To prevent loops, router do not forward multicast out the same interface on which they were received. Multicast routers use a reverse path forwarding (RPF) check to prevent loops. A multicast router does not forward any multicast packet unless the packet passes the RPF check.
The issue of receiving duplicate packets, Cisco routers perform a reverse path forwarding (RPF)
Check to determine whether a multicast packet is entering a router on the correct interface
An RPF check examines the source address of an incoming packet and check it against the router’s uni-cast routing table to see what interface should be used to get back to the source network. If the incoming multicast packet is using that interface, the RPF check passes, and the packet is forwarded.
If the multicast packet is coming in a different interface, the RPF check fails, and packet is discarded.
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