When a designated fault sport does not get an agreement after a proposal is submitted, it slowly switches to the redirect state and builds on the traditional 802.1D list learning sequence. This can occur if the remote bridge does not include the RSTP-BPDUs or if the remote bridge port is blocked. ■ Bits 1 and 6 are used for the proposal and unification process. On the link between S4 and S2, the fa0/2 of the S4 is the designated port, while the Fa0/2 of the S2 is the root port, so the S2 cannot send suggestions about this connection. The correct sequence of events is therefore that the S4 sends a proposal to the S2 and responds with S4`s agreement after blocking all its non-edge ports. As soon as SW1 gets SW2`s approval, it will immediately put its fa0/14 interface into redirection mode. 1.) The proposal/agreement process between S4 and S2 should go in the opposite direction. It is currently demonstrated that the S2 sends a proposal to the S4 and responds to S4 with an agreement. It`s not true. A proposal can only be sent from a designated port with a “Discarding” or “Learning” status, as described in the Cisco Understanding Rapid Spanning Tree Protocol on RSTP, PVST, and MSTP, all of which use the Rapid Transition Mechanism to speed up port forwarding for edge ports, root ports, and designated ports. The Rapid Transition Mechanism for designated ports is also referred to as the proposal/agreement (P/A) _transition. Your explanation is great.
I just have a doubt, is the root bridge chosen before the proposal/deal handshake process? If so, why is the BPDU proposal called SUPERIOR BPDU? • The next downstream switch will see the top BPDU and its non-edge ports will be transferred to designated states and rejections, allowing the proposal/agreement process to be restarted. 2.) Unlike animation, the proposal/agreement process between S2 and S3 does not take place at all. It is true that S2 can send a proposal to S3. However, S3 and S2 have already chosen another root port and the arrival of BPDU on both sides does not change this selection. This means that the connection between S2 and S3 must be blocked, otherwise a loop will be created that would pass through these two switches. In contrast, a proposal/agreement process is used to quickly put a connection into redirect mode. Therefore, even if S2 or S3 sends a proposal to its neighbor, no agreement should be sent, because the connection between S2 and S3 must remain blocked. Once p0 gets this agreement, it can immediately switch to the redirect state. This is step 4 in the previous figure.
Note that the p3 port remains in a certain state of failure after synchronization. In step 4, this port is in exactly the same situation as port p0 in step 1. He then begins to make a proposal to his neighbor and tries to quickly move to the state of transmission. – After the reciprocal exchange of BPDUs, which eventually contain suggestions, each switch will be aware of the fact that the link must remain blocked, because the root port of both switches will not be changed. Therefore, after exchanging bpDUs on the link between S2 and S3, it is immediately clear which port is the designated and which is the alternative port on that connection.