAY have been established before the leaves receive
   the Selective tree binding, or MAY be established after the leaves
   receives the binding. A leaf MUST not switch to the Selective tree
   until it receives the binding and the RSVP-TE P2MP LSP is setup to
   the leaf.





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11.1. Protocol for Switching to Selective Trees

   Selective trees provide a PE the ability to create separate P-
   Multicast trees for certain <C-S, C-G> streams. The source PE, that
   originates the Selective tree, and the egress PEs, MUST use the
   Selective tree for the <C-S, C-G> streams that are mapped to it. This
   may require the source and egress PEs to switch to the Selective tree
   from an Inclusive tree if they were already using an Inclusive tree
   for the <C-S, C-G> streams mapped to the Selective tree.

   Once a source PE decides to setup an Selective tree, it MUST announce
   the mapping of the <C-S, C-G> streams (which may be in different
   VPLSes) that are mapped to the tree to the other PEs using BGP. 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> streams mapped to the
   tree. Setting up the forwarding path requires setting up the
   demultiplexing forwarding entries based on the top MPLS label (if
   there is no inner label) or the inner label (if present) as described
   in section 9. 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, after receiving the
   advertisement, when the P2MP LSP protocol is mLDP.  When the P2MP LSP
   protocol is P2MP RSVP-TE an egress PE MUST perform this switch to the
   Selective tree only after the advertisement from the ingress PE is
   received and the RSVP-TE P2MP LSP has been setup to the egress PE.
   This switch MAY be done after waiting for a preconfigured timer after
   these two steps have been accomplished.

   A source PE MUST use the following approach to decide when to start
   transmitting data on the Selective tree, if it was already using an
   Inclusive tree. A certain pre-configured delay after advertising the
   <C-S, C-G> streams 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> streams, that are mapped on the Selective
   tree, on the Inclusive tree. This traffic is instead transmitted on
   the Selective tree.


11.2. Advertising C-(S, G) Binding to a Selective Tree

   The ingress PE informs all the PEs that are on the path to receivers
   of the (C-S, C-G) of the binding of the Selective tree to the (C-S,
   C-G), using BGP. The BGP announcement is done by sending update for
   the MCAST-VPLS address family using what is referred to as the S-PMSI
   A-D route. The format of the NLRI is described in section 12.1. The
   NLRI MUST be constructed as follows:




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     +  The RD MUST be set to the RD configured locally for the VPLS.
       This is required to uniquely identify the <C-S, C-G> as the
       addresses could overlap between different VPLSes.  This MUST be
       the same RD value used in the VPLS auto-discovery process.

     +  The Multicast Source field MUST contain the source address
       associated with the C-multicast stream, and the Multicast Source
       Length field is set appropriately to reflect this. If the source
       address is a wildcard the source address is set to 0.

     +  The Multicast Group field MUST contain the group address
       associated with the C-multicast stream, and the Multicast Group
       Length field is set appropriately to reflect this. If the group
       address is a wildcard the group address is set to 0.

     + The Originating Router's IP Address field MUST be set to the IP
       address that the (local) PE places in the BGP next-hop of the
       BGP-VPLS A-D routes. Note that the <RD, Originating Router's IP
       address> tuple uniquely identifies a given VPLS.


   The PE constructs the rest of the Selective A-D route as follows.

   Depending on the type of a P-Multicast tree used for the P-tunnel,
   the PMSI tunnel attribute of the S-PMSI A-D route is constructed as
   follows:

     +  The PMSI tunnel attribute MUST contain the identity of the P-
       Multicast tree (note that the PE could create the identity of the
       tree prior to the actual instantiation of the tree).

     +  If in order to establish the P-Multicast tree the PE needs to
       know the leaves of the tree within its own AS, then the PE
       obtains this information from the Leaf A-D routes received from
       other PEs/ASBRs within its own AS (as other PEs/ASBRs originate
       Leaf A-D routes in response to receiving the S-PMSI A-D route) by
       setting the Leaf Information Required flag in the PMSI Tunnel
       attribute to 1. This enables explicit tracking for the multicast
       stream(s) advertised by the S-PMSI A-D route.

