Users Guide

1606 IPv4 and IPv6 Multicast
Figure 46-8. PIM-SM SPT—Part 5
• 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 de-
encapsulation 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 EMC Networking Optimizations to PIM-SM
Dell EMC 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.