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Versions: (RFC 2547) 00 01 02 draft-ietf-l3vpn-2547bis-mcast-bgp

Network Working Group                                        R. Aggarwal
Internet Draft                                          Juniper Networks
Expiration Date: December 2006
                                                                E. Rosen
                                                     Cisco Systems, Inc.

                                                                T. Morin
                                                          France Telecom

                                                              Y. Rekhter
                                                        Juniper Networks

                                                           C. Kodeboniya


                                                               June 2006


            BGP Encodings for Multicast in MPLS/BGP IP VPNs


             draft-raggarwa-l3vpn-2547bis-mcast-bgp-02.txt

Status of this Memo

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Abstract

   This document describes the BGP encodings for signaling the
   information elements required by Multicast in MPLS/BGP IP VPNs, as
   specified in [MVPN].














































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Table of Contents

 1          Specification of requirements  .........................   4
 2          Terminology  ...........................................   4
 3          Introduction  ..........................................   5
 4          MCAST-VPN NLRI  ........................................   6
 4.1        Intra-AS I-PMSI auto-discovery route  ..................   7
 4.2        Inter-AS I-PMSI auto-discovery route  ..................   7
 4.3        S-PMSI auto-discovery route  ...........................   7
 4.4        Leaf auto-discovery route  .............................   8
 4.5        Source Active auto-discovery route (SA auto-discovery route)  9
 4.6        C-Multicast Route  .....................................   9
 5          P-Multicast Service Interface Tunnel (PMSI Tunnel) attribute  10
 6          Source AS Extended Community  ..........................  12
 7          Route Import Extended Community  .......................  13
 8          MVPN Auto-Discovery/Binding  ...........................  14
 8.1        MVPN Auto-Discovery/Binding - Intra-AS Operations  .....  14
 8.1.1      Originating (intra-AS) auto-discovery routes  ..........  14
 8.1.2      Receiving (intra-AS) auto-discovery routes  ............  16
 8.2        MVPN Auto-Discovery/Binding - Inter-AS Operations  .....  17
 8.2.1      Originating Inter-AS MVPN Auto-Discovery routes  .......  18
 8.2.2      Propagating Inter-AS MVPN Auto-Discovery routes  .......  19
 8.2.2.1    Inter-AS Auto-Discovery Route received via EBGP  .......  20
 8.2.2.2    Leaf Auto-Discovery Route received via EBGP  ...........  22
 8.2.2.3    Inter-AS Auto-Discovery Route received via IBGP  .......  22
 8.2.2.4    Leaf Auto-Discovery route received via IBGP  ...........  24
 9          Non-congruent Unicast and Multicast Connectivity  ......  25
10          VPN C-Multicast Routing Information Exchange among PEs ...26
10.1        Originating C-Multicast Routes by a PE  ................  26
10.1.1      Constructing MCAST-VPN NLRI  ...........................  26
10.1.1.1    PIM as the C-Multicast protocol  .......................  26
10.1.1.2    mLDP as the C-Multicast protocol  ......................  28
10.1.2      Constructing the rest of the C-multicast route  ........  29
10.1.3      Unicast Route Changes  .................................  29
10.2        Propagating C-Multicast routes by an ASBR  .............  29
10.3        Receiving C-Multicast Routes by a PE  ..................  31
10.3.1      PIM as the C-Multicast protocol  .......................  31
10.3.1.1    Source Tree Join C-Multicast route  ....................  31
10.3.1.2    Shared Tree Join C-Multicast route  ....................  31
10.3.1.3    Prune Source from Shared Tree C-Multicast route  .......  32
10.3.2      mLDP as the C-Multicast protocol  ......................  32
10.4        C-multicast Routes Aggregation  ........................  32
11          Switching to S-PMSI  ...................................  33
11.1        Originating S-PMSI auto-discovery routes  ..............  33



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12          Carrier's Carrier  .....................................  35
13          Choosing a single forwarder PE when switching from RPT to SPT  35
13.1        Source Within a Site - Source Active Advertisement  ....  35
13.2        Receiving Source Active auto-discovery route  ..........  36
14          Co-locating C-RPs on a PE  .............................  37
14.1        Source Within a Site - Source Active Advertisement  ....  37
14.2        Receiver(s) Within a Site  .............................  38
14.3        Receiving C-multicast routes  ..........................  39
15          Scalability Considerations  ............................  39
16          Dampening of C-multicast routes  .......................  41
16.1         Dampening of C-multicast prunes  ......................  41
16.2        Dampening of C-multicast joins  ........................  42
16.3        Dampening of leaf auto-discovery routes  ...............  42
17          IANA Consideration  ....................................  42
18          Security Considerations  ...............................  43
19          Acknowledgement  .......................................  43
20          References  ............................................  43
20.1        Normative References  ..................................  43
20.2        Informative References  ................................  43
21          Author Information  ....................................  44
22          Intellectual Property Statement  .......................  44
23            ......................................................  45






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. Terminology

   In the context of this document we will refer to the MVPN auto-
   discovery/binding information carried in BGP as "auto-discovery
   routes". For a given MVPN there are the following types of auto-
   discovery routes:

     + intra-AS auto-discovery route (auto-discovery route);

     + inter-AS auto-discovery route;






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     + S-PMSI auto-discovery route;

     + intra-AS segment leaf auto-discovery route (leaf auto-discovery
       route);

     + Source Active auto-discovery route (SA auto-discovery route).

   In the context of this document we will refer to the MVPN customers
   multicast routing information carried in BGP as "C-multicast routes".
   For a given MVPN there are the following types of C-multicast routes:

     + Shared Tree Join route;

     + Source Tree Join route;

     + Prune Source from Shared Tree route.

   For each MVPN present on a PE, the PE maintains a Tree Information
   Base (MVPN-TIB). This is the same as TIB defined in [PIM-SM], except
   that instead of a single TIB a PE maintains multiple MVPN-TIBs, one
   per each MVPN.


3. Introduction

   This document describes the BGP encodings for exchanging the
   information elements required by Multicast in MPLS/BGP IP VPNs, as
   specified in [MVPN]. This document assumes a thorough familiarity
   with procedures, concepts and terms described in [MVPN].

   This document defines a new NLRI, MCAST-VPN NLRI. The MCAST-VPN NLRI
   is used for MVPN auto-discovery, advertising MVPN - I-PMSI tunnel
   binding, advertising <C-S, C-G> - S-PMSI tunnel binding, VPN customer
   multicast routing information exchange among PEs, choosing a single
   forwarder PE, and for procedures in support of co-locating a C-RP on
   a PE.

   This document also specifies new BGP attribute, P-Multicast Service
   Interface Tunnel (PMSI Tunnel) attribute.












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4. MCAST-VPN NLRI

   This document defines a new BGP NLRI, called the MCAST-VPN NLRI.
   This NLRI is carried in BGP using BGP Multiprotocol Extensions
   [RFC2858].  Following is the format of the MCAST-VPN NLRI:

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


   The Length field indicates the length in octets of MCAST-VPN NLRI,
   excluding the Length field itself.

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

   This document defines the following Route Types for auto-discovery
   routes:

     + 1 - Intra-AS I-PMSI auto-discovery route (or just auto-discovery
       route);
     + 2 - Inter-AS I-PMSI auto-discovery route (or just inter-AS auto-
       discovery route);
     + 3 - S-PMSI auto-discovery route;
     + 4 - Intra-AS segment leaf auto-discovery route (or just leaf
       auto-discovery route).
     + 5 - Source Active auto-discovery route (or just SA auto-discovery
       route).

   This document defines the following Route Types for C-multicast
   routes:

     + 6 - Shared Tree Join route;
     + 7 - Source Tree Join route;
     + 8 - Prune Source from Shared Tree route.

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








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4.1. Intra-AS I-PMSI auto-discovery route

   An intra-AS I-PMSI auto-discovery route type specific MCAST-VPN NLRI
   consists of the following:

                +-----------------------------------+
                |      RD   (8 octets)              |
                +-----------------------------------+
                |   Originating Router's IP Addr    |
                +-----------------------------------+

   The RD is encoded as described in [RFC4364].

   Usage of intra-AS I-PMSI auto-discovery routes is described in
   Section "MVPN Auto-Discovery/Binding - Intra-AS Operations".


4.2. Inter-AS I-PMSI auto-discovery route

   An inter-AS I-PMSI auto-discovery route type specific MCAST-VPN NLRI
   consists of the following:

                +-----------------------------------+
                |      RD   (8 octets)              |
                +-----------------------------------+
                |      Source AS (4 octets)         |
                +-----------------------------------+

   The RD is encoded as described in [RFC4364].

   The Source AS contains an Autonomous System number.  Two octets AS
   numbers are encoded in the low order two octets of the Source AS
   field.

   Usage of inter-AS I-PMSI auto-discovery routes is described in
   Section "MVPN Auto-Discovery/Binding - Inter-AS Operations".


4.3. S-PMSI auto-discovery route

   An S-PMSI auto-discovery route type specific MCAST-VPN NLRI consists
   of the following:

                +-----------------------------------+
                |      RD   (8 octets)              |
                +-----------------------------------+
                | Multicast Source Length (1 octet) |
                +-----------------------------------+



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                |  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.  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 Group Address field contains the C-G address.  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.

   Usage of S-PMSI auto-discovery routes is described in Section
   "Switching to S-PMSI".


4.4. Leaf auto-discovery route

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

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

   Usage of Leaf auto-discovery routes is described in Section "MVPN
   Auto-Discovery/Binding - Inter-AS Operations".











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4.5. Source Active auto-discovery route (SA auto-discovery route)

   A Source Active (SA) auto-discovery route type specific MCAST-VPN
   NLRI consists of the following:

                +-----------------------------------+
                |      RD   (8 octets)              |
                +-----------------------------------+
                | Multicast Source Length (1 octet) |
                +-----------------------------------+
                |   Multicast Source (Variable)     |
                +-----------------------------------+
                |  Multicast Group Length (1 octet) |
                +-----------------------------------+
                |  Multicast Group   (Variable)     |
                +-----------------------------------+

   The RD is encoded as described in [RFC4364].

