Log in to the switch console to run the privileged EXEC mode of the Cisco switch, use the fiber-ports-optical-transceiver command. The Output Power (mWatt) field in the command output indicates the received power of the optical module, and the Input Power (mWatt) field indicates the. Monitoring the optical power of SFP (Small Form-factor Pluggable) modules is a critical step in maintaining stable network links. Even if an interface appears up, degraded Tx/Rx levels can cause intermittent flapping, packet loss, or err-disabled states. Checking optical power helps pinpoint issues. This article provides instructions on how to view the Optical Module Status on your switch through the Command Line Interface (CLI). The Cisco Small Business Series Switches allow you to plug in a Small Form-factor Pluggable (SFP) transceiver in their optical modules to connect fiber optic cables. When optical modules operate on a switch, it is usually necessary to read the module's internal information to understand its working status—such as connection status and real-time metrics like optical power and temperature. Additionally, identifying module information helps detect coding. Have you ever encountered a Cisco switch interface that constantly flaps (goes up and down) or suddenly enters an err-disabled state? Before you blame the switch or replace the cable, you need to look at the invisible data: the light levels. This guide provides complete, step-by-step CLI commands to view module type, DOM/DDM diagnostic data, vendor details, and compatibility information, fully. Some switches like Cisco, Hpe, Brocade will offer CLI (Command-Line Interface) reference for users to view SFP modules DDM/DOM information, which includes transceiver temperature, the supply voltage in the transceiver, laser bias current, RX power TX power (mW or µW or dBm).