     +  If a PE originates S-PMSI A-D routes with the Leaf Information
       Required flag in the PMSI Tunnel attribute set to 1, then the PE
       MUST be (auto)configured with an import Route Target, which
       controls acceptance of Leaf A-D routes by the PE. (Procedures for
       originating Leaf A-D routes by the PEs that receive the S-PMSI A-
       D route are described in section "Receiving S-PMSI A-D routes by
       PEs.)




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       This Route Target is IP address specific. The Global
       Administrator field of this Route Target MUST be set to the IP
       address carried in the Next Hop of all the S-PMSI A-D routes
       advertised by this PE (if the PE uses different Next Hops, then
       the PE MUST be (auto)configured with multiple import RTs, one per
       each such Next Hop). The Local Administrator field of this Route
       Target MUST be set to 0.

       If the PE supports Route Target Constrain [RFC4684], the PE
       SHOULD advertise this import Route Target within its own AS using
       Route Target Constrains. To constrain distribution of the Route
       Target Constrain routes to the AS of the advertising PE these
       routes SHOULD carry the NO_EXPORT Community ([RFC1997]).

     +  A PE MAY aggregate two or more S-PMSIs originated by the PE onto
       the same P-Multicast tree. If the PE already advertises S-PMSI A-
       D routes for these S-PMSIs, 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 PMSI tunnel attribute.
       If the PE has not previously advertised S-PMSI A-D routes for
       these S-PMSIs, then the aggregation requires the PE to advertise
       (new) S-PMSI A-D routes for these S-PMSIs.  The PMSI Tunnel
       attribute in the newly advertised/re-advertised routes MUST carry
       the identity of the P-Multicast tree that aggregates the S-PMSIs.
       If at least some of the S-PMSIs aggregated onto the same P-
       Multicast tree belong to different VPLSes, then all these routes
       MUST carry an MPLS upstream assigned label [RFC5331].  If all
       these aggregated S-PMSIs belong to the same VPLS, then the routes
       MAY carry an MPLS upstream assigned label [RFC5331].  The labels
       MUST be distinct on a per VPLS basis, and MAY be distinct on a
       per route basis.


   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.

   By default the set of Route Targets carried by the route MUST be the
   same as the Route Targets carried in the BGP-VPLS A-D route
   originated from the VSI. The default could be modified via
   configuration.










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11.3. Receiving S-PMSI A-D routes by PEs

   Consider a PE that receives an S-PMSI A-D route. If one or more of
   the VSIs on the PE have their import Route Targets that contain one
   or more of the Route Targets carried by the received S-PMSI A-D
   route, then for each such VSI the PE performs the following.

   Procedures for receiving an S-PMSI A-D route by a PE (both within and
   outside of the AS of the PE that originates the route) are the same
   as specified in Section "Inter-AS A-D route received via IBGP" except
   that (a) instead of Inter-AS I-PMSI A-D routes the procedures apply
   to S-PMSI A-D routes, and (b) the rules for determining whether the
   received S-PMSI A-D route is the best route to the destination
   carried in the NLRI of the route, are the same as BGP path selection
   rules and may be modified by policy, and (c) a PE performs procedures
   specified in that section only if in addition to the criteria
   specified in that section the following is true:

     +  If as a result of multicast state snooping on the PE-CE
       interfaces, the PE has snooped state for at least one multicast
       join that matches the multicast source and group advertised in
       the S-PMSI A-D route. Further if the oif (outgoing interfaces)
       for this state contains one or more interfaces to the locally
       attached CEs. When the multicast signaling protocol among the
       CEs is IGMP, then snooping and associated procedures are
       defined in [RFC 4541]. The snooped state is determined using
       these procedures. When the multicast signaling protocol among
       the CEs is PIM the, procedures in RFC4541 are not sufficient to
       determine the snooped state. The additional details required to
       determine the snooped state when CE-CE protocol is PIM are for
       further study. When such procedures are defined it is expected
       that the procedures in this section will apply to the snooped
       state created as a result of PIM as CE-CE protocol.