   The Multicast Source field contains the C-S address.  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 Group Address field contains the C-G address.  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.

   Usage of Source Active auto-discovery routes is described in Sections
   "Choosing a single forwarder PE when switching from RPT to SPT", and
   "Co-locating C-RPs on a PE".


4.6. C-Multicast Route

   A Shared Tree Join route, a Source Tree Join route, and a Prune
   Source from Shared Tree route type specific MCAST-VPN NLRI have the
   following encoding:

                +-----------------------------------+
                |      RD   (8 octets)              |
                +-----------------------------------+
                |    Source AS (4 octets)           |
                +-----------------------------------+
                | Multicast Source Length (1 octet) |



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                +-----------------------------------+
                |   Multicast Source (Variable)     |
                +-----------------------------------+
                |  Multicast Group Length (1 octet) |
                +-----------------------------------+
                |  Multicast Group   (Variable)     |
                +-----------------------------------+

   The RD is encoded as described in [RFC4364].

   The Source AS contains an Autonomous System number.  Two octets AS
   numbers are encoded in the low order two octets of the Source AS
   field.

   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 Multicast Source field contains the C-S address.

   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.

   Usage of C-multicast routes is described in Section "VPN C-Multicast
   Routing Information Exchange among PEs".

   The Group Address field contains the C-G address.


5. P-Multicast Service Interface Tunnel (PMSI Tunnel) attribute

   This document defines and uses a new BGP attribute, called P-
   Multicast Service Interface Tunnel (PMSI Tunnel) attribute. This is
   an optional transitive BGP attribute. The format of this attribute is
   defined as follows:

                +---------------------------------+
                |  Tunnel Type (2 octets)         |
                +---------------------------------+
                |  MPLS Label (3 octets)          |
                +---------------------------------+
                |  Tunnel Identifier (variable)   |
                +---------------------------------+

   The Tunnel Type identifies the type of the tunneling technology used



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   to establish the PMSI tunnel. The type determines the syntax and
   semantics of the Tunnel Identifier field. This document defines the
   following Tunnel Types:

     + 1 - Leaf Information Required
     + 2 - RSVP-TE P2MP LSP
     + 3 - LDP P2MP LSP
     + 4 - PIM-SSM Tree
     + 5 - PIM-SM Tree
     + 6 - PIM-Bidir Tree
     + 7 - Ingress Replication
     + 8 - LDP MP2MP LSP

   If the MPLS Label field is non-zero, then it contains an MPLS label
   encoded as 3 octets, where the high-order 20 bits contain the label
   value. Absence of MPLS Label is indicated by setting the MPLS Label
   field to zero.

   When the type is set to Leaf Information Required, the Tunnel
   Identifier field is empty (zero length), and the MPLS Label field is
   zero.

   When the type is set to RSVP-TE P2MP LSP, the Tunnel Identifier
   contains the RSVP-TE P2MP LSP's SESSION Object.

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

   When the type is set to PIM-SM Tree, the Tunnel Identifier MUST
   include <Sender Address, P-Multicast Group>, and MAY include P-RP
   Node Address. The node that originated the attribute MUST use the
   address carried in the Sender Address as the source IP address for
   the IP/GRE encapsulation of the MVPN data.

   When the type is set to PIM-SSM Tree, the Tunnel Identifier is <P-
   Root Node Address, P-Multicast Group>. The node that originates the
   attribute MUST use the address carried in the P-Root Node Address as
   the source IP address for the IP/GRE encapsulation of the MVPN data.

   When the type is set to PIM-Bidir Tree, the Tunnel Identifier is
   <Sender Address, P-Multicast Group>. The node that originated the
   attribute MUST use the address carried in the Sender Address as the
   source IP address for the IP/GRE encapsulation of the MVPN data.

   When the type is set to Ingress Replication the Tunnel Identifier
   carries the unicast tunnel endpoint.

   When the type is set to LDP MP2MP LSP, the Tunnel Identifier is <P-



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   Root Node Address, Variable length opaque identifier>.

   If LDP MP2MP LSPs are used as PMSI tunnels, the router that
   transmitted a given packet into the tunnel cannot be identified.  As
   a result, LDP MP2MP LSPs do not support aggregation, and therefore
   can only be used as unaggregated tunnels. Support of aggregation with
   LDP MP2MP LSPs is a matter for further study. In addition, if an LDP
   MP2MP LSP is used within a given AS as an intra-AS segment of an
   inter-AS tunnel, a single ASBR within that AS must be chosen to be
   the one which transmits packets to and from the upstream segment of
   the inter-AS tunnel. In the absence of the procedures for doing this,
   LDP MP2MP LSPs can not be used for intra-AS segments of inter-AS
   tunnels. Procedures for choosing a single ASBR are a matter for
   further study. Finally, use of LDP MP2MP LSPs makes choosing a single
   forwarder PE (see section "Choosing a single forwarder PE")
   mandatory.

   The PMSI Tunnel attribute is only used in conjunction with intra-AS
   and inter-AS I-PMSI auto-discovery routes, with S-PMSI auto-discovery
   routes, and with leaf auto-discovery routes.


6. Source AS Extended Community

   This document defines a new extended community called Source AS.

   The Source AS is an AS specific extended community.

   The Source AS extended community is of an extended type, and is
   transitive across AS boundaries.

   To support MVPN a PE that originates a (unicast) route to VPN-IPv4
   addresses MUST include in the BGP Update message that carries this
   route the Source AS extended community, except if it is known a
   priori that none of these addresses will act as multicast sources
   and/or RP, in which case the (unicast) route need not carry the
   Source AS extended community.  The Global Administrator field of this
   community MUST be set to the autonomous system number of the PE. The
   Local Administrator field of this community SHOULD be set to 0.

   Usage of the Source AS extended community is described in Sections
   "PIM as the C-Multicast protocol", "mLDP as the C-Multicast
   protocol", and "Receiving Source Active auto-discovery route".








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7. Route Import Extended Community

   This document defines a new extended community called Route Import.

   The Route Import is an IPv4 address specific extended community.

   The Route Import is of an extended type, and is transitive across AS
   boundaries.

   To support MVPN in addition to the import/export Route Target(s) used
   by the unicast routing, each VRF on a PE MUST have an import Route
   Target that is unique to this VRF, except if it is known a priori
   that none of the (local) MVPN sites associated with the VRF contain
   multicast source(s) and/or RP, in which case the VRF need not have
   this import Route Target. This Route Target MUST be IP address
   specific, and is constructed as follows:

     + The Global Administrator field of the Route Target MUST be set to
       an IP address of the PE. This address MUST be a routable IP
       address.  This address MAY be common for all the VRFs on the PE
       (e.,g., this address may be PE's loopback address).

     + The Local Administrator field of the Route Target associated with
       a given VRF contains a 2 octets long number that uniquely
       identifies that VRF within the PE that contains the VRF
       (procedures for assigning such numbers are purely local to the
       PE, and outside the scope of this document).

   A PE that originates a (unicast) route to VPN-IPv4 addresses MUST
   include in the BGP Updates message that carries this route the Route
   Import extended community that has the value of this Route Target,
   except if it is known a priori that none of these addresses will act
   as multicast sources and/or RP, in which case the (unicast) route
   need not carry the Route Import extended community.

   If a PE uses Route Target Constrain [RT-CONSTRAIN], the PE SHOULD
   advertise all such import Route Targets using Route Target Constrains
   (note that doing this requires just a single Route Target Constraint
   advertisement by the PE). This allows each C-multicast route to reach
   only the relevant PE. 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]).

   Usage of Route Import extended community is described in Sections
   "PIM as the C-Multicast protocol", "mLDP as the C-Multicast
   protocol", and "Receiving Source Active auto-discovery route".





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8. MVPN Auto-Discovery/Binding

   This section specifies procedures for the auto-discovery of MVPN
   memberships and the distribution of information used to instantiate
   I-PMSIs.

   MVPN auto-discovery/binding consists of two components: intra-AS and
   inter-AS. The former provides MVPN auto-discovery/binding within a
   single AS. The latter provides MVPN auto-discovery/binding across
   multiple ASes.

   Note that the inter-AS component applies only to the ASes that use
   either option (b) or (c) for unicast inter-AS operations, as
   specified in Section "Multi-AS Backbones" of [BGP-VPN]. ASes that use
   option (a) need only the intra-AS component.


8.1. MVPN Auto-Discovery/Binding - Intra-AS Operations

   This section describes exchanges of auto-discovery routes
   originated/received by PEs within the same AS.


8.1.1. Originating (intra-AS) auto-discovery routes

   To participate in the MVPN auto-discovery/binding a PE router that
   has a given VRF of a given MVPN MUST originate an auto-discovery
   route and advertises this route in IBGP. The route is constructed as
   follows.

   The route carries a single MCAST-VPN NLRI with the RD set to the RD
   of the VRF, and the Originating Router's IP Address field set to the
   IP address that the PE places in the Global Administrator field of
   the Route Import extended community of the VPN-IPv4 routes advertised
   by the PE. Note that the <RD, Originating Router's IP address> tuple
   uniquely identifies a given multicast VRF.

   Depending on the type of a P-Multicast tree used to instantiate the
   provider tunnel for the MVPN on the PE, the PMSI Tunnel attribute of
   the intra-AS auto-discovery route is constructed as follows.

     + If a P-Multicast tree is used to instantiate the provider tunnel
       for the MVPN on the PE, and either (a) this tree exists at the
       time of discovery, or (b) the PE doesn't need to know the leaves
       of the tree beforehand in order to advertise the P-Multicast tree
       identifier, then the advertising PE SHOULD advertise the type and
       the identity of the P-Multicast tree in the PMSI Tunnel attribute
       of the route.



