Users Guide

Instead of continuing to use the SPT to the RP and the RPT toward the receiver, a direct SPT is created between the source
and the receiver in the following way:
1. Once the receiver DR receives the first multicast packet from the source, the DR sends a PIM join message to its RPF
neighbor.
2. The source DR receives the PIM join message, and an additional (S, G) state is created to form the SPT.
3. Multicast packets from that particular source begin coming from the source DR and flowing down the new SPT to the
receiver DR. The receiver DR is now receiving two copies of each multicast packet that is sent by the source - one from the
RPT and one from the new SPT.
4. To stop duplicate multicast packets, the receiver DR sends a PIM prune message toward the RP router, letting it know that
the multicast packets from this particular source coming in from the RPT are no longer needed.
5. The RP router receives the PIM prune message, and it stops sending multicast packets down to the receiver DR. The
receiver DR is getting multicast packets only for this particular source over the new SPT. However, multicast packets from
the source are still arriving from the source DR toward the RP router.
6. To stop the unneeded multicast packets from this particular source, the RP router sends a PIM prune message to the source
DR.
7. The receiver DR now receives multicast packets only for the particular source from the SPT.
1060
Multicast