CCNA Foundations: STP Root Bridge by Design — Own the Election

Archive lab

CCNA exam domain: Network Access

Designate an intentional STP root bridge and backup for a campus user VLAN across a redundant three-switch triangle. You will verify correct root election and port roles and confirm end-to-end host connectivity while preventing Layer-2 loops.

Learning objectives

• Configure deterministic STP root/backup for a user VLAN using bridge priority or root primary/secondary macros
• Verify root bridge identity and per-port roles/states using show commands
• Validate end-to-end host connectivity across a redundant Layer-2 triangle while STP blocks loops
• Harden trunks with native VLAN separation and allow-lists to keep the topology clean

Troubleshooting focus

• If the wrong switch wins the election, check spanning-tree vlan <id> priority values and ensure your intended root has the numerically lowest bridge ID
• If a trunk blocks unexpectedly, verify matching native VLAN and allowed VLANs on both sides; mismatches can cause STP topology changes or user VLAN isolation
• If hosts can’t ping, ensure both access ports are in the same VLAN and are up; also confirm one uplink to the access switch is forwarding for the VLAN