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     + If a P-Multicast tree is used to instantiate the provider tunnel
       for the MVPN on the PE, and in order to advertise the P-Multicast
       tree identifier the advertising PE needs to know the leaves of
       the tree beforehand, the PE first discovers the leaves by
       advertising an auto-discovery route without the PMSI Tunnel
       attribute. Once the PE obtains the information about the leaves
       (this information is obtained from the auto-discovery routes
       received by the PE), the PE then advertises the binding of the
       tree to the MVPN using the same route as the one used for the
       auto-discovery, with the addition of carrying in the route the
       PMSI Tunnel attribute that contains the type and the identity of
       the P-Multicast tree. In other words, in the first phase the PE
       advertises an auto-discovery route, but with no binding, and
       receives auto-discovery routes from other PEs.  Once this is
       done, in the second phase the PE advertises binding based on the
       information acquired in the first phase. If at some later point a
       new PE advertises participation in the same MVPN, the initial
       binding PMSI Tunnel binding information SHOULD NOT change (though
       the leaves of the corresponding P-Multicast tree may change).

     + When the MVPN is aggregated with other MVPNs onto the same P-
       Multicast tree, advertised in the PMSI Tunnel attribute, the PMSI
       Tunnel attribute MUST carry a MPLS upstream assigned label [MPLS-
       UPSTREAM] that is associated with the MVPN.

     + If the PE that originates the advertisement uses ingress
       replication to instantiate the provider tunnel for the MVPN, the
       route MUST include the PMSI Tunnel attribute with the Tunnel Type
       set to Ingress Replication and Tunnel Identifier set to a
       routable address of the PE. The PMSI Tunnel attribute MUST carry
       a downstream assigned MPLS label. This label is used to
       demultiplex the MVPN traffic received over a unicast tunnel by
       the PE.

     + 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 an MVPN are expected to advertise tunnel
       bindings whose tunnel types are supported by all other PEs that
       are participating in this MVPN and are part of the same AS.

   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 distribution of the auto-discovery routes is
   controlled by the same Route Targets as the ones used for the
   distribution of VPN-IPv4 unicast routes. That is, by default the
   auto-discovery route MUST carry the export Route Target used by the



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   unicast routing.  If any other PE has one of these Route Targets
   configured for a VRF, it treats the advertising PE as a member in the
   MVPN to which the VRF belongs. The default could be modified via
   configuration by having a set of Route Targets used for the auto-
   discovery routes being distinct from the ones used for the VPN-IPv4
   unicast routes (see also section "Non-congruent Unicast and Multicast
   Connectivity").

   To constrain distribution of the intra-AS membership/binding
   information to the AS of the advertising PE the BGP Update message
   originated by the advertising PE SHOULD carry the NO_EXPORT Community
   ([RFC1997]).


8.1.2. Receiving (intra-AS) auto-discovery routes

   When a PE receives a BGP Update message that carries an auto-
   discovery route such that (a) the route was originated by some other
   PE within the same AS as the local PE, (b) at least one of the Route
   Targets of the route matches one of the import Route Targets
   configured for a particular VRF 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 Tunnel Type in the PMSI Tunnel attribute is set to Ingress
   Replication, then the MPLS label and the address carried in the
   Tunnel Identifier field of the PMSI Tunnel attribute should be used
   when the local PE sends multicast traffic to the PE that originated
   the route.

   If the Tunnel Type in the PMSI Tunnel attribute is set to LDP P2MP
   LSP, or PIM-SSM tree, or PIM-SM tree, or PIM-Bidir tree, the PE
   SHOULD join the P-Multicast tree whose identity is carried in the
   Tunnel Identifier.

   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, or MAY be established after 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 VRF that has at least one
   of its import Route Targets that matches one of the Route Targets of



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   the received auto-discovery route.

   If the PMSI Tunnel attribute has the Tunnel Type set to LDP P2MP LSP,
   or PIM-SSM tree, or PIM-SM tree, or PIM-Bidir tree, or RSVP-TE P2MP
   LSP, and the attribute also carries an MPLS label, then this is 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 assigned label are forwarded using the VRF that has at least
   one of its import Route Target that matches one of the Route Targets
   of the received auto-discovery route.


8.2. MVPN Auto-Discovery/Binding - Inter-AS Operations

   An Autonomous System Border Router (ASBR) may be configured to
   support a particular MVPN as follows:

     + An ASBR MUST be be configured with a set of (import) Route
       Targets (RTs) that specifies the set of MVPNs supported by the
       ASBR. These Route Targets control acceptance of intra-AS/inter-AS
       auto-discovery routes by the ASBR. As long as unicast and
       multicast connectivity are congruent, this could be the same set
       of Route Targets as the one used for supporting unicast (and
       therefore would not require any additional configuration above
       and beyond of what is required for unicast).

     + The ASBR MUST be configured with an import Route Target that 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 inter-AS auto-discovery routes and S-PMSI auto-discovery
       routes advertised by this ASBR (if the ASBR uses different Next
       Hops, then the ASBR MUST be 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 ASBR supports Route
       Target Constrain [RT-CONSTRAIN], the ASBR SHOULD advertise this
       import Route Target within its own AS using Route Target
       Constrains. Note that this Route Target controls acceptance of
       leaf auto-discovery routes and C-multicast routes by the ASBR,
       and is used to constrain distribution of both leaf auto-discovery
       routes and C-multicast routes (see Section "VPN C-Multicast
       Routing Information Exchange among PEs").  To constrain
       distribution of the Route Target Constrain routes to the AS of
       the advertising ASBR these routes SHOULD carry the NO_EXPORT
       Community ([RFC1997]).







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     + The ASBR MUST be configured with the tunnel types for the intra-
       AS segments of the MVPNs supported by the ASBR, as well as
       (depending on the tunnel type) the information needed to create
       the PMSI attribute for these tunnel types.

     + If the ASBR originates an inter-AS auto-discovery route for a
       particular MVPN present on some of the PEs within its own AS, the
       ASBR MUST be configured with an RD for that MVPN. To allow
       aggregation of inter-AS auto-discovery routes it is RECOMMENDED
       that all the ASBRs within an AS that are configured to originate
       an inter-AS auto-discovery route for a particular MVPN be
       configured with the same RD (although for a given MVPN each AS
       may assign this RD on its own, without coordination with other
       ASes).

   If an ASBR is configured to support a particular MVPN, the ASBR MUST
   participate in the intra-AS MVPN auto-discovery/binding procedures
   for that MVPN within the ASBR's own AS, as defined in this document.

   Moreover, in addition to the above the ASBR performs the following
   procedures.


8.2.1. Originating Inter-AS MVPN Auto-Discovery routes

   For a given MVPN configured on an ASBR when the ASBR determines
   (using the intra-AS auto-discovery procedures) that at least one of
   the PEs of its own AS has (directly) connected site(s) of the MVPN,
   the ASBR originates an inter-AS auto-discovery route and advertises
   it in EBGP. The route is constructed as follows:

     + The route carries a single MCAST-VPN NLRI with the RD set to the
       RD configured for that MVPN on the ASBR, and the Source AS set to
       the Autonomous System number of the ASBR.

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

     + By default the route MUST carry the export Route Target used by
       the unicast routing of that VPN. The default could be modified
       via configuration by having a set of Route Targets used for the
       inter-AS auto-discovery routes being distinct from the ones used
       by the unicast routing of that VPN (see also section "Non-
       congruent Unicast and Multicast Connectivity").

   An inter-AS auto-discovery route for a given <AS, MVPN> indicates
   presence of the MVPN sites connected to one or more PEs of the AS.




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   An inter-AS auto-discovery route originated by an ASBR aggregates
   (intra-AS) auto-discovery routes originated within the ASBR's own AS.
   Thus while the auto-discovery routes originated within an AS are at
   the granularity of <PE, MVPN> within that AS, outside of that AS the
   (aggregated) inter-AS auto-discovery routes could be at the
   granularity of <AS, MVPN>.


8.2.2. Propagating Inter-AS MVPN Auto-Discovery routes

   An inter-AS auto-discovery route for a given MVPN, 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 installs an inter-AS auto-discovery route for
   MVPN V that originated at a particular AS, AS1. The BGP next hop of
   that route becomes A's "upstream neighbor" on a multicast
   distribution tree for V that is rooted at AS1. When the inter-AS
   auto-discovery routes have been distributed to all the necessary
   ASes, they define a "reverse path" from any AS that supports MVPN V
   back to AS1. For instance, if AS2 supports MVPN V, then there will be
   a reverse path for MVPN V from AS2 to AS1. This path is a sequence of
   ASBRs, the first of which is in AS2, and the last of which is in AS1.
   Each ASBR in the sequence is the BGP next hop of the previous ASBR in
   the sequence on the given inter-AS auto-discovery route.

   This reverse path information can be used to construct a
   unidirectional multicast distribution tree for MVPN V, containing all
   the ASes that support V, and having AS1 at the root. We call such a
   tree an "inter-AS tree". Multicast data originating in MVPN sites
   connected to PEs within a given AS will travel downstream along the
   tree which is rooted at that AS.

   The path along an inter-AS tree is a sequence of ASBRs; it is still
   necessary to specify how the multicast data gets from a given ASBR to
   the set of ASBRs which are immediately downstream of the given ASBR
   along the tree. This is done by creating "segments": ASBRs in
   adjacent ASes will be connected by inter-AS segments, ASBRs in the
   same AS will be connected by "intra-AS segments".

   An ASBR initiates creation of an intra-AS segment when the ASBR
   receives an inter-AS auto-discovery route from an EBGP neighbor.
   Creation of the segment is completed as a result of distributing via
   IBGP this route within the ASBR's own AS.

