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If a router receives a multicast packet for which it has
state, either (S,G) or (*,G), on an outgoing interface, the router
knows another router is forwarding packets onto the network. For
example, the serial interfaces for both routers B and C are the RPF
interfaces back to the multicast source. When router A receives a
packet from the source, the packet is forwarded to both routers B
and C. With no other mechanism in place, both routers B and C will
forward the traffic to router D, creating duplicate packets on the
network. Assert messages are used to avoid this situation. |
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