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BeginnerPublished 2026-07-02

Spanning Tree Fundamentals: Root Election & Port Roles

Free preview — the first lab of Spanning Tree Protocol (STP)

Beginner CCNA lab on a redundant two-switch Layer-2 loop with two parallel uplinks. You will enable Rapid-PVST+, set a deterministic root-bridge priority so SW1 becomes the root for VLAN 1, and verify port roles (root/designated/alternate) and loop prevention. Two Alpine hosts in VLAN 1 validate end-to-end connectivity without any routing or SVIs.

Track
Est. time
45 minutes
Difficulty
Beginner
Topics

Learning objectives

  • Enable Rapid-PVST+ globally on Layer-2 switches
  • Deterministically elect the STP root by configuring bridge priority
  • Interpret RSTP port roles and states (root, designated, alternate/blocking)
  • Validate loop prevention with parallel inter-switch links
  • Use IOS show commands to confirm STP status per VLAN and interface

Troubleshooting focus

  • Wrong switch elected as root due to a lower bridge priority
  • Parallel inter-switch links both forwarding due to mode mismatch or disabled STP
  • Host-facing ports misconfigured as trunks or missing PortFast/BPDU Guard
  • Access VLAN mismatch between host-facing ports across closets

Topology

Lab topology diagram

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How this lab is graded
  • Build it your way. Where a lab lets you choose a value — a VLAN name, an interface description — grading checks that you configured it, not which name you picked. Names that another line has to reference, like an ACL applied with access-class, are stated in the guide and do have to match.
  • Addresses, modes and protocol keywords are exact. An IP address, a subnet mask, switchport mode trunk, an encapsulation — these carry the meaning of the lab, so they are graded as written in the guide.
  • Grading reads your saved configuration. Export the lab from CML after you have configured it, and make sure anything you set is in the running-config — a change that only exists in a terminal session never reaches the grader.
  • You can submit as many times as you like. Your best score stands, and each attempt tells you which checks passed so you can work the gaps.
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