   For a given inter-AS tunnel each of its intra-AS segments could be
   constructed by its own independent mechanism. Moreover, by using



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   upstream assigned labels within a given AS multiple intra-AS segments
   of different inter-AS tunnels of either the same or different MVPNs
   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, any PIM variant), 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. 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 it is also necessary to use "leaf auto-
   discovery" routes. The precise conditions under which leaf auto-
   discover routes need to be used are described in subsequent sections.

   Since (aggregated) inter-AS auto-discovery routes could have
   granularity of <AS, MVPN>, an MVPN that is present in N ASes could
   have total of N inter-AS tunnels. Thus for a given MVPN the number of
   inter-AS tunnels is independent of the number of PEs that have this
   MVPN.

   The following sections specify procedures for propagation of
   (aggregated) inter-AS auto-discovery routes across ASes.


8.2.2.1. Inter-AS Auto-Discovery Route received via EBGP

   When an ASBR receives from one of its EBGP 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 auto-discovery route to other PEs and ASBRs within its own AS.

   When re-advertising an inter-AS auto-discovery route the ASBR MUST
   set the Next Hop field of the MP_REACH_NLRI attribute to a routable
   IP address of the ASBR.

   Depending on the type of a P-Multicast tree used to instantiate the
   intra-AS segment of the inter-AS tunnel, the PMSI Tunnel attribute of
   the re-advertised inter-AS auto-discovery route is constructed as
   follows:





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     + If the ASBR uses ingress replication to instantiate the intra-AS
       segment of the inter-AS tunnel, the re-advertised route SHOULD
       carry the PMSI Tunnel attribute with the Tunnel Type set to
       Ingress Replication, but no MPLS labels.

     + If the ASBR uses a P-Multicast tree to instantiate the intra-AS
       segment of the inter-AS tunnel, and in order to advertise the P-
       Multicast tree identifier the ASBR does not need to know the
       leaves of the tree beforehand, then the advertising ASBR SHOULD
       advertise the type and the identity of the P-Multicast tree in
       the PMSI Tunnel attribute of the route. This, in effect, creates
       a binding between the inter-AS auto-discovery route and the P-
       Multicast tree.

     + If the ASBR uses a P-Multicast tree to instantiate the intra-AS
       segment of the inter-AS tunnel, and in order to advertise the P-
       Multicast tree identifier the advertising ASBR needs to know the
       leaves of the tree beforehand, the inter-AS auto-discovery route
       re-advertised by the ASBR MUST include the PMSI Tunnel attribute
       with the Tunnel Type set to Leaf Information Required. As a
       result the ASBR first discovers the leaves using the procedures
       specified in "Leaf Auto-Discovery route received via IBGP". The
       ASBR then advertises the binding of the tree to the inter-AS
       auto-discovery route using the original inter-AS auto-discovery
       route, with the addition of carrying in the route the PMSI Tunnel
       attribute that contains the type and the identity of the tree. In
       other words, in the first phase the ASBR advertises inter-AS
       auto-discovery routes, but with no binding. Once this is done, in
       the second phase the ASBR advertises binding based on the
       information acquired in the first phase.

     + When multiple inter-AS auto-discovery routes are bound onto the
       same P-Multicast tree advertised in the PMSI Tunnel attribute,
       the PMSI Tunnel attribute MUST carry a MPLS upstream assigned
       label [MPLS-UPSTREAM] that is associated with the inter-AS auto-
       discovery route.

   In addition the ASBR MUST send to the EBGP neighbor, from whom it
   receives the inter-AS auto-discovery route, a BGP Update message that
   carries a leaf auto-discovery route constructed as follows.

     + The route carries a single MCAST-VPN NLRI with the Route Key
       field set to the MCAST-VPN NLRI of the inter-AS auto-discovery
       route received from that neighbor and the Originating Router's IP
       address set to the IP address of the ASBR (this MUST be a
       routable IP address).





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     + 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
       MVPN traffic received over a unicast tunnel by the advertising
       router.

     + The ASBR constructs an IP-based Route Target community by placing
       the IP address carried in the next hop of the received inter-AS
       auto-discovery route in the Global Administrator field of the
       community, with the Local Administrator field of this community
       set to 0, and sets the Extended Community attribute of the leaf
       auto-discovery route to that community.

     + The Next Hop field of the MP_REACH_NLRI attribute of the route
       SHOULD be set to the same IP address as the one carried in the
       Originating Router's IP Address field of the route.

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


8.2.2.2. Leaf Auto-Discovery Route received via EBGP

   When an ASBR receives via EBGP a leaf auto-discovery route, the ASBR
   accepts the route only if the Route Target carried in the Extended
   Community attribute of the route matches one of the import Route
   Target configured on the ASBR.

   If the ASBR accepts the leaf auto-discovery route, the ASBR finds an
   inter-AS auto-discovery route whose MCAST-VPN NLRI has the same value
   as the Route Key field of the 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 inter-AS
   auto-discovery route.


8.2.2.3. Inter-AS Auto-Discovery Route received via IBGP

   In the context of this section we use the term "PE/ASBR router" to
   denote either a PE or an ASBR router.

   If a given inter-AS auto-discovery route is advertised within an AS
   by multiple ASBRs of that AS, the BGP best route selection performed
   by other PE/ASBR routers within the AS does not require all these



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   PE/ASBR routers to select the route advertised by the same ASBR - to
   the contrary different PE/ASBR routers may select routes advertised
   by different ASBRs.

   When a PE/ASBR router receives from one of its IBGP neighbors a BGP
   Update message that carries an inter-AS auto-discovery route, if (a)
   at least one of the Route Targets carried in the message matches one
   of the import Route Targets configured on the PE/ASBR, and (b) the
   PE/ASBR determines that the received route is the best route to the
   destination carried in the NLRI of the route, the PE/ASBR performs
   the following operations.

   If the router is an ASBR then the ASBR propagates the route to its
   EBGP neighbors. When propagating the route to the EBGP neighbors the
   ASBR MUST set the Next Hop field of the MP_REACH_NLRI attribute to a
   routable IP address of the ASBR.

   If the received inter-AS auto-discovery route carries the PMSI Tunnel
   attribute with the Tunnel Type set to LDP P2MP LSP, or PIM-SSM tree,
   or PIM-SM tree, or PIM-Bidir tree, the PE/ASBR SHOULD join the P-
   Multicast tree whose identity is carried in the Tunnel Identifier.

   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, or PIM-SSM, or PIM-SM tree, or PIM-Bidir tree, 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 MVPN advertised by the inter-AS auto-
   discovery route and rooted at the AS that originated the inter-AS
   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 MVPN, packets received over the intra-AS segment
   must be forwarded to the local receivers using the local VRF.

   If the Tunnel Type in the PMSI Tunnel attribute of the received
   inter-AS auto-discovery route is set to either Leaf Information
   Required or Ingress Replication, then the PE/ASBR originates a new
   leaf auto-discovery route as follows.



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     + The route carries a single MCAST-VPN NLRI with the Route Key
       field set to the MCAST-VPN NLRI of the inter-AS auto-discovery
       route received from that neighbor, and the Originating Router's
       IP address set to the IP address of the ASBR (this MUST be a
       routable IP address).

     + If the received inter-AS auto-discovery route carries the PMSI
       Tunnel attribute with the Tunnel Type set to Ingress Replication,
       then the leaf auto-discovery route MUST carry the PMSI Tunnel
       attribute with the Tunnel Type set to Ingress Replication. The
       Tunnel Identifier MUST carry a routable address of the PE/ASBR.
       The PMSI Tunnel attribute MUST carry a downstream assigned MPLS
       label that is used to demultiplex the MVPN traffic received over
       a unicast tunnel by the PE/ASBR.

     + The PE/ASBR constructs an IP-based Route Target community by
       placing the IP address carried in the next hop of the received
       inter-AS auto-discovery route in the Global Administrator field
       of the community, with the Local Administrator field of this
       community set to 0, and sets the Extended Community attribute of
       the leaf auto-discovery route to that community.

     + The Next Hop field of the MP_REACH_NLRI attribute of the route
       SHOULD be set to the same IP address as the one carried in the
       Originating Router's IP Address field of the route.

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

     + Once the leaf auto-discovery route is constructed, the PE/ASBR
       advertises this route into IBGP.


8.2.2.4. Leaf Auto-Discovery route received via IBGP

   When an ASBR receives via IBGP a leaf auto-discovery route, the ASBR
   accepts the route only if the Route Target carried in the Extended
   Community attribute of the route matches one of the import Route
   Target configured on the ASBR.

   If the ASBR accepts the leaf auto-discovery route, the ASBR finds an
   inter-AS auto-discovery route whose MCAST-VPN NLRI has the same value
   as the Route Key field of the the leaf auto-discovery route.

   The received route may carry either (a) no PMSI Tunnel attribute, or
   (b) the PMSI Tunnel attribute, but only with the Tunnel Type set to
   Ingress Replication.




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   If the received route does not carry the PMSI Tunnel attribute, the
   ASBR uses the information from the received route to determine the
   leaves of the P-Multicast tree rooted at the ASBR that would be used
   for the intra-AS segment associated with the found inter-AS auto-
   discovery route. The IP address of a leaf is the IP address carried
   in the Originating Router's IP address field of the received leaf
   auto-discovery route.

   If the received route carries the PMSI Tunnel attribute with the
   Tunnel Type set to Ingress Replication the ASBR uses the information
   carried by the route to construct the intra-AS segment with ingress
   replication.


9. Non-congruent Unicast and Multicast Connectivity

   If the multicast connectivity of a MVPN is congruent to its unicast
   connectivity, the VRF of that MVPN, as referred to by this document,
   means the VRF of that VPN used for unicast routing.

