Which factor commonly leads to link flapping on a fiber optic link?

• A. Excessive routing protocol convergence.
• B. Incorrect IP addressing on host.
• C. Over-lightened laser levels.
• D. Dirty or damaged fiber.

Answer: (D)

Link flapping on a fiber optic link happens when the physical signal path becomes unstable. Dirty or damaged fiber introduces intermittent attenuation or loss of signal, causing the receiver to briefly lose synchronization and the link to go down, then come back up once the signal improves. This up-down cycle repeats, which we recognize as flapping. The fiber path is the bottleneck here, so contaminants, nicks, or breaks directly create the instability.

In contrast, issues like routing protocol churn, incorrect IP addressing, or transmitter power anomalies at the endpoint don’t cause the link itself to repeatedly go up and down. They affect how traffic is routed or how devices interpret addresses, but not the physical connection state. For practical troubleshooting, inspect and clean connectors, look for visible damage, test with optical power meters or OTDR, and replace damaged fiber or connectors as needed.