How to prevent slow convergence on STP edge ports connected to terminals

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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.

Other related questions:
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 can I configure edge ports and BPDU protection on an S series switch
User-side devices (such as servers) of a switch do not need to run STP. If STP is enabled on the switch ports connected to these devices, it takes some time for the ports to enter the forwarding state when the ports alternate between Up and Down states or the STP topology changes. This is unacceptable for some services. To solve the preceding problem, you can configure these ports as edge ports. Edge ports can enter the forwarding state immediately after they go Up, and they do not send TC packets and have no impact on services on the STP network. To configure a port as an edge port and enable the BPDU protection function on an S (except the S1700) or E series switch, perform the following operations: 1. Configure a port as an edge port to enable the port not to participate in spanning tree calculation. Run the stp edged-port enable command in the interface view. [HUAWEI] interface gigabitethernet 0/0/1 [HUAWEI-GigabitEthernet0/0/1] stp edged-port enable 2. Configure BPDU protection. After BPDU protection is enabled, the switch shuts down the edge port if the edge port receives a BPDU. The attributes of the edge port are not changed. Run the stp bpdu-protection command in the system view. [HUAWEI] stp bpdu-protection For other configuration commands, visit "Common STP/RSTP Operations" in Common Operation Guide to view the related document. Common STP/RSTP operations are the same for all switch models.

Configure STP on an interface of the S1728GWR-4P switch
Configure STP on an interface of an S1728GWR-4P switch as follows: 1. Choose Spanning Tree > STP. 2. Select Configure Interface from the Step drop-down list box. 3. Select Configure from the Action drop-down list box. 4. Configure the parameters such as Spanning Tree, Admin Link Type, Priority, and Admin Path Cost. 5. Click Apply.

Display STP configuration of an interface on the S1728GWR-4P switch
Display the STP configuration of an interface on an S1728GWR-4P switch as follows: 1. Choose Spanning Tree > STP. 2. Select Configure Interface from the Step drop-down list box. 3. Select Show Information from the Action drop-down list box. 4. The configured parameters (such as STP Status, Port Role, Designated Bridge, Oper Path Cost, and Oper Edge Port) are displayed.

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.

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