   If the multicast connectivity of a MVPN is non-congruent to its
   unicast connectivity, the VRF of that MVPN, as referred to by this
   document, means the VRF that is distinct from the VRF of that VPN
   used for unicast routing. On a given PE such a VRF may have its own
   import and export Route Targets, different from the ones used by the
   VRF used for unicast routing. These Route Targets are used for the
   auto-discovery routes. The export Route Targets are added to the
   Route Targets used for unicast routing when originating VPN-IPv4
   routes. The export Route Targets control the set of sites that could
   receive multicast traffic originated by the sources within the local
   site. The import Route Targets associated with a given VRF are used
   to determine which of the received VPN-IPv4 routes should be accepted
   into the VRF. The import Route Targets control the set of sites that
   contain sources of multicast traffic that could be received within
   the local site.

   If an MVPN site is single-homed to a PE, then on this PE the VRF
   associated with the site should use the same RD as the one used by
   the VRF used for unicast routing of that VPN. If an MVPN site is
   multi-homed to several PEs, then to support non-congruent unicast and
   multicast connectivity on each of these PEs the VRF of the MVPN
   should use its own distinct RD (although on a given PE the RD used by
   the VRF of the MVPN should be the same as the one used by the VRF
   used for unicast routing of that VPN).

   If for a given MVPN all of its sites connected to a given PE are
   known a priori to have no multicast sources, then this PE is NOT
   REQUIRED to originate an auto-discovery route for that MVPN at all,



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   unless either (a) some other PEs that have VRFs in that MVPN use RSVP
   TE P2MP LSPs, in which case the PE originates an auto-discovery
   route, but with no PMSI Tunnel attribute, or (b) the PE uses ingress
   replication for incoming multicast traffic, in which case the PE
   originates an auto-discovery route with the PMSI Tunnel attribute
   indicating ingress replication.


10. VPN C-Multicast Routing Information Exchange among PEs

   VPN C-Multicast Routing Information is exchanged among PEs by using
   C-multicast routes that are carried using MCAST-VPN NLRI. These
   routes are originated and propagated as follows.


10.1. Originating C-Multicast Routes by a PE

10.1.1. Constructing MCAST-VPN NLRI

   Procedures for constructing MCAST-VPN NLRI depend on the multicast
   routing protocol between CE and PE (C-multicast protocol).


10.1.1.1. PIM as the C-Multicast protocol

   The following specifies construction of MCAST-VPN NLRI of C-multicast
   routes for the case where the C-multicast protocol is PIM.  These C-
   multicast routes are originated as a result of updates in <C-S, C-G>
   or <C-*, C-G> or <C-S, C-G, RPT-bit> or <C-*, C-*> state learnt by a
   PE via the C-multicast protocol.

   Whenever a PE creates a new <C-S,C-G> state in one of its MVPN-TIBs,
   if C-S is reachable through some other PE the local PE originates a
   C-multicast route. The Multicast Source field in the MCAST-VPN NLRI
   of the route is set to C-S, the Multicast Group field is set of C-G.
   The MCAST-VPN NLRI is carried as a Source Tree Join route type. The
   semantics of the route is that the PE has one or more receivers for
   <C-S, C-G> in the sites connected to the PE (the route has the <C-S,
   C-G> Join semantics). Whenever a PE deletes a previously created <C-
   S, C-G> state that had resulted in originating a C-multicast route,
   the PE withdraws the route (the withdrawn route has the <C-S, C-G>
   Prune semantics). The MCAST-VPN NLRI of the withdrawn route is
   carried in the MP_UNREACH_NLRI attribute.

   Whenever a PE creates a new <C-*, C-G> state in one of its MVPN-TIBs,
   if the C-RP for C-G is reachable through some other PE the local PE
   originates a C-multicast route. The Multicast Source field in the
   MCAST-VPN NLRI of the route is set to the C-RP address. The Multicast



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   Group field in the MCAST-VPN NLRI is set to the C-G address. The
   MCAST-VPN NLRI of the route is carried as the Shared Tree Join route
   type. The semantics of the route is that the PE has one or more
   receivers for <C-*, C-G> in the sites connected to the PE (the route
   has the <C-*, C-G> Join semantics). Whenever a PE deletes a
   previously created <C-*, C-G> state that had resulted in originating
   a C-multicast route, the PE withdraws the route (the withdrawn route
   has the <C-*, C-G> Prune semantics). The MCAST-VPN NLRI of the
   withdrawn route is carried in the MP_UNREACH_NLRI attribute.

   Whenever a PE creates a new <C-S, C-G, RPT-bit> state in one of its
   MVPN-TIBs, except for the case when this state is created when the PE
   that has an existing <C-*, C-G> state switches from the C-RP based
   tree to the C-S based tree for C-G, if the C-RP is reachable through
   some other PE, the local PE originates a C-multicast route.  The
   Multicast Source field in the MCAST-VPN NLRI of the route is set to
   C-S, and the Multicast Group field is set to C-G. The MCAST-VPN NLRI
   of the route is carried as the Prune Source from Shared Tree route
   type. The semantics of the route is to indicate that the receivers
   for <C-S,C-G> no longer want to receive <C-S, C-G> traffic via the C-
   RP based tree (the route has the <C-S,C-G, RPT> Prune semantics). If
   later on the PE deletes a previously created <C-S, C-G, RPT-bit>
   state, the PE withdraws the route (the semantics of the withdrawn
   route is to indicate that <C-S, C-G> traffic should be carried via
   the C-RP-based tree).  The MCAST-VPN NLRI of the withdrawn route is
   carried in the MP_UNREACH_NLRI attribute.

   Whenever a PE creates a <C-*, C-*> state in one of its MVPN-TIBs, if
   the C-RP is reachable through some other PE the local PE originates a
   C-multicast route. The Multicast Source field in the MCAST-VPN NLRI
   of the route is set to the C-RP address. The Multicast Group field in
   the NLRI MUST be set to a wildcard i.e. 0. The MCAST-VPN NLRI of the
   route is carried as the Shared Tree Join route type.  Whenever a PE
   deletes a previously created <C-*, C-*> state that had resulted in
   originating a C-multicast route, the PE withdraws the route (the
   withdrawn route has the (C-*, C-*) Prune semantics).  The MCAST-VPN
   NLRI of the withdrawn route is carried in the MP_UNREACH_NLRI
   attribute.

   The (local) PE uses its VRF to determine (a) the autonomous system
   number of the (remote) PE that originates the (unicast) route to C-
   S/C-RP, and (b) the import Route Target community associated with the
   VRF on the remote PE which was used to originate the route (this
   information is available from the Route Import extended community
   carried in the unicast VPN-IPv4 routing advertisements by the remote
   PE). Note that for a C-multicast route that the PE originates in
   response to creating a <C-S, C-G, RPT-bit> state, the remote PE is
   the PE that originates the route to C-RP, not to C-S.  The Source AS



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   field in the C-multicast route is set to the found autonomous system.
   The Extended Community attribute of the C-multicast route is set to
   the found Route Target.

   If there is more than one (remote) PE that originates the (unicast)
   route to C-S/C-RP, then the procedures for selecting an upstream PE
   to reach C-S/C-RP are as specified in [MVPN].


10.1.1.2. mLDP as the C-Multicast protocol

   The following specifies construction of MCAST-VPN NLRI of C-multicast
   routes for the case where the C-multicast protocol is mLDP [mLDP].

   Whenever a PE receives from one of its CEs a P2MP Label Map <X, Y, L>
   over interface I, where X is the Root Node Address, Y is the Opaque
   Value, and L is an MPLS label, the PE checks whether it already has
   state for <X, Y> in the VRF associated with the CE. If yes, then all
   the PE needs to do in this case is to update its forwarding state by
   adding <I, L> to the forwarding state associated with <X, Y>.

   If the PE does not have state for <X, Y> in the VRF associated with
   the CE, then the PE constructs a Source Tree Join C-multicast route
   as follows:

     + The PE constructs MCAST-VPN NLRI of the route by placing X into
       the Multicast Source field, and placing Y into the Multicast
       Group field.

     + The PE uses its VRF to determine (a) the autonomous system number
       of the (remote) PE that originates the (unicast) VPN-IPv4 route
       to X, and (b) the import Route Target community associated with
       the VRF on the remote PE which was used to originate the route
       (this information is available from the Route Import extended
       community carried in the unicast VPN-IPv4 routing advertisements
       by the remote PE). The Source AS field in the C-multicast route
       is set to the found autonomous system. The Extended Community
       attribute of the C-multicast route is set to the found Route
       Target.

   Whenever a PE deletes a previously created <X, Y> state that had
   resulted in originating a C-multicast route, the PE withdraws the C-
   multicast route. The MCAST-VPN NLRI of the withdrawn route is carried
   in the MP_UNREACH_NLRI attribute.







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10.1.2. Constructing the rest of the C-multicast route

   The rest of the C-multicast route is constructed as follows (the same
   procedures apply to both PIM and mLDP as the C-Multicast protocol).

   If the local and the remote PEs are in the same AS, then the RD of
   the advertised MCAST-VPN NLRI is set to the RD of the VPN-IPv4 route
   that contains the address carried in the Multicast Source field.  The
   C-multicast route is then advertised into IBGP.

   If the local and the remote PEs are in different ASes, then the local
   PE finds in its VRF an inter-AS auto-discovery route whose Source AS
   field carries the autonomous system number of the remote PE that
   originates the (unicast) route to the address carried in the
   Multicast Source field. The RD of the found inter-AS auto-discovery
   route is used as the RD of the advertised C-multicast route. The
   local PE constructs an IP-based Route Target community by placing the
   next hop of the found inter-AS auto-discovery route in the Global
   Administrator field of this community, with the Local Administrator
   field of this community set to 0, and adds this community to the
   Extended Community attribute of the C-multicast route.

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

   If the next hop of the found inter-AS auto-discovery route is an EBGP
   neighbor of the local PE, then the PE advertises the C-multicast
   route to that neighbor. If the next hop of the found inter-AS auto-
   discovery route is within the same AS as the local PE, then the PE
   advertises the C-multicast route into IBGP.


