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multicast route on Switch C and Switch D, and specify Switch B and Switch C as the RPF neighbors
of each other. Then, the receivers can receive multicast data that the multicast source sent.
NOTE:
•
Static multicast routes only affect RPF checks but cannot guide multicast forwarding.
•
A static multicast route is effective only on the multicast router on which it is configured, and is not
advertised throughout the network or redistributed to other routers.
Multicast forwarding across unicast subnets
Multicast data travels hop by hop along the forwarding tree from a multicast source to the multicast
receivers. However, some devices might not support multicast protocols. 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 or an IPv4 over IPv4 tunnel
between the devices at both ends of the unicast subnet.
For more information about GRE and tunneling, see
Layer 3—IP Services Configuration Guide
.
Figure 29 Multicast data transmission through a GRE tunnel
As shown in
, a GRE tunnel is established between Switch A and Switch B. Switch A
encapsulates multicast data in unicast IP packets. Unicast switches then forward the unicast IP
packets to Switch B across the GRE tunnel. When Switch B receives the unicast IP packets, it 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.
NOTE:
To make sure that the maximum transmission unit (MTU) feature operates properly in multicast
forwarding through GRE tunnels, configure the same MTU value for all Tunnel interfaces on an HPE
5820X switch or HPE 5800 switch. For more information about MTU configuration on a Tunnel
interface, see
Layer 3—IP Services Configuration Guide.
Multicast traceroute
You can use the multicast traceroute utility to trace the path that a multicast traffic flows down from
the first-hop router to the last-hop router.
