I’m facing a strange issue with VLAN tagging on trunk ports after a power fluctuation. The setup includes multiple Cisco switches (mainly Catalyst series), with VLANs properly configured and trunk links established.
Issue: After a brief power fluctuation, some trunk ports randomly stop tagging VLAN traffic correctly. Devices connected to access ports in those VLANs lose connectivity, but restarting the affected switch or reapplying the trunk configuration sometimes resolves the issue—though not always.
Troubleshooting Done:
- Verified trunk port configurations (switchport mode trunk with proper allowed VLANs)
- Checked spanning-tree status to rule out loop prevention issues
- Confirmed there’s no native VLAN mismatch
- Tried disabling and re-enabling the interfaces
- Observed that show vlan brief still lists the VLANs correctly
Question:
Has anyone encountered this rare issue where power fluctuations affect VLAN tagging on trunk ports? Could this be an IOS bug, a hardware issue, or something else? Any insights or troubleshooting steps would be greatly appreciated.
This type of question highlights a real but uncommon issue that can stump even experienced network engineers. Let me know if you'd like any refinements!