10.1.3. Unicast Route Changes

   Whenever unicast route used for determining PE connected to C-S/C-RP
   changes, the local PE updates and re-originates the previously
   originated C-multicast routes, as appropriate.


10.2. Propagating C-Multicast routes by an ASBR

   When an ASBR receives a BGP Update message that carries a C-multicast
   route, if at least one of the Route Targets of the route matches one
   of the import Route Targets configured on the ASBR, the ASBR finds an
   inter-AS auto-discovery route whose RD and Source AS matches the RD
   and Source AS carried in the C-multicast route. If no matching route
   is found, the PE discards the received C-multicast route.  Otherwise
   (if a matching route is found) the PE proceeds as follows.



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   When an ASBR receives a BGP Update message that carries a C-multicast
   route, the ASBR first checks if it already has one or more C-
   multicast routes that have the same MCAST-VPN NLRI as the newly
   received route. If such route(s) already exists, the ASBR keeps the
   newly received route, but SHALL not re-advertise the newly received
   route.  Otherwise, the ASBR re-advertises the route, as described
   further down.

   When an ASBR receives a BGP Update message that carries a withdraw of
   a previously advertised C-multicast route, the ASBR first checks if
   it already has at least one C-multicast route that has the same
   MCAST-VPN NLRI. If such a route already exists, the ASBR processes
   the withdrawn route, but SHALL not re-advertise the withdrawn route.
   Otherwise, the ASBR re-advertise the withdraw of a previously
   advertised C-multicast route, as described below.

   If the next hop for the found inter-AS auto-discovery route is an
   EBGP neighbor of the ASBR, then the ASBR re-advertises the C-
   multicast route to that neighbor. If the next hop for the found
   inter-AS auto-discovery route is an IBGP neighbor of the ASBR, the
   ASBR re-advertises the C-multicast route into IBGP. If it is the ASBR
   that originated the found inter-AS auto-discovery route in the first
   place, then the ASBR just re-advertises the C-multicast route into
   IBGP.

   Unless it is the ASBR that originating the found inter-AS auto-
   discovery route in the first place, then before re-advertising the C-
   multicast route, the ASBR modifies the Extended Community attribute
   of the C-multicast route as follows. If the Route Target of the route
   that matches one of the import Route Targets configured on the ASBR
   is an IP-based Route Target with the Global Administrator field set
   to the IP address of ASBR, then the ASBR replaces this Route Target
   with a newly constructed IP-based Route Target that has the Global
   Administrator field set to the Next Hop of the found inter-AS auto-
   discovery route, and Local Administrator field of this community set
   to 0. The rest of the Extended Community attribute of the route
   SHOULD be passed unmodified.

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











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10.3. Receiving C-Multicast Routes by a PE

   When a PE receives a C-multicast route the PE checks if any of the
   Route Target communities carried in the Extended Community attribute
   of the route match any of the import Route Target communities
   associated with the VRFs maintained by the PE. If no match is found
   the PE SHOULD discard the route. Otherwise, (if a match is found),
   the PE checks if the address carried in the Multicast Source field of
   the C-multicast route matches one of the (unicast) VPN-IPv4 routes
   advertised by PE from the VRF. If no match is found the PE SHOULD
   discard the route. Otherwise, (if a match is found), the PE proceeds
   as follows.

   Procedures for a PE to process received C-multicast routes depend on
   the multicast routing protocol between CE and PE (C-multicast
   protocol).


10.3.1. PIM as the C-Multicast protocol

   The following described procedures when PIM is used as the multicast
   routing protocol between CE and PE (C-multicast protocol).


10.3.1.1. Source Tree Join C-Multicast route

   If the received route has the route type set to Source Tree Join,
   then the PE creates a new <C-S, C-G> state in its MVPN-TIB from the
   Multicast Source and Multicast Group fields in the MCAST-VPN NLRI of
   the route, if such a state does not already exist. If there is no S-
   PMSI for <C-S, C-G> then the PE adds an I-PMSI to the outgoing
   interface list of the state if it is not already there. If there is
   an S-PMSI for <C-S, C-G> then the PE add S-PMSI to the outgoing
   interface list of the state if it is not already there.


10.3.1.2. Shared Tree Join C-Multicast route

   If the received route has the route type set to Shared Tree Join,
   then the PE creates a new <C-*, C-G> state in its MVPN-TIB with the
   RP address for that state taken from the Multicast Source, and C-G
   for that state taken from the Multicast Group fields of the MCAST-VPN
   NLRI of the route, if such a state does not already exist. The PE
   adds I-PMSI to the outgoing interface list of the state if it is not
   already there.






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10.3.1.3. Prune Source from Shared Tree C-Multicast route

   If the received route has the route type set to Prune Source from
   Shared Tree, then the PE creates a new <C-S, C-G, RPT-bit> state in
   its MVPN-TIB from the Multicast Source and Multicast Group fields in
   the MCAST-VPN NLRI of the route, if such a state does not already
   exist.


10.3.2. mLDP as the C-Multicast protocol

   The following described procedures when mLDP is used as the multicast
   routing protocol between CE and PE (C-multicast protocol).

   When mLDP is used as a C-multicast protocol, the only valid type of a
   C-multicast route that a PE could receive is a Source Tree Join C-
   multicast route.

   When the PE receives a Source Tree Join C-multicast route, the PE
   creates a new <X, Y> state in its MVPN-TIB from the Multicast Source
   and Multicast Group fields in the MCAST-VPN NLRI of the route, if
   such a state does not already exist. If there is no S-PMSI for <X, Y>
   then the PE creates and advertises an S-PMSI for <X, Y>, as described
   in section "Switching to S-PMSI". If there is an S-PMSI for <X, Y>
   then the PE add S-PMSI to the outgoing interface list of the state if
   it is not already there.


10.4. C-multicast Routes Aggregation

   Note that C-multicast routes are "de facto" aggregated by BGP. The
   MCAST-VPN NLRIs advertised by multiple PEs, for a C-multicast route,
   for a particular MVPN, C-S and C-G, are identical.

   Hence a BGP Route Reflector or ASBR that receives multiple such
   routes with the same NLRI will re-advertise only one of these routes
   to other BGP speakers.

   This implies that C-multicast routes for a given (S,G) of a given
   MVPN originated by PEs that are clients of a given Route Reflector
   are aggregated by the Route Reflector. For instance, if multiple PEs
   that are clients of a Route Reflector, have receivers for a specific
   SSM channel of a MVPN, they will all advertise an identical NLRI for
   the "Source Tree Join" C-multicast route. However only one C-
   multicast route will be advertised by the Route Reflector for this
   specific SSM channel of that MVPN, to other PEs and Route Reflectors
   that are clients of the Route Reflector.




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   This also implies that an ASBR aggregates all the received C-
   multicast routes for a given (S,G) of a given MVPN into a single C-
   multicast route.

   Further a BGP receiver, that receives multiple such routes with the
   same NLRI for the same C-multicast route, will potentially create
   forwarding state based on a single C-multicast route. As per the
   procedures described in the section "Receiving C-Multicast Routes by
   a PE", this forwarding state will be the same as the state that would
   have been created based an other route with same NLRI.


11. Switching to S-PMSI

   [MVPN] describes a BGP based procedures for switching to S-PMSI.  S-
   PMSI auto-discovery routes are used for this purpose.

   Procedures for handling an S-PMSI auto-discovery route outside of the
   autonomous system of the PE that originates the route are the same as
   specified in "Propagating Inter-AS MVPN Auto-Discovery Information",
   except that instead of inter-AS auto-discovery routes the procedures
   apply to S-PMSI auto-discovery routes.

   Procedures for receiving an S-PMSI auto-discovery route by a PE
   within the same autonomous system as the PE that originates the route
   are the same as specified in "Inter-AS Auto-Discovery Route received
   via IBGP", except that instead of inter-AS auto-discovery routes the
   procedures apply to S-PMSI auto-discovery routes.

   The following describes procedures for originating S-PMSI auto-
   discovery routes by a PE.


11.1. Originating S-PMSI auto-discovery routes

   An S-PMSI auto-discovery route instantiated for a given <C-S, C-G>
   multicast stream is constructed as follows.

   The MCAST-VPN NLRI of the route is constructed as follows.

     + The RD in this NLRI is set to the RD of the VRF associated with
       <C-S, C-G>.

     + 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.





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     + 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.

     + The Originating Router's IP Address field MUST be set to the IP
       address that the PE places in the Global Administrator field of
       the Route Import extended community of the VPN-IPv4 routes
       advertised by the PE. Note that the <RD, Originating Router's IP
       address> tuple uniquely identifies a given multicast VRF.

   Depending on the type of a P-Multicast tree used to instantiate the
   S-PMSI, the PMSI Tunnel attribute of the S-PMSI auto-discovery route
   is constructed as follows:

     + If a P-Multicast tree is used to instantiate the S-PMSI, and in
       order to advertise the P-Multicast tree identifier the PE does
       not need to know the leaves of the tree within its own AS
       beforehand, then the advertising PE SHOULD advertise the type and
       the identity of the P-Multicast tree in the PMSI Tunnel attribute
       of the route.  This, in effect, creates a binding between the S-
       PMSI auto-discovery route and the P-Multicast tree.

     + If a P-Multicast tree is used to instantiate the S-PMSI, and in
       order to advertise the P-Multicast tree identifier the
       advertising PE needs to know the leaves of the tree within its
       own AS beforehand, the S-PMSI auto-discovery route advertised by
       the PE MUST include the PMSI Tunnel attribute with the Tunnel
       Type set to Leaf Information Required. As a result the PE first
       discovers the leaves using the procedures specified in "Leaf
       Auto-Discovery route received via IBGP", except that instead of
       inter-AS auto-discovery routes the procedures applied to S-PMSI
       auto-discovery routes. The PE then advertises the binding of the
       P-Multicast tree to the S-PMSI auto-discovery route using the
       original S-PMSI auto-discovery route with the addition of
       carrying in the route the PMSI Tunnel attribute that contains the
       type and the identity of the tree. In other words, in the first
       phase the PE advertises an S-PMSI auto-discovery route, but with
       no binding. Once this is done, in the second phase the PE
       advertises binding based on the information acquired in the first
       phase.