   The snooped state is said to "match" the S-PMSI A-D route if any of
   the following is true:

     +  The S-PMSI A-D route carries (C-S, C-G) and the snooped state is
       for (C-S, C-G). OR

     +  The S-PMSI A-D route carries (C-*, C-G) and (a) the snooped
       state is for (C-*, C-G) OR (b) the snooped state is for at least
       one multicast join with the multicast group address equal to C-G
       and there doesn't exist another S-PMSI A-D route that carries (C-
       S, C-G) where C-S is the source address of the snooped state.





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     +  The S-PMSI A-D route carries (C-S, C-*) and (a) the snooped
       state is for at least one multicast join with the multicast
       source address equal to C-S, and (b) there doesn't exist another
       S-PMSI A-D route that carries (C-S, C-G) where C-G is the group
       address of the snooped state.

     +  The S-PMSI A-D route carries (C-*, C-*) and there is no other S-
       PMSI A-D route that matches the snooped state as per the above
       conditions.


   Note if the above conditions are true, and if the received S-PMSI A-D
   route has a PMSI Tunnel attribute with the Leaf Information Required
   flag set to 1, then the PE originates a Leaf A-D route. The Route Key
   of the Leaf A-D route is set to the MCAST-VPLS NLRI of the S-PMSI A-D
   route. The rest of the Leaf A-D route is constructed using the same
   procedures as specified in section "Originating Leaf A-D route into
   IBGP", except that instead of originating Leaf A-D routes in response
   to receiving Inter-AS A-D routes the procedures apply to originating
   Leaf A-D routes in response to receiving S-PMSI A-D routes.

   In addition to the procedures specified in Section "Inter-AS A-D
   route received via IBGP" the PE MUST set up its forwarding path to
   receive traffic, for each multicast stream in the matching snooped
   state, from the tunnel advertised  by the S-PMSI A-D route (the PE
   MUST switch to the Selective tree).

   When a new snooped state is created by a PE then the PE MUST first
   determine if there is a S-PMSI route that matches the snooped state
   as per the conditions described above. If such a S-PMSI route is
   found then the PE MUST follow the procedures described in this
   section, for that particular S-PMSI route.


11.4. Inter-AS Selective Tree

   Inter-AS Selective trees support all three options of inter-AS VPLS
   service, option (a), (b) and (c), that are supported by Inter-AS
   Inclusive trees.  They are constructed in a manner that is very
   similar to Inter-AS Inclusive trees.

   For option (a) and option (b) support inter-AS Selective trees are
   constructed 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.
   One that requires MAC and IP multicast lookup on the ASBRs and
   another that does not require MAC/IP multicast lookup on the ASBRs
   and instead builds segmented inter-AS Selective trees.



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   Segmented Inter-AS Selective trees can also be used with option (c)
   unlike Segmented Inter-AS Inclusive trees. This is because the S-PMSI
   A-D routes can be exchanged via ASBRs (even though BGP VPLS A-D
   routes are not exchanged via ASBRs).

   In the case of Option (c) an Inter-AS Selective tree may also be a
   non-segmented P-Multicast tree that spans multiple ASs.


11.4.1. VSIs on the ASBRs

   The requirements on ASBRs, when VSIs are present on the ABSRs,
   include the requirements presented in section 10. The source ASBR
   (that receives traffic from another AS) may independently decide
   whether it wishes to use Selective trees or not. If it uses Selective
   trees the source ASBR MUST perform a MAC lookup to determine the
   Selective tree to forward the VPLS packet on.


11.4.1.1. VPLS Inter-AS Selective Tree A-D Binding

   The mechanisms for propagating S-PMSI A-D routes are the same as the
   intra-AS case described in section 12.2. The BGP Selective tree A-D
   routes generated by PEs in an AS MUST NOT be propagated outside the
   AS.


