In STP, the Root Bridge is identified by which criterion?

• A. The bridge with the most ports
• B. The bridge with the highest MAC address
• C. The oldest device
• D. The bridge with the lowest bridge ID

Answer: (D)

In STP, the Root Bridge is determined by the bridge ID, and the bridge with the lowest Bridge ID becomes the Root Bridge. The Bridge ID is made up of a configurable priority value plus the bridge’s MAC address. The lowest priority wins; if priorities are the same, the bridge with the lowest MAC address wins. This rule ensures a unique root bridge, which acts as the reference point for all path calculations in the spanning-tree.