BeginnerPublished 2026-08-25
CCNA Break/Fix: The Root Bridge Nobody Elected
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Lab 2 of 7 in CCNA Break/Fix: Diagnose and Repair · ← Previous · Next →
CCNA exam domain: Network Access
A campus triangle of one distribution and two access switches carries VLAN 10 and VLAN 20. After an access-switch replacement, users report slower cross-campus response: hosts still reach each other, and the layer 2 path no longer matches a design that roots both VLANs at SW-CAMPUS-DIST1.
Learning objectives
- Diagnose which switch holds root for each VLAN with
show spanning-tree. - Trace the VLAN 10 path from CLIENT10-A to CLIENT10-B and the blocked port.
- Distinguish an election result from a trunk inconsistency with
show interfaces trunk. - Verify both VLANs converge on the intended root and the blocked port moves.
Troubleshooting focus
- A distribution uplink blocks while the access-to-access link forwards. Compare Root ID on all three switches.
- Blocking shifts without an election change. Compare both trunk ends for VLANs 10, 20 and native VLAN 999 with
show interfaces trunk. - One VLAN's tree moves and the other does not. Rapid-PVST elects per VLAN; re-read both after every change.
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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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