11.4.2. Inter-AS Segmented Selective Trees

   Inter-AS Segmented Selective trees MUST be used when option (b) is
   used to provide the inter-AS VPLS service. They MAY be used when
   option (c) is used to provide the inter-AS VPLS service.

   A Segmented inter-AS Selective Tunnel is constructed similar to an
   inter-AS Segmented Inclusive Tunnel. Namely, such a tunnel is
   constructed as a concatenation of tunnel segments. There are two
   types of tunnel segments: an intra-AS tunnel segment (a segment that
   spans ASBRs within the same AS), and inter-AS tunnel segment (a
   segment that spans adjacent ASBRs in adjacent ASes). ASes that are
   spanned by a tunnel are not required to use the same tunneling
   mechanism to construct the tunnel - each AS may pick up a tunneling
   mechanism to construct the intra-AS tunnel segment of the tunnel, in
   its AS.

   The PE that decides to set up a Selective tree, advertises the
   Selective tree to multicast stream binding using a S-PMSI A-D route
   as per procedures in section 11.2, to the routers in its own AS.




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   A S-PMSI A-D route advertised outside the AS, to which the
   originating PE belongs, will be referred to as an inter-AS Selective
   Tree A-D route (Although this route is originated by a PE as an
   intra-AS route it is referred to as an inter-AS route outside the
   AS).



11.4.2.1. Handling S-PMSI A-D routes by ASBRs

   Procedures for handling an S-PMSI A-D route by ASBRs (both within and
   outside of the AS of the PE that originates the route) are the same
   as specified in Section "Propagating VPLS BGP A-D routes to other
   ASes", except that instead of Inter-AS BGP-VPLS A-D routes and the
   BGP-VPLS A-D NLRI these procedures apply to S-PMSI A-D routes and the
   S-PMSI A-D NLRI.

   In addition to these procedures an ASBR advertises a Leaf A-D route
   in response to a S-PMSI A-D route only if:

     +  The S-PMSI A-D route was received via EBGP from another ASBR and
       the ASBR merges the S-PMSI A-D route into an Inter-AS BGP VPLS A-
       D route as described in the next section. OR

     +  The ASBR receives a Leaf A-D route from a downstream PE or ASBR
       in response to the S-PMSI A-D route, received from an upstream PE
       or ASBR, that the ASBR propagated inter-AS to downstream ASBRs
       and PEs.

     +  The ASBR has snooped state from local CEs that matches the NLRI
       carried in the S-PMSI A-D route as per the following rules:

       i) The NLRI encodes (C-S, C-G) which is the same as the snooped
       (C-S, C-G) ii) The NLRI encodes (*, C-G) and there is snooped
       state for at least one (C-S, C-G) and there is no other matching
       SPMSI A-D route for (C-S, C-G) OR there is snooped state for (*,
       C-G) iii) The NLRI encodes (*, *) and there is snooped state for
       at least one (C-S, C-G) or (*, C-G) and there is no other
       matching SPMSI A-D route for that (C-S, C-G) or (*, C-G)
       respecively.



   The C-multicast data traffic is sent on the Selective tree by the
   originating PE. When it reaches an ASBR that is on the Inter-AS
   segmented tree, it is delivered to local receivers, if any. It is
   then forwarded on any inter-AS or intra-AS segments that exist on the
   Inter-AS Selective Segmented tree. If the Inter-AS Segmented



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   Selective Tree is merged onto an Inclusive tree, as described in the
   next section, the data traffic is forwarded onto the Inclusive tree.



11.4.2.1.1. Merging Selective Tree into an Inclusive Tree

   Consider the situation where:

     +  An ASBR is receiving (or expecting to receive) inter-AS (C-S, C-
       G) data from upstream via a Selective tree.

     +  The ASBR is sending (or expecting  to send) the inter-AS  (C-S,
       C-G) data downstream via an Inclusive tree.


   This situation may arise if the upstream providers have a policy of
   using Selective trees but the downstream providers have a policy of
   using Inclusive trees. To support this  situation, an ASBR  MAY,
   under certain conditions, merge one or more upstream Selective trees
   into a downstream Inclusive tree. Note that this can be the case only
   for option (b) and not for option (c) as for option (c) the ASBRs do
   not have Inclusive tree state.

