Check the optical power of the switch interface

You can check optical power on a switch by using CLI commands to view TX (transmit) and RX (receive) levels, typically via show interfaces transceiver detail on Cisco switches.

Understanding Optical Power

Optical power measures the strength of light signals in fiber connections. Two key metrics are: TX Power (Transmit): Light leaving the switch's SFP module.

Weak T

X may indicate a failing laser.

R

X Power (Receive): Light arriving from the remote device.

Low R

X is a common cause of intermittent link issues. Values are measured in dBm, where more negative numbers indicate weaker signals (e.g., -20 dBm is weaker than -5 dBm) and should be compared against the SFP's specified thresholds to detect problems. Checking Optical Power on Cisco SwitchesVerify SFP Recognition: Ensure the SFP module supports Digital Optical Monitoring (DOM) and is recognized by the switch: CodeCopyshow inventory View Interface Status: Identify the interface type and number: CodeCopyshow interface status Check Optical Power: For Catalyst switches: CodeCopyshow interfaces transceiver detail For SMB or other Cisco platforms: CodeCopyshow fiber-ports optical-transceiver For a specific interface: CodeCopyshow interfaces transceiver detail Interpret TX/RX Values: Compare the TX and RX dBm values against the SFP's low and high warning thresholds.

Deviations indicate potential signal degradation, misalignment, or failing hardware.

Additional Tips

If the SFP does not support DOM, optical power cannot be read. Regular monitoring helps prevent intermittent flapping, packet loss, or err-disabled states. Some platforms allow filtering output for easier reading, e.g., | include dB on IOS-XR or NX-OS.

Always check both ends of the fiber link to ensure proper signal levels. By following these steps, you can effectively monitor and troubleshoot optical power on your switch, ensuring stable fiber connections and early detection of potential issues.