     + When within a given AS multiple S-PMSI auto-discovery routes are
       bound onto the same P-Multicast tree advertised in the PMSI
       Tunnel attribute, the PMSI Tunnel attribute MUST carry an MPLS
       upstream assigned label [MPLS- UPSTREAM] that is associated with
       the individual S-PMSI auto-discovery route.

   The Next Hop field of the MP_REACH_NLRI attribute of the route SHOULD



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   be set to the same IP address as the one carried in the Originating
   Router's IP Address field.

   The route SHOULD carry the same set of Route Targets as the intra-AS
   auto-discovery route of the MVPN originated by the PE


12. Carrier's Carrier

   A way to support the Carrier's Carrier model is provided by using
   mLDP as the CE-PE multicast routing and label distribution protocol.
   Use of RSVP-TE and/or BGP as the CE-PE multicast routing and label
   distribution protocol is for further study.

   To improve scalability it is strongly recommended that for the
   Carrier's Carrier scenario within an AS all the S-PMSIs of a given
   MVPN be aggregated into a single P-Multicast tree (by using upstream
   assigned labels).


13. Choosing a single forwarder PE when switching from RPT to SPT

   In the scenario where an MVPN customer switches from an C-RP based
   tree (RPT) to the shortest path tree (SPT), in order to avoid packet
   duplication choosing of a single consistent upstream PE, as described
   in [MVPN], may not suffice. To illustrate this consider a set of PEs
   {PE2, PE4, PE6} that are on the C-RP tree for <C-*, C-G> and have
   chosen a consistant upstream PE, as described in [MVPN], for <C-*, C-
   G> state. Further this upstream PE, say PE1, is using an MI-PMSI for
   <C-*, C-G>. If a site attached to one of these PEs, say PE2, switches
   to the C-S tree for <C-S, C-G>, PE2 generates a Source Tree Join C-
   multicast route towards the upstream PE that is on the path to C-S,
   say PE3. PE3 also uses the MI-PMSI for <C-S, C-G>, as PE1 uses for
   <C-*, C-G>. This results in {PE2, PE4, PE6} receiving duplicate
   traffic for <C-S, C-G> - both on the C-RP tree (from PE1) and C-S
   tree (from PE3). If it is desirable to suppress receiving duplicate
   traffic then it is necessary to choose a single forwarder PE for <C-
   S, C-G>. The following describes how this is achieved.


13.1. Source Within a Site - Source Active Advertisement

   Whenever a PE creates an <C-S,C-G> state as a result of receiving a
   Source Tree Join C-multicast route for <C-S, C-G> from some other PE,
   the PE that creates the state SHOULD originate a Source Active auto-
   discovery route. The route carries a single MCAST-VPN NLRI
   constructed as follows:




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     + The RD in this NLRI is set to the RD of the VRF of the MVPN on
       the PE.

     + The Multicast Source field MUST be set to C-S. The Multicast
       Source Length field is set appropriately to reflect this.

     + The Multicast Group field MUST be set to C-G. The Multicast Group
       Length field is set appropriately to reflect this.

   The route SHOULD carry the same set of Route Targets as the intra-AS
   auto-discovery route of the MVPN originated by the PE.

   Using the normal BGP procedures the Source Active auto-discovery
   route is propagated to all the PEs of the MVPN.

   Whenever the PE deletes the <C-S, C-G> state that was previousely
   created as a result of receiving a C-multicast route for <C-S, C-G>
   from some other PE, the PE that deletes the state also withdraws the
   Source Active auto-discovery route, if such a route was advertised
   when the state was created.


13.2. Receiving Source Active auto-discovery route

   When a PE receives a new Source Active auto-discovery route that
   carries a given <C-S, C-G>, the PE finds a VRF whose import Route
   Targets match one or more of the Route Targets carried by the route.
   The PE then checks for an <*, C-G> or an <C-S, C-G> entry in that VRF
   with a non-empty outgoing interface list that contains one or more
   PE-CE interfaces (interfaces from the PE to its directly connected
   CEs). Presence of such an entry implies that some system in the sites
   (directly) connected to the PE is interested in the <C-S, C-G>
   carried in the Source Active auto-discovery route, in which case the
   PE originates a Source Tree Join C-multicast route for <C-S, C-G>.

   If a PE receives from one of its directly connected CEs a PIM Join
   message for a new group C-G, the PE SHOULD originate a Source Tree
   Join C-multicast route for each Source Active auto-discovery route
   that contains C-G and is present in the VRF associated with the CE.

   Construction and distribution of the Source Tree Join C-multicast
   route follows the procedures specified in "VPN C-Multicast Routing
   Information Exchange among PEs", except that procedures specified in
   "Constructing MCAST-VPN NLRI" are replaced with the following:







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     + The Multicast Source Length, Multicast Source, Multicast Group
       Length, and Multicast Group fields are copied from the
       corresponding field in the Source Active auto-discovery route.

     + The (local) PE uses its VRF to find (a) the autonomous system
       number of the (remote) PE that originates the (unicast) route to
       C-S carried in the Multicast Source field of the Source Active
       auto-discovery route, and (b) the import Route Target community
       associated with the VRF on the remote PE which was used to
       originate the (unicast) route (this information is available from
       the Route Import extended community carried in the unicast VPN-
       IPv4 routing advertisements by the remote PE). The Source AS
       field in the C-multicast route is set to the found autonomous
       system. The Extended Community attribute of the C-multicast route
       is set to the found Route Target.

       If there is more than one (remote) PE that originates the
       (unicast) route to C-S, then the procedures for selecting an
       upstream PE to reach C-S are as specified in [MVPN].

   If the incoming interface list (iif) for the <*, C-G> state in the
   MVPN-TIB on the PE contains one of the PE-CE interfaces (interfaces
   from the PE to its directly connected CEs), then the PE creates in
   the MVPN-TIB a <C-S, C-G, RPT-bit> state, if it does not already
   exist. C-S of this state is set to the address carried in the
   Multicast Source field of the Source Active auto-discovery route, and
   C-G of this state is set to the address carried in the Multicast
   Group field of the route. Creating this state results in pruning <C-
   S, C-G> traffic off the shared (RPT) tree.


14. Co-locating C-RPs on a PE

   This section describes the procedures for co-locating a C-RP on a PE.
   The procedures are for the anycast RP based on C-(*, G) scheme
   described in [MVPN].


14.1. Source Within a Site - Source Active Advertisement

   When a PE that acts as an anycast RP for a given MVPN first learns of
   a new (multicast) sender within that MVPN, e.g., via PIM register
   messages originated within that MVPN, the PE follows the normal PIM
   procedures.  In addition, the PE constructs a Source Active auto-
   discovery route, and sends this route to all other PEs that have one
   or more sites of that MVPN connected to them. The route carries a
   single MCAST-VPN NLRI constructed as follows:




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     + The RD in this NLRI is set to the RD of the VRF of the MVPN on
       the PE.

     + The Multicast Source field MUST be set to the source IP address
       of the multicast data packet carried in the PIM-Register message.
       The Multicast Source Length field is set appropriately to reflect
       this.

     + The Multicast Group field MUST be set to the group address of the
       multicast data packet carried in the PIM-Register message. The
       Multicast Group Length field is set appropriately to reflect
       this.

   The route SHOULD carry the same set of Route Targets as the intra-AS
   auto-discovery route of the MVPN originated by the PE.

   Using the normal BGP procedures the Source Active auto-discovery
   route is propagated to all the PEs of the MVPN.

   When a PE that previousely advertised a Source Active auto-discovery
   route for a given sender learns that the sender is no longer active
   the PE withdraws the previously advertised Source Active route.


14.2. Receiver(s) Within a Site

   When a PE receives a new Source Active auto-discovery route that
   carries a given <C-S, C-G>, the PE finds a VRF whose import Route
   Targets match one or more of the Route Targets carried by the route.
   The PE then checks for an <*, C-G> or an <C-S, C-G> entry in that VRF
   with a non-empty outgoing interface list that contains one or more
   PE-CE interfaces (interfaces from the PE to its directly connected
   CEs). Presence of such an entry implies that some system in the sites
   (directly) connected to the PE is interested in the <C-S, C-G>
   carried in the Source Active auto-discovery route, in which case the
   PE originates a Source Tree Join C-multicast route for <C-S, C-G>.

   If a PE receives from one of its directly connected CEs a PIM Join
   message for a new group C-G, the PE SHOULD originate a Source Tree
   Join C-multicast route for each Source Active auto-discovery route
   that contains C-G and is present in the VRF associated with the CE.

   Construction and distribution of the Source Tree Join C-multicast
   route follows the procedures specified in "VPN C-Multicast Routing
   Information Exchange among PEs", except that procedures specified in
   "Constructing MCAST-VPN NLRI" are replaced with the following:





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     + The Multicast Source Length, Multicast Source, Multicast Group
       Length, and Multicast Group fields are copied from the
       corresponding field in the Source Active auto-discovery route.

     + The (local) PE uses its VRF to find (a) the autonomous system
       number of the (remote) PE that originates the (unicast) route to
       C-S carried in the Multicast Source field of the Source Active
       auto-discovery route, and (b) the import Route Target community
       associated with the VRF on the remote PE which was used to
       originate the (unicast) route (this information is available from
       the Route Import extended community carried in the unicast VPN-
       IPv4 routing advertisements by the remote PE). The Source AS
       field in the C-multicast route is set to the found autonomous
       system. The Extended Community attribute of the C-multicast route
       is set to the found Route Target.

