Reason for STP root bridge change on S series switch

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.

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