When a switch detects a topology change, it sends a Topology Change Notification (TCN) BPDU toward the root. The root then sets a flag in its regular BPDUs telling all switches to shorten their MAC table aging time from seconds to the forward delay time. This flushes stale entries faster. Without this mechanism, traffic might go to the wrong ports for minutes after a failure. TCN handling ensures the network adapts quickly to link or switch failures.
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$ curl repovive.com/roadmaps/network-design/spanning-tree-and-link-aggregation/topology-change-notification
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