What are the two methods of ensuring that the RPF check passes? (Choose two)

What are the two methods of ensuring that the RPF check passes? (Choose two)
A . implementing static mroutes
B . implementing OSPF routing protocol
C . implementing MBGP
D . disabling the interface of the router back to the multicast source
E . disabling BGP routing protocol

View Answer

Answer: AC

Explanation:

The router determines the RPF interface by the underlying unicast routing protocol or the dedicated multicast routing protocol in cases where one exists. An example of a dedicated multicast routing protocol is MP-BGP. It is important to note that the multicast routing protocol relies on the underlying unicast routing table. Any change in the unicast routing table immediately triggers an RPF recheck on most modern routers.

Having OSPF routing protocol in place won’t really ensure that the RPF check passes.

Let’s say we have implemented OSPF routing protocol within the topology below (have a look at the URL

below), “R3” knows the best path to 1.1.1.0/24 is via interface F0/0 but “R3” receives multicast packet from source server (1.1.1.1/24) on interface S0/0. The RPF will fail. We can get this fixed by implementing static mroutes (static multicast-routes) to force multicast traffic to go back via interface S0/0 (ip mroute 0.0.0.0 0.0.0.0 s0/0)

Having unicast routing protocol (OSPF, EIGRP, BGP, RIP, IGRP, IS-IS etc) won’t necessarily mean the RPF will succeed but having a multicast routing protocol (Multipoint BGP) or dedicated multicast static routes (mroutes) will. The only which I still have is that if the multicast

routing protocol relies on the underlying unicast routing table (OSPF) how does it ensure that the RPF check passes.

https://supportforums.cisco.com/t5/network-infrastructure-documents/multicast-rpf-recovery-using-staticmulticast-routing/ta-p/3139007