Dell N3200-ON Networking N-Series Switches User Guide version 6.8.0 - Page 1568

Figure 46-8. PIM-SM SPT-Part 5 RP Source First-Hop Traffic Flow Shared Tree Source Tree (S, G) traffic flow is now only flowing to the Receiver via a single branch of the Source Tree. DR Receiver • As a result of the SPT-Switchover, (S, G) traffic is now flowing only from the first-hop router to the last-hop router and from there to the receiver. Notice that traffic is no longer flowing to the RP. The PIM standard requires support for multi-hop RP in that a router running PIM can act as an RP even if it is multiple router hops away from the multicast source. This requires that the first-hop router perform encapsulation of the multicast data and forward it as unicast toward the RP. In practice, this encapsulation is almost always performed in software due to the complexity of the operation. Likewise, the RP must perform deencapsulation and forwarding of the multicast packets in software. This creates a performance problem in that it limits the number of packets that can be processed and places a high load on the CPUs in the first hop and RP routers, which can then adversely affect other router functions. Dell Networking Optimizations to PIM-SM Dell Networking N-Series switches perform the following optimizations to reduce the impact of multicast encapsulation/de-encapsulation and provide a higher level of multicast performance in the network. 1568 IPv4 and IPv6 Multicast