Why is the convergence for multiple MST regions slow


When a specified interface of the root bridge is faulty, the two packets that contain different root bridge information in an MST region may interact with each other continuously. The root bridge selection flaps for a period. As a result, the negotiation time is long and the network convergence is slow.

Using the stp max-hops command, you can properly limit the maximum number of hops as required. Thus, the root bridge can be quickly confirmed and the convergence time can be shortened.

Other related questions:
How do I determine whether devices belong to the same MST region
Check whether the region configurations on devices are the same. If so, the devices belong to the same Multiple Spanning Tree (MST) region. If not, the devices belong to different MSTP regions. For example, devices with the same region name, VLAN-instance mapping, and revision level belong to the same region.

How does an AR router determine a same MST region
The device fails to learn correct MAC entries because: - The device does not receive packets because a link is Down, an interface is not added to a VLAN, an interface joins in loop protocol calculation and is blocked, or the MAC address drift detection is configured and an interface or a MAC address is blocked. - There is a loop in the network, causing MAC entry flapping. - The MAC address learning function is disabled, or corresponding sticky MAC address already exists. - The number of MAC entries has reached the upper limit of the device. - A static or blackhole route is configured.

What is and how to implement STP slow convergence
STP slow convergence is a concept relative to the fast convergence of RSTP and MSTP point-to-point links. It is not a new function but the initial convergence mode of the STP protocol. The STP port is blocked by default. After the STP root bridge is selected and the port role calculation is performed, the port enters the listening state. After the first ForwardDelay, the status switches from listening to learning. This ForwardDelay takes 15 seconds, during which the port is in the listening state. After the second ForwardDelay, the status switches from learning to forwarding. This ForwardDelay takes 15 seconds, during which the MAC address learning is completed. The two ForwardDelay takes total 30 seconds during which STP port enters the forwarding process. This whole process is called slow convergence. NOTE: During the 30 seconds' slow convergence, the port is blocked, and the sent DHCP packets are discarded for multiple times, making the DHCP protocol run abnormally. In this case, modify configuration to prevent slow convergence.

How to prevent slow convergence on STP edge ports connected to terminals
Edge devices cannot participate in the STP calculation or respond to STP packets, causing slow convergence. You can use either of the following methods to prevent slow convergence on edge ports connected to user terminals or servers: 1. Run the stp disable command on the ports so that the ports always remain in the Forwarding state. 2. Run the stp edge-port enable command on the ports to configure them as edge ports, and then run the stp bpdu-protection command on the ports to enable BPDU protection. An edge port is in Forwarding state by default. The BPDU protection function shuts down an edge port after the port receives a BPDU. The edge ports that are shut down must be manually restored.

What is the function of an AP region
An AP region is a geographical scope in which APs are deployed. It is used for radio power adjustment to reduce interference or batch upgrade of APs of the same model in the same region. AP regions can be added, deleted, modified, and merged.

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