Configure the core switch as root

To configure a core switch as the root bridge, adjust its STP priority to the lowest value using Cisco IOS commands, ensuring it is elected as the root for each VLAN.Steps to Configure the Root BridgeAccess the Switch CLIConnect to the core switch and enter privileged EXEC mode:CodeCopyenable Enter global configuration mode:CodeCopyconfigure terminal Set the Switch as Root BridgeFor a specific VLAN, you can configure the switch as the primary root bridge:CodeCopyspanning-tree vlan root primary This command automatically lowers the switch priority to ensure it becomes the root bridge for that VLAN .Alternatively, set the priority manually:CodeCopyspanning-tree vlan priority 4096 Lower priority values increase the likelihood of the switch being elected as root. If multiple switches have the same priority, the switch with the lowest MAC address becomes the root .Configure Secondary Root Bridge (Optional)To designate a backup root bridge:CodeCopyspanning-tree vlan root secondary This sets the switch priority slightly higher than the primary root, allowing it to take over if the primary fails .Enable Root Guard on Distribution/Access PortsTo prevent other switches from becoming the root bridge unexpectedly, enable root guard on ports connecting to lower-tier switches:CodeCopyinterface spanning-tree guard root Ports with root guard will enter a root-inconsistent state if a superior BPDU is received, protecting the core switch as the root .Verify ConfigurationCheck the root bridge status and STP topology:CodeCopyshow spanning-tree This command displays the root bridge for each VLAN, port roles, and priority values .Best PracticesPlace the root bridge on the most reliable and high-performance switch, typically the core switch, to optimize traffic flow .Use consistent priority values across VLANs to maintain predictable STP behavior.Enable root guard on distribution and access layer switches to prevent accidental or malicious root bridge changes .Document the STP configuration and monitor for topology changes regularly. By following these steps, you ensure that your core switch is the root bridge, providing a stable and efficient Layer 2 network topology.