Fw: Multicast in BGP/MPLS VPN with pseudo wires technology

[xuxiaohu 41208 <xuxh at huawei.com>]

Hi,Spener,

Thanks for your professional comments first:)
   
As you mentioned in your last email, draft-ietf-l3vpn-2547bis-mcast-00 exactly mentioned that MPLS can be used as unicast tunnel for ingress replication .The following detailed description of demultiplexor is included in section 6.1.1 and section 11.3 of the above draft:
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6.1.1. Auto-Discovery for Ingress Replication

   In order for a PE to use Unicast Tunnels to send a C-multicast data
   packet for a particular MVPN to a set of remote PEs, the remote PEs
   must be able to correctly decapsulate such packets and to assign each
   one to the proper MVPN. This requires that the encapsulation used for
   sending packets through the tunnel have demultiplexing information
   which the receiver can associate with a particular MVPN.

   Thus an ingress PE must not transmit C-multicast data through a
   particular kind of unicast tunnel to a particular remote PE unless it
   knows that the remote PE has supports that particular tunnel
   encapsulation, and unless there is some agreement between the two PEs
   as to what values of the demultiplexing information represent which
   MVPNs.  If a PE is capable of ingress replication for an MVPN, it
   announces this as part of the BGP based MVPN membership auto-
   discovery process, described in section 4. The following information
   elements need to be advertised by a PE:

      1. The ability to support ingress replication for a particular
         MVPN, using a particular encapsulation format (e.g., MPLS,
         MPLS-in-GRE).

      2. A mapping of demultiplexing values to MVPNs.

         If the encapsulation format is MPLS or MPLS-in-something, the
         demultiplexing values may be downstream-assigned MPLS labels.
         The encapsulation procedures are described further in section
         11.

11.3. Encapsulations for Unicasting PIM Control Messages

   When PIM control messages are unicast, rather than being sent on an
   MI-PMSI, the the receiving PE needs to determine the particular MVPN
   whose multicast routing information is being carried in the PIM
   message.  One method is to use a downstream-assigned MPLS label which
   the receiving PE has allocated for this specific purpose.  The label
   would be distributed via BGP.  This can be used with an MPLS, MPLS-
   in-GRE, or MPLS-in-IP encapsulation.

   A possible alternative to modify the PIM messages themselves so that
   they carry information which can be used to identify a particular
   MVPN, such as an RT.

   This area is still under consideration.
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>From the above descriptions, we can not determine that a PE assigned different labels as demultiplexor for special MVPN to different PEs within the same MVPN. On the contrary, the label is only a demultiplextor for MVPN in egress PE and is unrelated to ingress PE. So the egress PE can not determine ingress PE from which the received packet is transmitted just from the demultiplextor label.

So the ingress PE's address should be carried in multicast data packets with MPLS-in-GRE or MPLS-in-IP encapsulation, or the TE tunnel with PHP off between PEs can also determine the ingress PE. 

The reason that MPLS-in-GRE or MPLS-in-IP encapsulation is not prefered in my method of implementing ingress replication is the encapsulation and decapsulation efficiency is low relatively. 


Regard
Steven Joe 
Huawei Technologies Co.,Ltd. 
Email: xuxh at huawei.com 

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