If you are working in a service provider network then might be facing a problem of links flapping whic are attached towards the cpe. A very common issue which is always being ignored many times. But during the log analysis we always a weired error of receiving bpdu which smaller cost and most of the time we hardly diagnose the probelm. So eventually one of my collegaue added a command callled spanning-tree bpdufilter enable. After adding the command the link flapping stopped. After that we analysed what happened after adding the command, why the link flaping stopped suddenly and as soon as we removed we get stucked into the same. Actually from clinet end superior bpdu are receiving by the switch port and due to which port may be going in block state. After adding the command whenevve the switch receives the bpdu from clinet end it sliently drops it and issue resolved smartly.So we finalize make a best practise of adding the command to every client facing interface.