The spanning tree algorithm automatically detects the presence of legacy STP bridges on the
network, and falls back to STP mode when communicating with those bridges. Because legacy STP
bridges do not send spanning tree BPDUs periodically in all circumstances, the BIG-IP® system cannot detect when a legacy STP bridge is removed from the network.
Therefore, it is necessary to manually notify the BIG-IP system that the algorithm can switch to
the RSTP or MSTP protocol again, whenever a legacy bridge has been removed.