3.3. Protecting Spanning Tree

STP primarily uses BPDUs to ensure that the switch network is maintained loop free. When all is working well, STP should maintain the topology of the network. As you know, this happens for the most part on its own. There can be times, however, when this harmony can be interrupted. Some ports like edge or PortFast ports should never receive any BPDUs. If they do receive BPDUs, this could mean that a loop as been formed in the network, which would, to say the least, make your network operate undesirably. Now on the flip side, when ports that should be receiving BPDUs stop receiving BPDUs, STP can again make decisions, like unblocking a port that should still be blocked, that would have your network create a loop and ...

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