PIM routers without state-refresh messaging capability

A PIM router without a state-refresh messaging capability learns of currently active flows in a multicast network through periodic flood and prune cycles on the path back to the source. The switches covered in this guide sense downstream multicast routers that do not have the state-refresh capability and will periodically flood active multicast groups to these devices. This periodic flooding is not necessary if all downstream multicast routers are switches covered in this guide.