Tom, You do not have to configure RPF. It is an automatic mechanism. It is part of PIM protocol. It is used to prevent loops. The interface that is considered the shortest path to the source does an RPF check. Kind of like Split Horizon.
When a router receives a multicast packet, it checks its routing tables (usually unicast) to see if the interface the packet came from provides the shortest path back to the source. If the interface provides the shortest path to the source, the router will forward the packet. Otherwise, if the multicast packet is received from some other interface that does not provide the shortest path to the source, it?s silently discarded. This mechanism that multicast routing utilizes is called Reverse Path Forwarding (RPF). RPF ensures that multicast packets will follow the shortest path from the source to the receivers and that there will be no loops on that path. After the router receives a multicast packet, it performs an RPF check. If the RPF check succeeds, the packet is forwarded; otherwise, it?s silently discarded. The multicast packet is forwarded out of each interface that is in the Outgoing Interface List (OIL). OIL entries point to the current router?s downstream multicast neighbors. The incoming interface (or RPF interface) on which the packet was received is never in the OIL; therefore, the packet is never forwarded back out of the RPF interface. Hope this helps! Regards, Dan Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=39115&t=36941 -------------------------------------------------- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
