200-301: Cisco Certified Network AssociateDemo

Spanning Tree Protocol selects the root bridge based on the Bridge ID, which consists of priority and MAC address. The switch with the lowest priority value becomes root; if priorities are equal, the switch with the lowest MAC address wins. SW1 and SW2 both have priority 20480 (lower than SW3 and SW4 at 57344), but SW2's MAC address 00:10:a1:54:4e:50 is numerically lower than SW1's 00:10:a1:71:e3:35, making SW2 the root bridge.