How to prevent network flapping caused by changes of Eth-Trunk member interfaces on CE switches

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The path cost of Eth-Trunks change when Eth-Trunk member interfaces go Up or Down. In this case, STP recalculates the path cost and spanning tree, causing network topology changes and network flapping.
You can run the stp [ process process-id ] [ instance instance-id ] cost cost command in the Eth-Trunk interface view to set the path cost of Eth-Trunks to a fixed value. In this way, the changes of Eth-Trunk member interfaces do not affect the path cost, preventing network topology changes.
For example, set the path cost of Eth-Trunk 1 to 200.
system-view
[~HUAWEI] interface eth-trunk 1
[*HUAWEI-Eth-Trunk1] stp cost 200
[*HUAWEI-Eth-Trunk1] commit

Other related questions:
Setting the number of Eth-Trunk member interfaces on CE switches
Except that each Eth-Trunk on the CE5810EI supports a maximum of eight member interfaces, the maximum number of member interfaces on other switch models is configured using commands. For the CE12800 and CE6870EI: Run the assign forward eth-trunk mode { 256 | 512 | 1024 } command in the system view to set the number of Eth-Trunk member interfaces supported by the switch. By default, a maximum of 512 interfaces can be added to an Eth-Trunk on the switch. When 256 is specified, the switch allows a maximum of 256 LAGs and each LAG supports a maximum of 64 member interfaces. When 512 is specified, the switch allows a maximum of 512 LAGs and each LAG supports a maximum of 32 member interfaces. When 1024 is specified, the switch allows a maximum of 1024 LAGs and each LAG supports a maximum of 16 member interfaces. For CE8800&7800&6800&5800 series switches: Run the assign forward eth-trunk mode { 64 | 128 | 256 | 512 | 1024 } command in the system view to set the number of Eth-Trunk member interfaces supported by the switch. By default, a maximum of 128 interfaces can be added to an Eth-Trunk on the switch. When 64 is specified, the switch allows a maximum of 64 LAGs and each LAG supports a maximum of 32 member interfaces. When 128 is specified, the switch allows a maximum of 128 LAGs and each LAG supports a maximum of 16 member interfaces. When 256 is specified, the switch allows a maximum of 256 LAGs and each LAG supports a maximum of 8 member interfaces. When 512 is specified, the switch allows a maximum of 512 LAGs and each LAG supports a maximum of 4 member interfaces. When 1024 is specified, the switch allows a maximum of 1024 LAGs and each LAG supports a maximum of 2 member interfaces. Description: After the assign forward eth-trunk mode command is used to change the number of Eth-Trunk member interfaces supported by the switch, restart the switch to make the configuration take effect.

Load balancing principle of Eth-Trunk member interfaces on CE switches
An Eth-Trunk has 16 timeslots for sending packets at each interval. Eth-Trunk member interfaces use the 16 timeslots to send packets in sequence. When the number of Eth-Trunk member interfaces is the nth power of 2, load balancing can be made more even. For example, if the number of Eth-Trunk member interfaces is 2, 4, or 8 (which is divisible by 16), the timeslot of the packets sent by each interface is an integer, making load balancing even. If it is not the nth power of 2 (for example, 3), a member interface gets 6 times for sending packets from 16 timeslots, while the other two only get 5 times. In this way, load balancing is not even. Therefore, you are advised to set the number of Eth-Trunk member interfaces to the nth power of 2, ensuring even load balancing.

Number allocation of Eth-Trunk member interfaces on stacked S series switches
After you configure an Eth-Trunk on stacked S series switches (except the S1700), the member interface number remain unchanged even if you split the stack and stack the switches again.

How to determine the number of member interfaces in an Eth-Trunk
To ensure normal forwarding of burst traffic on an Eth-Trunk, the total bandwidth of the Eth-Trunk must be higher than the bandwidth of an interface that forwards normal traffic. To ensure that member interfaces of an Eth-Trunk evenly load balance traffic, you can use two, four, or eight member interfaces.

The type of Eth-Trunk member interfaces on S series switches
Observe the following guidelines when adding member interface to an Eth-Trunk on S series switches (except the S1700): 1. The member interface cannot be configured with some services or static MAC address entries. For example, when an interface is added to an Eth-Trunk, the interface must use the default link type. 2. An Eth-Trunk cannot be added to another Eth-Trunk. Member interfaces of an Eth-Trunk must use the same Ethernet type and rate. Interfaces that use different Ethernet types and rates cannot join the same Eth-Trunk. For instance, GE interfaces and FE interfaces cannot join the same Eth-Trunk, but GE electrical interfaces and GE optical interfaces can join the same Eth-Trunk. 3. Both devices of the Eth-Trunk must use the same number of physical interfaces, interface rate, duplex mode, and flow control mode. 4. If an interface of the local device is added to an Eth-Trunk, an interface of the remote device directly connected to the interface of the local device must also be added to an Eth-Trunk; otherwise, the two ends cannot communicate.

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