Working on the PIM NBMA mode lab where you have to configure ip pim nbma on r1's serial interface. I have configured everything correctly (I think) and r2 is not seeing the multicast traffic for sw2 and r5 is not seeing the multicast traffic for r4 which is correct. But, in order for me to get the traffic flowing correctly I had to configure the rp address on sw1 but r3 still had oil as null. When i added the rp address on both sw2 and r4, traffic started flowing. Am i missing something obvious?