PIM SM pruning

PIM SM pruning
Router 5 receives an IGMP message requesting the removal of Host G from the group.
Because Host G was the last active member of the group, the (∗, G) entry is set to null 0 and a
prune request is sent by Router 5 to Router 3. When Router 3 receives the request, it removes
the link for interface S0 from the forwarding table. Because Host F is a directly connected active
member of the group, the entry for (∗, G) is not null 0, so no prune request is sent to Router 2
(the RP for this example).
If Host F were not active, the entry for (∗, G) would have been set to null 0 also and a prune
request would have been sent to the RP.