Reason for STP root bridge change on S series switch

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An S series switch (except S1700 switches) with the smallest bridge ID (BID) is elected as the root bridge. A BID consists of a 16-bit bridge priority and a bridge MAC address.
If bridge priority is not specified manually, the switch with the smallest MAC address will become the root bridge.
After topology calculation is complete, if the root bridge receives packets carrying a smaller BID than its own BID, the root bridge is no long the root bridge and the topology of the entire network must be recalculated.
If this occurs, run the stp root primary command to assign the lowest priority to a switch so that this switch becomes the root bridge.

Other related questions:
Display global STP configuration of the S1728GWR-4P switch
Display the global STP configuration of an S1728GWR-4P switch as follows: 1. Choose Spanning Tree > STP. 2. Select Configure Global from the Step drop-down list box. 3. Select Show Information from the Action drop-down list box. 4. The configured parameters (such as Spanning Tree Status, Spanning Tree Type, Designated Root, Root Path Cost, and Bridge ID) are displayed.

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.

Is STP enabled on S series switches by default
For Sx700 series switches (except the S1700) running V100R005 or an earlier version, STP is disabled globally by default, and STP on interfaces is enabled by default. For Sx700 series switches (except the S1700) running V100R006 or a later version, STP is enabled globally and on interfaces by default. For E series switches, STP is enabled globally and on interfaces by default. For S9300 series switches, STP is disabled globally by default, and STP on interfaces is enabled by default. For S5700 switches running V100R005, BPDU is disabled by default, and an interface discards received BPDUs by default. To enable BPDU, run the following commands: [HUAWEI] stp enable [HUAWEI] interface GigabitEthernet 0/0/1 [HUAWEI-GigabitEthernet0/0/1] bpdu enable

Checking the restart reasons of an S series switch
the display reboot-info command to check restart reasons of S series switches (except S1700 switches). A switch may be restarted due to one of the following reasons: MANUAL: It is restarted by using the reboot command. POWER: It is restarted after being powered off. SCHEDU: It is restarted by using the schedule reboot command. OTHER: It is restarted due to either of the following reasons: 1. It is power recycled instantly, for example, the power cable is in bad contact or transient overvoltage and loss of voltage occurs. In this case, check whether the power cable is correctly connected to the switch. 2. An exception occurs in the system.

If SCHEDU or MANUAL is displayed in the command output, the switch is normally restarted. If POWER or OTHER is displayed, check whether any other devices using the same power supply system have reboot records around the time when the switch is restarted. If such reboot records are found, the switch's restart is caused by exceptions in the external power supply system. If no such reboot record is found, go to the next step . If the switch uses pluggable power modules, replace the power modules with power modules that can work normally to determine whether the power modules are faulty. If the switch uses built-in power modules, collect required information and contact Huawei technical support personnel if the external power supply system works properly. The information includes the outputs of the display version, display device, display reboot-info, display alarm urgent, and display power commands. (If pluggable power modules are used, the output of the display power command is not required.)


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