STP and RSTP Explained: Spanning Tree for the Network+ Exam
Spanning Tree Protocol exists to solve a problem that redundancy creates. You want more than one path between switches so the network survives a failed link. But Ethernet has no mechanism to stop a frame circulating forever, and more than one path means loops. STP deliberately blocks redundant links so the topology is loop-free, and unblocks them the moment the primary path fails. Why a Loop Is So Destructive Three things go wrong simultaneously, and they compound. Broadcast storms. An IP packet has a TTL field that kills it after enough hops. An Ethernet frame has nothing of the sort. A broadcast entering a loop is forwarded endlessly, and each switch duplicates it out every port, so traffic multiplies rather than merely circulating. Link utilization reaches 100% within seconds. MAC address table instability. The same source MAC arrives on different ports repeatedly, so switches rewrite their tables constantly and forwarding becomes unpredictable. Multiple frame deliver...