H3C Technologies H3C S10500 Series Switches - Manual (Page 95)

80
static 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:
•
A multicast static route only affects RPF check; it cannot guide multicast forwarding. Therefore, a
multicast static route is also called an “RPF static route”.
• A multicast static route is effective only on the multicast router on which it is configured, and will not be
advertised throughout the network or redistributed to other routers.
Application of GRE tunnel 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 29 Multicast data transmission through a GRE tunnel
GRE tunnel
Unicast router
Unicast router
Unicast router
Unicast router
Multicast router Multicast router
Switch A Source Receiver Switch B
As shown in Figure 29 , with a GRE tunnel established between Switch A and Switch B, Switch A
encapsulates multicast data in unicast IP packets, which unicast routers then forward to Switch B across
the GRE tunnel. Then, Switch 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 multicast
static route across the tunnel, so that only multicast packets are transmitted through this tunnel.
Multicast traceroute
You can use the multicast traceroute utility to trace the path that a multicast stream flows down from the
first-hop router to the last-hop router.