RSTP's speed comes from the proposal-agreement mechanism. When a switch wants to make a port designated and forwarding, it sends a proposal in its BPDU. The downstream switch blocks all non-edge ports and sends back an agreement. The upstream switch immediately moves the port to forwarding. This happens in milliseconds, not seconds. No timer waiting. The synchronization ensures no temporary loops form. This peer-to-peer negotiation is why RSTP on point-to-point links converges so fast.
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$ curl repovive.com/roadmaps/network-design/spanning-tree-and-link-aggregation/rstp-proposal-agreement
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