   A Selective tree (corresponding to a particular S-PMSI A-D route) MAY
   be merged by  a particular  ASBR into  an  Inclusive tree
   (corresponding  to a particular Inter-AS BGP VPLS A-D route) if and
   only if  the following conditions all hold:

     +  The S-PMSI A-D route and the Inter-AS BGP VPLS A-D route
       originate in the same AS. The Inter-AS BGP VPLS A-D route carries
       the originating AS in the AS_PATH attribute of the route. The S-
       PMSI A-D route carries the originating AS in the AS_PATH
       attribute of the route.

     +  The S-PMSI A-D route and the Inter-AS BGP VPLS A-D route have
       exactly the same set of RTs.


   An ASBR performs merging by stitching the tail end of the P-tunnel,
   as specified in the the PMSI Tunnel attribute of the S-PMSI A-D route
   received by the ASBR, to the to the head of the P-tunnel, as
   specified in the PMSI Tunnel attribute of the Inter-AS BGP VPLS A-D
   route re-advertised by the ASBR.

   An ASBR that merges an S-PMSI A-D route into an Inter-AS BGP VPLS A-D
   route MUST NOT re-advertise the S-PMSI A-D route.




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11.4.3. Inter-AS Non-Segmented Selective trees

   Inter-AS Non-segmented Selective trees MAY be used in the case of
   option (c).

   In this method, there is a multi-hop E-BGP peering between the PEs
   (or a Route Reflector) in one AS and the PEs (or Route Reflector) in
   another AS. The PEs exchange BGP Selective tree A-D routes, along
   with PMSI Tunnel attribute, as in the intra-AS case described in
   section 10.3.

   The PEs in different ASs use a non-segmented Selective inter-AS P2MP
   tunnel for VPLS multicast.

   This method requires no VPLS information (in either the control or
   the data plane) on the ASBRs. The ASBRs only need to participate in
   the non-segmented P2MP tunnel setup in the control plane, and do MPLS
   label forwarding in the data plane.

   The data forwarding in this model is the same as in the intra-AS case
   described in section 9.


12. BGP Extensions

   This section describes the encoding of the BGP extensions required by
   this document.


12.1. Inclusive Tree/Selective Tree Identifier

   Inclusive P-Multicast tree and Selective P-Multicast tree
   advertisements carry the P-Multicast tree identifier.

   This document reuses the BGP attribute, called PMSI Tunnel attribute
   that is defined in [BGP-MVPN].

   This document supports only the following Tunnel Types when PMSI
   Tunnel attribute is carried in VPLS A-D or VPLS S-PMSI A-D routes:

     + 0 - No tunnel information present
     + 1 - RSVP-TE P2MP LSP
     + 2 - LDP P2MP LSP
     + 6 - Ingress Replication







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12.2. MCAST-VPLS NLRI

   This document defines a new BGP NLRI, called the MCAST-VPLS NLRI.

   Following is the format of the MCAST-VPLS NLRI:

                +-----------------------------------+
                |    Route Type (1 octet)           |
                +-----------------------------------+
                |     Length (1 octet)              |
                +-----------------------------------+
                | Route Type specific (variable)    |
                +-----------------------------------+


   The Route Type field defines encoding of the rest of MCAST-VPLS NLRI
   (Route Type specific MCAST-VPLS NLRI).

   The Length field indicates the length in octets of the Route Type
   specific field of MCAST-VPLS NLRI.

   This document defines the following Route Types for auto-discovery
   routes:
     + 3 - Selective Tree auto-discovery route;
     + 4 - Leaf auto-discovery route.

   The MCAST-VPLS NLRI is carried in BGP using BGP Multiprotocol
   Extensions [RFC4760] with an AFI of 25 (L2VPN AFI), and an SAFI of
   MCAST-VPLS [To be assigned by IANA]. The NLRI field in the
   MP_REACH_NLRI/MP_UNREACH_NLRI attribute contains the MCAST-VPLS NLRI
   (encoded as specified above).

