Application Of Gre Tunnel In Multicast Forwarding - 3Com S7906E Configuration Manual

Figure 1-3 Creating an RPF route
As shown in Figure
When no multicast static route is configured, the hosts (Receivers) in the OSPF domain cannot receive
the multicast packets sent by the multicast source (Source) in the RIP domain. After you configure a
multicast static route on Router C and Router D, specifying Router B as the RPF neighbor of Router C
and specifying Router C as the RPF neighbor of Router D, the receivers can receive multicast data sent
by the multicast source.
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

There may be routers that do not support multicast protocols in a network. As multicast traffic from a
multicast source is forwarded hop by hop by multicast routers along the forwarding tree, when the
multicast traffic is forwarded to a next-hop router 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 router resides by establishing a generic routing encapsulation (GRE) tunnel
between the routers at both ends of the unicast subnet.
For details about GRE tunneling, refer to GRE Configuration in the VPN Volume.
1-3, the RIP domain and the OSPF domain are unicast isolated from each other.
1-5