Remember the spanning-tree port states? We have a block, listening, learning and port state transmission. This is the first difference between the clamping shaft and the fast-tightening shaft. Rapid spanning-tree has only three port states: SWB will put all their ports in the state of rejection and send its own BPDU proposal to its neighbors downstream, if it receives a response from its neighbors downstream, it will put the passage from its base port to the transfer state and send a BPDU agreement to SWA to 1 and the proposal bit set at 0 . SWA ports will switch to redirection. The mechanism of the proposal agreement is very fast, because it does not rely on the lap times. This wave of handshakes spreads rapidly to the edge of the network and quickly restores connectivity after a change in topology. If a designated rejection port does not get an agreement after sending a proposal, it slowly switches to the transmission state and refers to the traditional 802.1D listening sequence. This can happen if the remote RSTP-BPDUs bridge does not include or if the remote bridge port is blocked. The explanation is great.
I have only one doubt, will the root bridge be chosen before the procedure of seizing the hand of the proposal/agreement? If so, why is the BPDU proposal called a superior BPDU? The port of SWB to SWA is the base port and refers an agreement to SWA. This starts the synchronization process in which the classic clamping shaft uses a Max-Age timer (20 seconds) for BPDUs before they are rejected. The fast clamping shaft works differently! BPDUs are now used as a keepalive mechanism, much like using routing protocols such as OSPF or EIGRP. If a switch misses three BPDUs from a nearby switch, it is assumed that the connection to that switch has been lost, and all MAC addresses are immediately deleted. There is only one thing the switches need to do. If a port switches to redirect state in RSTP, it means there is a change in topology. Note that in 802.1w (RSTP), this is the only thing that triggers the topology change process now. In the former 802.1D-Spanning-Tree, a TCN was created when a port switched to redirect mode or switched from learning or transmitting to blocking mode.
However, in RSTP, the topology change process is only generated when a port goes into redirect mode. In addition, the BPDU TCN is no longer used if the network only operates 802.1w. RSTP now uses only one type of BPDU, the BPDU configuration, for everything. So, when changing topology, it only sends a configuration BPDU with the TC bit set to draw the attention of other switches to the fact that a topology port has been moved to the transmission state.