CCNA: STP Port Cost & Priority — Steer the Blocked Link

Today's daily lab

Influence a downstream access switch’s STP root-port choice using per-interface path cost and port priority. You will make the access switch prefer the non-default uplink so that the intended link forwards while the other becomes the alternate/blocking path. Validate with show commands and end-to-end host pings.

Track

CCNA

Est. time

45 minutes

Difficulty

Intermediate

Topics

CCNA, Switching, STP, Path Selection

Learning objectives

Interpret PVST+ root bridge placement and current port roles

Influence a downstream switch’s root-port selection with per-interface spanning-tree cost

Optionally refine tie-breaks using spanning-tree port-priority

Verify the resulting forwarding and alternate/blocking ports and confirm end-to-end connectivity

Troubleshooting focus

If the root-port doesn’t move, ensure the modified interface’s spanning-tree cost was applied to the correct VLAN and correct interface

Confirm trunks are actually trunks on both ends with matching allowed VLAN list and native VLAN

Check for BPDU-related err-disable on access ports; clear if needed and correct any mis-cabling

Use show spanning-tree vlan 10 detail to compare root path cost on each uplink

Topology

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What's included in the package

Work / baseline CML import — lab-work.yaml

Topology diagram — topology.svg

Print-ready topology diagram (PDF) — topology.pdf

Step-by-step learner guide (Markdown — for Obsidian/VS Code) — lab-guide.md

Branded PDF lab guide — open in any viewer (Adobe/Preview) — lab-guide.pdf

Getting-started README — README.md

Verification checklist — verification-checklist.md

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.
Scored something you believe is correct? Use Report an issue on this page — that is exactly how the grading fixes in the changelog got found.

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CCNA: STP Port Cost & Priority — Steer the Blocked Link

Learning objectives

Troubleshooting focus

Topology

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