Pick the root bridge
Three switches in a triangle all run default settings, so the switch with the lowest MAC address became the root bridge. Take control: run Rapid PVST+ on all three switches, make SW1 the root bridge for VLAN 1 and SW2 the backup root, using the root primary/secondary commands.
How it works: this is VulnTech NetLab, a network simulator running in your browser. Click a device in the diagram to open its console and type commands, just like on real equipment (? shows help, Tab finishes a word). Click a cable to inspect it. Tasks tick themselves off as you complete them; questions are answered in the box under each task. Your work is kept if you reload; Reset starts the network over.
Solution explanation
With equal priorities, SW3 won on MAC address. root primary set SW1 to 24576, lower than everyone else's 32768, so SW1 became root; root secondary set SW2 to 28672, so it takes over if SW1 fails. SW3's root port is now Gi0/1, its direct link to SW1 (cost 4).
Show solution
[SW1]
enable
configure terminal
spanning-tree mode rapid-pvst
spanning-tree vlan 1 root primary
end
[SW2]
enable
configure terminal
spanning-tree mode rapid-pvst
spanning-tree vlan 1 root secondary
end
[SW3]
enable
configure terminal
spanning-tree mode rapid-pvst
end
show spanning-tree vlan 1