H3C Technologies H3C S12500 Series Switches - Manual (Page 79)

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multicast route on Switch C and Switch D, specifying Switch B as the RPF neighbor of Switch C and
specifying Switch C as the RPF neighbor of Switch D, the receivers can receive multicast data that the
multicast source sent.
NOTE:
•
Static multicast routes affect only RPF checks and they cannot guide multicast forwarding.
• A static multicast route takes effect only on the multicast router on which it is configured, and will not be
advertised throughout the network or redistributed to other routers.
GRE tunnel application in multicast forwarding
Some networking devices might not support multicast protocols in a network. Multicast devices forward
multicast traffic from a multicast source hop by hop along the forwarding tree. When the multicast traffic
is forwarded to a next-hop device that does not support IP multicast, the forwarding path is blocked. In
this case, you can enable multicast traffic forwarding across the unicast subnet where the
non-multicast-capable device resides by establishing a GRE tunnel between the devices at both ends of
the unicast subnet.
For more information about GRE tunneling, see Layer 3—IP Services Configuration Guide.
Figure 26 Multicast data transmission through a GRE tunnel
As shown in Figure 26 , with a GRE tunnel established between Device A and Device B, Device A
encapsulates multicast data in unicast IP packets, which unicast routers then forward to Device B across
the GRE tunnel. Then, Device B strips off the unicast IP header and continues to forward the multicast data
down toward the receivers.
If unicast static routes are configured across the tunnel, any unicast packet can be transmitted through the
tunnel. If you want to dedicate this tunnel to multicast traffic delivery, you can configure only a static
multicast route across the tunnel, so that only multicast packets are transmitted through this tunnel.
Multicast traceroute
The multicast traceroute utility traces the path that a multicast stream flows down from the first-hop router
to the last-hop router.