How to check the optical power of a switch port

You can check the optical power of SFP ports on a switch using CLI commands to view TX (transmit) and RX (receive) power, typically via Digital Optical Monitoring (DOM) or DDM.Step 1: Verify SFP Recognition

Before checking optical power, ensure the SFP module is recognized by the switch:

• Run show inventory to confirm the SFP is detected, including part number, serial number, and vendor information .
• Check link status with show interfaces status to ensure the port is up and the correct media type is used .

Step 2: Check Optical Power

For Cisco switches, the commands vary by platform: Catalyst / Enterprise Switches:

• Use show interfaces transceiver detail or show interface transceiver detail to display TX and RX power in dBm, along with temperature, voltage, and bias current .
• Example output includes:
  • TX Power: Light leaving the switch (indicates laser health)
  • RX Power: Light received from the remote device (common cause of link issues if low) Small Business Switches:
• Use show fiber-ports optical-transceiver to view optical module status, including transmitted and received power, temperature, voltage, and loss-of-signal (LOS) indicators . Other Platforms (IOS-XR, NX-OS):
• Commands like show hw-module subslot transceiver status or filtering with | include dB can display TX/RX power for troubleshooting .

Step 3: Interpret the Values

• Compare TX and RX readings against the SFP's Low Warn and High Warn thresholds. Deviations may indicate:
  • Misaligned fiber
  • Dirty connectors
  • Failing SFP module
• Typical TX/RX ranges depend on the SFP type (e.g., 1G, 10G) and fiber distance .

Step 4: Additional Checks

• If the port is err-disabled due to unsupported transceivers, use no errdisable detect cause gbic-invalid (with caution) to allow third-party modules .
• For detailed SFP info, including EEPROM data, run show idprom interface or show idprom transceiver extended . By following these steps, you can monitor optical power, detect signal degradation early, and troubleshoot fiber link issues without unnecessary hardware replacement.