IntermediatePublished 2026-07-28
CCNA: STP Port Cost & Priority — Steer the Blocked Link
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CCNA exam domain: Network Access
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.
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
- Make tie-breaks deterministic with 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
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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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