MSTP Fast Convergence
Ordinary P/A
The ordinary P/A mechanism supported by MSTP is implemented in the same manner as that supported by RSTP. For details about the P/A mechanism supported by RSTP, see Technical Details of RSTP.
Enhanced P/A
As shown in Figure 10-10, in MSTP, the P/A mechanism works as follows:
The upstream device sends a proposal to the downstream device, indicating that the port connecting to the downstream device wants to enter the Forwarding state as soon as possible. After receiving this BPDU, the downstream device sets the port connected to the upstream device as a root port and blocks all non-edge ports.
The upstream device sends an agreement. After receiving this BPDU, the root port enters the Forwarding state.
The downstream device replies with an agreement. After receiving this BPDU, the upstream device sets the port connected to the downstream device as a designated port, and the designated port transitions to the Forwarding state.
By default, Huawei network devices use the fast transition mechanism in enhanced mode. To enable a Huawei network device to communicate with a third-party device that uses the fast transition mechanism in common mode, configure the Proposal/Agreement mechanism on the Huawei network device so that it works in common mode.