Rapid Spanning Tree Protocol (RSTP) | 529
Usage
Information
By default FTOS implements an optimized flush mechanism for RSTP. This helps in flushing MAC 
addresses only when necessary (and less often), allowing for faster convergence during topology 
changes. However, if a standards-based flush mechanism is needed, you can turn on this knob 
command to enable flushing MAC addresses after receiving every topology change notification.