On each network segment, one port is the designated port. This is the port responsible for forwarding traffic from that segment toward the root. The switch with the lowest root path cost on that segment wins. If costs tie, the switch with the lower Bridge ID wins. All ports on the root bridge are designated ports because the root has a path cost of . Designated ports forward frames and send BPDUs. Every segment needs exactly one designated port to avoid loops.
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$ curl repovive.com/roadmaps/network-design/spanning-tree-and-link-aggregation/designated-port-selection
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