   In order for two BGP speakers to exchange labeled MCAST-VPLS NLRI,
   they must use BGP Capabilities Advertisement to ensure that they both
   are capable of properly processing such NLRI. This is done as
   specified in [RFC4760], by using capability code 1 (multiprotocol
   BGP) with an AFI of 25 and an SAFI of MCAST-VPLS.

   The following describes the format of the Route Type specific MCAST-
   VPLS NLRI for various Route Types defined in this document.


12.2.1. S-PMSI auto-discovery route

   An S-PMSI A-D route type specific MCAST-VPLS NLRI consists of the
   following:

                +-----------------------------------+



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                |      RD   (8 octets)              |
                +-----------------------------------+
                | Multicast Source Length (1 octet) |
                +-----------------------------------+
                |  Multicast Source (Variable)      |
                +-----------------------------------+
                |  Multicast Group Length (1 octet) |
                +-----------------------------------+
                |  Multicast Group   (Variable)     |
                +-----------------------------------+
                |   Originating Router's IP Addr    |
                +-----------------------------------+

   The RD is encoded as described in [RFC4364].

   The Multicast Source field contains the C-S address i.e the address
   of the multicast source. If the Multicast Source field contains an
   IPv4 address, then the value of the Multicast Source Length field is
   32.  If the Multicast Source field contains an IPv6 address, then the
   value of the Multicast Source Length field is 128. The value of the
   Multicast Source Length field may be set to 0 to indicate a wildcard.

   The Multicast Group field contains the C-G address i.e. the address
   of the multicast group. If the Multicast Group field contains an IPv4
   address, then the value of the Multicast Group Length field is 32.
   If the Multicast Group field contains an IPv6 address, then the value
   of the Multicast Group Length field is 128. The Multicast Group
   Length field may be set to 0 to indicate a wildcard.

   Whether the Originating Router's IP Address field carries an IPv4 or
   IPv6 address is determined from the value of the Length field of the
   MCAST-VPLS NLRI. If the Multicast Source field contains an IPv4
   address and the Multicast Group field contains an IPv4 address,  then
   the value of the Length field is 22 if the Originating Router's IP
   address carries an IPv4 address and 34 if it is an IPv6 address.  If
   the Multicast Source and Multicast Group fields contain IPv6
   addresses, then the value of the Length field is 46 if the
   Originating Router's IP address carries an IPv4 address and 58 if it
   is an IPv6 address.  The following table summarizes the above.


      Multicast   Multicast                Originating Router's   Length
      Source      Group                       IP Address

        IPv4      IPv4                        IPv4                  22
        IPv4      IPv4                        IPv6                  34
        IPv6      IPv6                        IPv4                  46
        IPv6      IPv6                        IPv6                  58



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   Usage of Selective Tree auto-discovery routes is described in Section
   11.


12.2.2. Leaf auto-discovery route

   A leaf auto-discovery route type specific MCAST-VPLS NLRI consists of
   the following:

                +-----------------------------------+
                |      Route Key (variable)         |
                +-----------------------------------+
                |   Originating Router's IP Addr    |
                +-----------------------------------+

   Whether the Originating Router's IP Address field carries an IPv4 or
   IPv6 address is determined from the Length field of the MCAST-VPLS
   NLRI and the length field of the Route Key. From these two length
   fields one can compute the length of the Originating Router's IP
   Address. If this computed length is 4 then the address is an IPv4
   address and if its 16 then the address is an IPv6 address.

   Usage of Leaf auto-discovery routes is described in sections "Inter-
   AS Inclusive P-Multicast tree A-D/Binding" and "Optimizing Multicast
   Distribution via Selective trees".


13. Aggregation Considerations

   In general the heuristic 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 VPLSes that are aggregated on the Aggregate
   Inclusive tree. If there is complete overlap aggregation is perfectly
   congruent. As the overlap between the VPLSes that are aggregated
   reduces, the congruency reduces.

