CCNA Lab 4: Native VLAN Mismatch Troubleshooting

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Diagnose and remediate a trunk misconfiguration between an access switch and a distribution switch so that same-VLAN hosts across two access switches can communicate end-to-end. Use CDP and trunk verification commands to investigate the fault and restore proper trunk operation, without introducing any Layer-3 routing.

Learning objectives

• Identify a native VLAN mismatch using CDP neighbor details
• Explain untagged/native VLAN behavior on 802.1Q trunks
• Align native VLANs consistently across trunk endpoints
• Verify trunk state, native VLAN, and allowed VLAN lists
• Validate same-VLAN host connectivity across multiple access switches

Troubleshooting focus

• Use show cdp neighbors detail to detect native VLAN mismatches
• Correlate show interfaces trunk and show interfaces switchport to confirm native and allowed VLANs
• Test end-to-end reachability from the hosts before and after the fix