Troubleshooting Multicast RPF Failure in Data Plane

Loop prevention mechanism of multicast is to check the source IP with it's unicast routing table and do a RPF check (Reverse Path Forwarding). If the source is learned from the interface which the feed is received, the traffic is allowed to go through the router.

Let's take an example.

OSPF is configured for all links in routers but PIM is not enabled on E0/2 of R1 and R3.
What will happen is 192.168.1.0/24 will be learnt by R3 via OSPF from R1 but the multicast traffic will come from R2..

Let's join PC to the group 239.1.1.1

PC(config)#int e0/0
PC(config-if)#ip igmp join-group 239.1.1.1

Well the pings are failing..
Let's look at the multicast routing table,

It shows the incoming interface as Null and RPF neighbor as 0.0.0.0

Let's look at the unicast routing table for the 192.168.1.10 source.

Well there was a good debug command debug ip mpacket which should be used along with no ip mroute-cache interface level command to see rpf issues in multicast routing. Unfortunately Cisco has removed it from IOS version 15.0

But you can still check for RPF for the source using the following command.
R3#show ip rpf 192.168.1.10

Let's fix this issue by using a static mroute. First have to find the next-hop using following command.
R3#show ip pim neighbor

Now the command to route is;
R3(config)#ip mroute 192.168.1.10 255.255.255.255 192.168.23.2

As soon as the route entered, IPTV_Svr has replies,

Now let's see the routing tabe of R3;