Switch A then sends its BPDU proposal with the IDB of the upper root switch to the IDB of Switch A. These switches are starting to replace the BPDUs configuration whose basic part is the proposal bit on one. If Port P0 gets the deal, Port P0 can immediately switch to transmission. Port P3, which was in a state of rejection after synchronization, is in exactly the same condition as Port P0 before receiving the agreement. Port P0 then begins to propose to its neighbor and tries to move quickly to the transmission. This handshake mechanism spreads rapidly to the edge of the network and quickly restores connectivity after a change in topology. In the past, timers were required to ensure that the port could participate in the transmission of the data, i.e. the swich passively waited for time to hear BPDU. The main feature of RSTP was the introduction of the port type concept based on the full duplex or semi-duplex mode (p2p or half-duplex) and the concept of a border port (a kind of p2p Edge) for terminals. The border ports are named by the Spanning-Tree-Portfast team as before, and everything is clear with them – if you turn on the wire right away, you enter the transport state and work. Common ports operate according to the old pattern with BLK – LIS – LRN – FWD-states. However, for p2p ports, RSTP uses the proposal and agreement process.

Without going into details, it can be described as follows: Swich rightly thinks that if the connection works in full duplex mode and it is not marked as borderline, it means that it has only two devices – it and another swich. Instead of waiting for the arrival of the BPDU, he tries to contact the swich at the other end of the line, using a special proposal from BPDU which, of course, has information about the cost of the route to the root.