Native Multicast - Cisco ASR 9000 Series Configuration Manual

Implementing Layer-3 Multicast Routing on Cisco IOS XR Software
MVPN over GRE
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.

Native Multicast

GRE tunneling provides a method to transport native multicast traffic across a non-Multicast enabled IP
network. Once the multicast traffic in encapsulated with GRE, it appears as an IP packet to the core transport
network.
A GRE tunnel can be a forwarding interface when the router is the imposition (or encap) router for that GRE
tunnel. The imposition router must prepend a unicast IPv4 header and GRE header to the multicast packet.
The source and destination IPv4 addresses for the added header are determined by the user configuration of
the tunnel. The newly encapsulated packet is then forwarded as a unicast packet.
When a GRE tunnel is an accepting interface for a multicast route, the router is the disposition (or decap)
router for the tunnel. The outer IPv4 header and GRE header must be removed to expose the inner multicast
packet. The multicast packet will then be forwarded just as any other multicast packet that arrives on a
non-tunnel interface.
Forwarding behavior
Cisco ASR 9000 Series Aggregation Services Router Multicast Configuration Guide, Release 6.0.x
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