       If there is more than one (remote) PE that originates the
       (unicast) route to C-S, then the procedures for selecting an
       upstream PE to reach C-S are as specified in [MVPN].

   A PE which receives C-Join for <C-*, C-G> or <C-S, C-G> from one of
   its connected CEs that belong to a given MVPN does not send the
   information that it has receiver(s) for C-G until it receives an
   Source Active auto-discovery route from some other PE indicating that
   there are active sources for that C-G.


14.3. Receiving C-multicast routes

   In this model the only valid type of a C-multicast route that a PE
   could receive is a Source Tree Join C-multicast route. Processing of
   such a route follows the procedures specified in "Source Tree Join C-
   Multicast route".


15. Scalability Considerations

   A PE should use Route Target Constrain [RT-CONSTRAIN] to advertise
   the Route Targets that the PE uses for the Route Imports extended
   community (note that doing this requires just a single Route Target
   Constraint advertisement by the PE). This allows each C-multicast
   route to reach only the relevant PE, rather than all the PEs
   participating the an MVPN.

   To keep the intra-AS membership/binding information within the AS of
   the advertising router the BGP Update message originated by the
   advertising router SHOULD carry the NO_EXPORT Community ([RFC1997]).




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   An inter-AS auto-discovery route originated by an ASBR aggregates
   auto-discovery routes originated within the ASBR's own AS. Thus while
   the auto-discovery routes originated within an AS are at the
   granularity of <PE, MVPN> within that AS, outside of that AS the
   (aggregated) inter-AS auto-discovery routes are at the granularity of
   <AS, MVPN>. An inter-AS auto-discovery route for a given <AS, MVPN>
   indicates the presence of or or more sites of the MVPN connected to
   the PEs of the AS.

   For a given inter-AS tunnel each of its intra-AS segments could be
   constructed by its own 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 MVPNs may
   share the same P-Multicast tree.

   Since (aggregated) inter-AS auto-discovery routes have granularity of
   <AS, MVPN>, an MVPN that is present in N ASes would have total of N
   inter-AS tunnels. Thus for a given MVPN the number of inter-AS
   tunnels is independent of the number of PEs that have this MVPN.

   Within each Autonomous System BGP Route reflectors can be partitioned
   among MVPNs present in that Autonomous System so that each partition
   carries routes for only a subset of the MVPNs supported by the
   Service Provider. Thus no single Route Reflector is required to
   maintain routes for all MVPNs. Moreover, Route Reflectors used for
   MVPN do not have to be used for VPN-IPv4 routes (although they may be
   used for VPN-IPv4 routes as well).

   As described in Section "C-multicast routes aggregation", C-multicast
   routes for a given (S,G) of a given MVPN originated by PEs that are
   clients of a given Route Reflector are aggregated by the Route
   Reflector. Therefore, even if within a Route Reflector cluster there
   are multiple C-multicast routes for a given (S,G) of a given MVPN,
   outside of the cluster all these routes are aggregated into a single
   C-multicast route. Additional aggregation of C-multicast routes
   occurs at ASBRs, where an ASBR aggregates all the received C-
   multicast routes for a given (S,G) of a given MVPN into a single C-
   multicast route. Moreover, both Route Reflectors and ASBRs maintain
   C-multicast routes only in the control plane, but not in the data
   plane.











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16. Dampening of C-multicast routes

   The rate of C-multicast routing changes advertised by a PE is not
   directly proportional to the rate of multicast routing changes within
   the MVPN sites connected to the PE, as after the first <C-S,C-G> Join
   originated within a site, all the subsequent Joins for same <C-S,C-G>
   originated within the sites of the same MVPN connected to the PE do
   not cause origination of new C-multicast routes by the PE.

   Depending on how multicast VPN is engineered, dynamic addition and
   removal of P2MP RSVP-TE leaves through advertisement/withdrawal of
   leaf auto-discovery routes, will happen. Dampening techniques can be
   used to limit corresponding processing.

   To lessen the control plane overhead associated with processing of C-
   multicast routes, this document proposes OPTIONAL route dampening
   procedures similar to what is described in RFC2439. The following
   OPTIONAL procedures can be enabled on a PE, ASBR, or BGP Route
   Reflector advertising or receiving C-multicast routes.


16.1.  Dampening of C-multicast prunes

   A PE/ASBR/Route Reflector can OPTIONALLY delay the advertisement of
   C-multicast prune routes (routes resulting from the removal of
   multicast state). An implementation SHOULD provide the ability to
   control the delay via a configurable timer, possibly with some
   backoff algorithm to adapt the delay to multicast routing activity.

   Dampening of C-multicast prune routes does not impede the multicast
   join latency observed by MVPN customers, and also does not impede the
   multicast leave latency observed by a CE, as multicast forwarding
   from the VRF will stop as soon as C-multicast state is removed in the
   VRF.

   The only potential drawback of dampening C-multicast prune routes is
   that the PE that performs the dampening may receive useless
   (multicast) traffic for some period of time. Note that the PE may
   receive useless (multicast) traffic anyway, irrespective of dampening
   C-multicast prune routes due to the use of I-PMSIs.











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16.2. Dampening of C-multicast joins

   A PE/ASBR/Route Reflector can OPTIONALLY delay the advertisement of
   C-multicast join routes (routes resulting from the creation of
   multicast state). An implementation SHOULD provide the ability to
   control the delay via a configurable timer, possibly with some
   backoff algorithm to adapt the delay to multicast routing activity.

   Dampening C-multicast join routes will not impede multicast join
   latency observed by a given MVPN, except if the PE advertising the C-
   multicast join route is the first for all the sites of the MVPN to do
   so.


16.3. Dampening of leaf auto-discovery routes

   As described in section "Switching to S-PMSI, leaf auto-discovery
   routes are used for S-PMSI tunnel for which the root need to know the
   leaves of the tree.

   Similarly to the procedures proposed above for C-multicast routes,
   dampening can be applied aggressively to the withdrawal of such auto-
   discovery routes.


17. IANA Consideration

   This document defines a new BGP Extended Community called Source AS.
   This community is 2-octet AS specific, of an extended type, and is
   transitive.

   This document defines a new BGP Extended Community called Route
   Import. This community is IPv4 address specific, of an extended type,
   and is transitive.

   This document defines a new NLRI, called MCAST-VPN, to be carried in
   BGP using multiprotocol extensions. It is assigned its own SAFI.

   This document defines a new BGP optional transitive attribute, called
   PMSI Tunnel.











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18. Security Considerations

   The mechanisms described in this document could re-use the existing
   BGP security mechanisms.


19. Acknowledgement

   Some of the text in Section "Co-locating C-RPs on a PE" has been
   taken almost verbatim from RFC3618.


20. References

20.1. Normative References

   [MVPN] E. Rosen, R. Aggarwal [Editors], "Multicast in MPLS/BGP IP
   VPNs", draft-ietf-l3vpn-2547bis-mcast-01.txt,

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

   [RFC2858] Bates, T., Rekhter, Y., Chandra, R., and D. Katz,
   "Multiprotocol Extensions for BGP-4", RFC 2858, June 2000.

   [RFC4364] E. Rosen, Y. Rekhter, "BGP/MPLS IP Virtual Private Networks
   (VPNs)", RFC4364, February 2006

   [RFC4360] Sangli, S., Tappan, D., and Y. Rekhter, "BGP Extended
   Communities Attribute", RFC 4360, February 2006.


20.2. Informative References

   [MPLS-UPSTREAM] R. Aggrwal, Y. Rekhter, E. Rosen, " MPLS Upstream
   Label Assignment and Context Specific Label Space", draft-ietf-
   mpls-upstream-label-00.txt

   [PIM-SM] B. Fenner et. al., "Protocol Independent Multicast - Sparse
   Mode (PIM-SM): Protocol Specification (Revised)", draft-ietf-pim-sm-
   v2-new-11.txt

   [RT-CONSTRAIN] P. Marques et. al., ",Constrained VPN Route
   Distribution" draft-ietf-l3vpn-rt-constrain-02

   [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-00



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21. Author Information

   Rahul Aggarwal
   Juniper Networks
   1194 North Mathilda Ave.
   Sunnyvale, CA 94089
   Email: rahul@juniper.net

   Eric C. Rosen
   Cisco Systems, Inc.
   1414 Massachusetts Avenue
   Boxborough, MA, 01719
   E-mail: erosen@cisco.com

   Thomas Morin
   France Telecom R & D
   2, avenue Pierre-Marzin
   22307 Lannion Cedex
   France
   Email: thomas.morin@francetelecom.com

   Yakov Rekhter
   Juniper Networks
   1194 North Mathilda Ave.
   Sunnyvale, CA 94089
   Email: yakov@juniper.net

   Chaitanya Kodeboniya



22. Intellectual Property Statement

   The IETF takes no position regarding the validity or scope of any
   Intellectual Property Rights or other rights that might be claimed to
   pertain to the implementation or use of the technology described in
   this document or the extent to which any license under such rights
   might or might not be available; nor does it represent that it has
   made any independent effort to identify any such rights.  Information
   on the procedures with respect to rights in RFC documents can be
   found in BCP 78 and BCP 79.

   Copies of IPR disclosures made to the IETF Secretariat and any
   assurances of licenses to be made available, or the result of an
   attempt made to obtain a general license or permission for the use of
   such proprietary rights by implementers or users of this
   specification can be obtained from the IETF on-line IPR repository at
   http://www.ietf.org/ipr.



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


23. Copyright Notice

   Copyright (C) The Internet Society (2006).

   This document is subject to the rights, licenses and restrictions
   contained in BCP 78, and except as set forth therein, the authors
   retain all their rights.

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





























Raggarwa                                                       [Page 45]


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