Fiber “No Link” Troubleshooting Checklist

When a link is down, resist random part-swapping. Work the physical layer in a fixed order and document each result.

1. Verify both ends. Source, destination, and port IDs must match the ticket/run sheet.
2. Inspect and clean. Check connectors for dust or damage, clean with the approved method, reseat until it clicks.
3. Swap the patch cable. Use a known-good cable of the same type and length class.
4. Swap the optic. Known-good, compatible optic — only if you are authorized.
5. Test the port. Known-good device or loopback test if authorized.
6. Check polarity. On duplex fiber, confirm Tx goes to Rx on both sides.
7. Look for physical damage. Crushed cable, tight bends, pinched doors, damaged panel ports.
8. Escalate with facts. List what you tested, what you ruled out, and what you need next. Stop swapping blindly.

The mistake that wastes the most time

Changing three things at once. If the link comes up, you have learned nothing; if it stays down, you have added three new suspects. One variable at a time, written down as you go.

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