Fan Behavior of 10G Switches with SFP Detect Feature Enabled

Zyxel_Adam Posts: 359  Zyxel Employee
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Switch models:


XGS2220 Series

XS1930 Series

XMG1930 Series

Firmware version:



A user notices the fans of the switch are spinning at high speed, even when there is no significant traffic loading and the ambient temperature is normal. He would like to know:

  1. Querying if the observed behavior is normal.
  2. Abnormal fan speed even with low traffic loading.
  3. Concerns about the fan constantly running at high speeds.

Root Cause:

The high-speed fan behavior observed in the switch is a normal operation. This behavior is a result of the switch monitoring the temperature of the SFP (Small Form-Factor Pluggable) modules using SFP DDMI (Digital Diagnostic Monitoring Interface). When the temperature of an SFP module exceeds its specified upper limit, the switch increases the fan speed to cool down the module and prevent overheating. This action is taken to protect the SFP module's temperature, rather than the overall temperature of the switch itself.


To manually reduce the fan speed, one can disable and re-enable the SFP detect function. By clicking on the "SFP" label displayed next to the fan, you can toggle the SFP detect on or off once entering the Hardware Monitor page. It's important to note that if the environment's temperature causes the SFP temperature to decrease, the fan will not reach its maximum speed again.

However, it is not recommended to disable the SFP detect function unless necessary. Disabling it may lead to unexpected issues or the need for repair if an SFP module overheats.