   If aggregation is done such that it is not perfectly congruent a PE
   may receive traffic for VPLSes to which it doesn't belong. As the
   amount of multicast traffic in these unwanted VPLSes increases
   aggregation becomes less optimal with respect to delivered traffic.
   Hence there is a tradeoff between reducing state and delivering
   unwanted traffic.



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   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 VPLSes 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.


14. Data Forwarding

14.1. MPLS Tree Encapsulation

14.1.1. Mapping multiple VPLS instances to a P2MP LSP

   The following diagram shows the progression of the VPLS 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



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   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 [RFC5331].

   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.


14.1.2. Mapping one VPLS instance to a P2MP LSP

   The following diagram shows the progression of the VPLS multicast
   packet as it enters and leaves the SP network when a given MPLS tree
   is being used for a single VPLS instance. 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|
      ++=============++       ++=============++       ++=============++
      ||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 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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15. VPLS Data Packet Treatment

   If the destination MAC address of a VPLS packet received by a PE from
   a VPLS site is a multicast address, a P-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 MUST be used. Else if a (C-*, C-*)
   Selective tree exisits for the VPLS it 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 a (C-*, C-*) Selective tree exists for the
   VPLS the PE SHOULD flood over it. Else if Inclusive tree exists for
   the VPLS the PE SHOULD flood over it.  Else the 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 P-Multicast trees or a Selective P-Multicast tree
   bound to (C-*, C-*) 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 P-Multicast tree.  This further implies that
   the MPLS P-Multicast tree technology MUST allow the egress PE to
   determine the sender PE from the received MPLS packet.

   When a receiver PE receives a VPLS packet with a source MAC address,
   that has not yet been learned, on a P-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 P-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 P-Multicast tree, this could lead to packet
   reordering. This constraint should be taken into consideration if
   unknown unicast frames are forwarded using a  P-Multicast tree,
   instead of multiple PWs based on [RFC4761] or [RFC4762].

   An implementation MUST support the ability to transport unknown
   unicast traffic over Inclusive P-Multicast trees. Further an
   implementation MUST support the ability to perform MAC address



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   learning for packets received on a P-Multicast tree.


16. Security Considerations

   Security considerations discussed in [RFC4761] and [RFC4762] apply to
   this document. This section describes additional considerations.

   As mentioned in [RFC4761], there are two aspects to achieving data
   privacy in a VPLS: securing the control plane and protecting the
   forwarding path. Compromise of the control plane could result in a PE
   sending multicast data belonging to some VPLS to another VPLS, or
   blackholing VPLS multicast data, or even sending it to an
   eavesdropper; none of which are acceptable from a data privacy point
   of view. The mechanisms in this document use BGP for the control
   plane. Hence techniques such as in [RFC2385] help authenticate BGP
   messages, making it harder to spoof updates (which can be used to
   divert VPLS traffic to the wrong VPLS) or withdraws (denial-of-
   service attacks).  In the multi-AS methods (b) and (c) described in
   Section 11, this also means protecting the inter-AS BGP sessions,
   between the ASBRs, the PEs, or the Route Reflectors.

   Note that [RFC2385] will not help in keeping MPLS labels, associated
   with P2MP LSPs or the upstream MPLS labels used for aggregation,
   private -- knowing the labels, one can eavesdrop on VPLS traffic.
   However, this requires access to the data path within a Service
   Provider network.

   One of the requirements for protecting the data plane is that the
   MPLS labels are accepted only from valid interfaces. This applies
   both to MPLS labels associated with P2MP LSPs and also applies to the
   upstream assigned MPLS labels. For a PE, valid interfaces comprise
   links from P routers. For an ASBR, valid interfaces comprise links
   from P routers and links from other ASBRs in ASes that have instances
   of a given VPLS. It is especially important in the case of multi-AS
   VPLSes that one accept VPLS packets only from valid interfaces.


17. IANA Considerations

   This document defines a new NLRI, called MCAST-VPLS, to be carried in
   BGP using multiprotocol extensions. It requires assignment of a new
   SAFI. This is to be assigned by IANA.

