A Critical Note On Ring Flushing

Rapid Spanning Tree Protocol enable switches to flood incoming frame with broadcast orunknown unicast destination address even in switched Ethernet networks having redundant links.It also allows switches to secretly learn location of connected devices in such networks. Howeversome of those learnt location may become stale if a topology change is detected by RSTP andneed to be flushed by switches in the network. It is found that standard address flushingtechnique of RSTP flushes too many addresses from large number of switches after a topologychange. As a result there is a sudden massive increase in flooding traffic which may causenetwork-wide congestion, frame delay and frame loss. Recently a new address flushing techniquenamed as Ring Flushing was proposed for RSTP that flushes addresses from small number ofselective ports of very selective switches and so dramatically reduces the amount of floodingtraffic after a topology change. However, numbers of flaws are identified in the currentimplementation of this newly proposed technique. This paper will not critically discuss the flaws inthe current implementation of Ring Flushing but will also propose there simple yet effectivesolutions.