Maintaining the prune state

For a multicast group "X" on a given VLAN, when the last host belonging to group "X" leaves the group, PIM places that VLAN in a prune state; this means that the group "X" multicast traffic is blocked to that VLAN. The prune state remains until a host on the same VLAN issues a join for group "X", in which case the router cancels the prune state and changes the flow to the forwarding state.