Cisco ASR 9000 Series Software Manual page 40

PE-PE Ingress Replication
• PE-PE ingress replication
• Dynamic P2MP-TE tunnels
• Flexible allocation of P2MP-TE attribute-sets
• Data and partitioned MDT knobs
• Multi-instance BGP support
• SAFI-129 and VRF SAFI-2 support
• Anycast-RP using MVPN SAFI
PE-PE Ingress Replication
The ingress PE replicates a C-multicast data packet belonging to a particular MVPN and sends a copy to all
or a subset of the PEs that belong to the MVPN. A copy of the packet is tunneled to a remote PE over a Unicast
Tunnel to the remote PE.
IR-MDT represents a tunnel that uses IR as the forwarding method. It is usually, one IR-MDT per VRF, with
multiple labeled switch paths (LSP) under the tunnel.
When PIM learns of Joins over the MDT (using either PIM or BGP C-multicast Routing), it downloads IP
S,G routes to the VRF table in MRIB, with IR-MDT forwarding interfaces. Each IR-MDT forwarding interface
has a LSM-ID allocated by PIM. Currently, LSM-ID is managed by mLDP and can range from 0 to 0xFFFFF
(20-bits). For IR, the LSM-ID space is partitioned between mLDP and IR. For IR tunnels, the top (20th) bit
is always be set, leading to a range of 0x80000 to 0xFFFFF. mLDP's limit is 0 to 0x7FFFF.
MVPN over GRE
A unicast GRE tunnel could be the accepting or forwarding interface for either a mVPN-GRE VRF route or
a core route. When multicast packets arrive on the VRF interface with the intent of crossing the core, they are
first encapsulated with a multicast GRE header (S,G) which are applicable to the VRF's MDT. Then, before
the packets are actually forwarded , they are encapsulated in a unicast GRE header. The (S,D) in this packet
are the origination and termination addresses for the unicast GRE tunnel.
GRE tunnel stitching is when both the accepting and forwarding interfaces are unicast GRE tunnels. Here,
the packet has two GRE encaps. The outer encap is the unicast header for the GRE tunnel. The inner encap
is the multicast GRE header for the MDT. This is called as double encap. There is a loss in terms of both
bandwidth and throughput efficiency. The bandwidth efficiency loss is because 48 bytes of encap headers are
being added to the original (VRF) packet. The throughput efficiency loss is the result of the processing time
required to apply two encaps.
For the mVPN-GRE, if the VRF interface is a GRE tunnel, the protocol packets received from LPTS will be
accompanied with the receiving unicast GRE tunnel interface and the VRF id of the VRF in which the GRE
tunnel is configured. Thus VRF specific processing can be done on the packet.
Restrictions
• MVPN over GRE is supported only on ASR 9000 Enhanced Ethernet LCs.
Cisco ASR 9000 Series Aggregation Services Router Multicast Configuration Guide, Release 5.1.x
40
Implementing Layer-3 Multicast Routing on Cisco IOS XR Software