   This document defines a BGP optional transitive attribute, called
   PMSI attribute. This is the same attribute as the one defined in
   [BGP-MVPN] and the code point for this attribute has already been
   assigned by IANA as 22 [BGP-IANA]. Hence no further action is



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   required from IANA regarding this attribute.


18. Acknowledgments

   Many thanks to Thomas Morin for his support of this work. We would
   also like to thank authors of [BGP-MVPN] and [MVPN] as the details of
   the inter-AS segmented tree procedures in this document have
   benefited from those in [BGP-MVPN] and [MVPN]. We would also like to
   thank Wim Henderickx for his comments.


19. Normative References

   [RFC2119] "Key words for use in RFCs to Indicate Requirement
   Levels.", Bradner, March 1997

   [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

   [RFC4760] T. Bates, et. al., "Multiprotocol Extensions for BGP-4",
   January 2007

   [RFC5331] R. Aggarwal, Y. Rekhter, E. Rosen, "MPLS Upstream Label
   Assignment and Context Specific Label Space", RFC 5331, August 2008

   [RSVP-OBB]  Z. Ali, G. Swallow, R. Aggarwal, "Non PHP behavior and
   out-of-band mapping for RSVP-TE LSPs", draft-ietf-mpls-rsvp-te-no-
   php-obb-mapping, work in progress.


20. Informative References

   [RFC6074] E. Rosen et. al., "Provisioning, Autodiscovery, and
   Signaling in L2VPNs", RFC 6074

   [RFC5332] T. Eckert, E. Rosen, R. Aggarwal, Y. Rekhter, "MPLS
   Multicast Encapsulations", RFC 5332, August 2008

   [MVPN] E. Rosen, R. Aggarwal, "Multicast in 2547 VPNs", draft-ietf-
   l3vpn-2547bis-mcast-08.txt"

   [BGP-MVPN] R. Aggarwal, E. Rosen, Y. Rekhter, T. Morin, C.
   Kodeboniya.  "BGP Encodings for Multicast in 2547 VPNs", draft-ietf-
   l3vpn-2547bis-mcast-bgp-06.txt



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   [RFC4875] 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, work in progress.

   [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

   [RFC1997] R. Chandra, et. al., "BGP Communities Attribute", August
   1996

   [BGP-IANA] http://www.iana.org/assignments/bgp-parameters

   [RFC4684] P. Marques et. al., "Constrained Route Distribution for
   Border Gateway Protocol/MultiProtocol Label Switching (BGP/MPLS)
   Internet Protocol (IP) Virtual Private Networks (VPNs)", RFC 4684,
   November 2006

   [RFC2385] Heffernan, A., "Protection of BGP Sessions via the TCP MD5
   Signature Option", RFC 2385, August 1998.

   [RFC4447] L. Martini et. al., "Pseudowire Setup and Maintenance Using
   the Label Distribution Protocol (LDP)", RFC 4447 April 2006

   [MULTI-HOMING] K. Kompella et. al., "Multi-homing in BGP-based
   Virtual Private LAN Service", draft-kompella-l2vpn-vpls-
   multihoming-02.txt

   [IGMP-SN] M. Christensen et. al., "Considerations for Internet Group
   Management Protocol (IGMP) and Multicast Listener Discovery (MLD)
   Snooping Switches", RFC 4541, May 2006

   [RFC4601] B. Fenner, et. al., "PIM-SM Protocol Specification", RFC
   4601











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21. Author's Address

   Rahul Aggarwal

   998 Lucky Avenue
   Menlo Park, CA 94025

   Email: raggarwa_1@yahoo.com

   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
   Cisco Systems
   300 Beaver Brook Road
   BOXBOROUGH, MA 01719
   USA

   Email: lufang@cisco.com

   Yakov Rekhter
   Juniper Networks
   1194 North Mathilda Ave.
   Sunnyvale, CA 94089
   USA

   Email: yakov@juniper.net

   Chaitanya Kodeboniya















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