Questions: Link Flaps - Bad Optic

• What do the ethtool diagnostics show for the SFP+ module (optical power, temperature, voltage)?
• Is the cable/optic a genuine Cisco-compatible module, or a third-party that might be rejected?
• What does the switch-side port log show (error counters, CRC errors, link flap count)?
• Is the cable properly seated in both the server NIC and the switch port?
• Could this be a NIC firmware or driver issue rather than a cable/optic problem?
• Are there environmental factors (temperature in the rack, cable bend radius exceeded)?
• Does swapping the cable to a different switch port change the behavior?
• What is the negotiated speed and duplex, and does it match expectations?
• Are there FCS/CRC errors incrementing on either side?
• Has the NIC firmware been updated recently?