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Check the temperature of the fiber optic router

Fiber optic router and SFP module temperatures can be monitored using Digital Optical Monitoring (DOM/DDM) commands on Cisco and Juniper devices to ensure safe operation and prevent overheating.Cisco Devices

On Cisco routers and switches, SFP modules support Digital Diagnostic Monitoring (DDM), which reports real-time parameters including temperature, voltage, and optical power. To check temperature:

  1. SSH or console into the device.
  2. Use the following commands:
    • show inventory — lists installed SFPs with Product ID, Version ID, and serial number.
    • show interface transceiver detail — displays DDM metrics including temperature (°C), voltage, Tx/Rx power, and bias current.
    • show interfaces status — confirms port connectivity.
    • show logging | include transceiver — checks for errors or unsupported transceivers.
  3. Interpret readings: DDM outputs include thresholds for high/low alarms and warnings. If the temperature exceeds the high alarm threshold, the module may need replacement or cooling adjustments. Abnormal readings may indicate dirty fibers, damaged optics, or environmental issues (Cisco) .
Juniper Devices

Juniper switches provide Digital Optical Monitoring (DOM) for SFP, SFP+, XFP, QSFP+, and CFP modules. To check temperature:

  1. Access the CLI on the device.
  2. Run show interfaces diagnostics optics to display:
    • Transceiver temperature in Celsius and Fahrenheit.
    • Laser output power, received optical power, voltage, and TEC current.
    • High/low alarm and warning flags for temperature and other parameters.
  3. Interpret alarms: High or low alarms indicate the module is outside normal operating limits and may require immediate attention, while warnings suggest conditions approaching thresholds .
Best Practices
  • Monitor regularly: Periodic checks help prevent unexpected link failures and extend module lifespan.
  • Trend temperature over time: Use DDM/DOM readings to identify gradual increases that may indicate cooling issues.
  • Check environmental conditions: Ensure proper airflow and ambient temperature in the router or switch environment.
  • Respond to alarms: Replace or reseat modules if temperatures exceed safe thresholds or if repeated warnings occur. By using these commands and monitoring practices, network engineers can maintain optimal fiber optic router performance and prevent thermal-related failures.
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Technical note

This reference is intended for preliminary specialty-cable research. Compatibility, link budgets, fire performance, installation methods, test limits and applicable standards must be verified for the specific project.

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