In Spanning Tree Protocol, what determines the root bridge?

• A. The bridge with the highest MAC address.
• B. The bridge with the lowest bridge ID; It uses priority and MAC.
• C. The bridge that is physically closest to the center.
• D. The bridge with the most ports.

Answer: (B)

In Spanning Tree Protocol, the root bridge is the switch with the lowest Bridge ID. The Bridge ID is a combination of a configurable priority value and the switch’s MAC address, so the decision first compares priorities and, if those are tied, uses the MAC address as the tie-breaker. Because of this, the root bridge is determined by which device presents the smallest Bridge ID, not by physical proximity or how many ports it has. The default priority is adjustable (for example, to influence which switch becomes root); if two switches share the same priority, the one with the lower MAC address wins. The root bridge serves as the reference point for all path calculations, and other bridges select their root ports accordingly.