In Spanning Tree, on any given VLAN there can only be one Root. In order to determine which switch becomes the root, Spanning Tree holds an election to determine which switch becomes the root.
- Each switch begins by creating and sending an STP Hello BPDU message, claiming that itself is the root switch.
- If a switch hears a superior Hello better than it’s own Hello that contains a lower RBID, it stops claiming that its the root on its own BPDUs and starts forwarding the better BPDU to all other switches.
- Eventually all switches receive the superior BPDU and that switch wins the election.