BeginnerPublished 2026-08-24
CCNA Break/Fix: The Trunk That Carries Only Some VLANs
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Lab 1 of 7 in CCNA Break/Fix: Diagnose and Repair · Next →
CCNA exam domain: Network Access
Your team supports a small campus access layer: two switches, one 802.1Q trunk. The help desk reports VLAN 20 users cannot reach their peers while VLAN 10 users can, and both ends read up and trunking. Campus design: VLANs 10 and 20 are the only VLANs any trunk carries; every trunk's native VLAN is 999.
Learning objectives
- Diagnose a trunk that forwards one VLAN and drops another
- Isolate where a trunk's operational state departs from the campus design using show interfaces trunk
- Distinguish an access-port VLAN error from a trunk problem presenting the same symptom
- Verify every trunk parameter agrees at both ends of the link
Troubleshooting focus
- One VLAN crosses the link and the other does not: read
show interfaces trunkat each end against the campus design. - If a console logs an inter-switch mismatch, compare the two ends'
show interfaces trunkoutput value by value. - A host fails while its access port shows up/up: link state does not prove forwarding, so check the port's access VLAN and
show port-security.
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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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