This guide gives a practical, CLI-focused workflow for checking SFP health and diagnostics on Cisco switches, shows the exact commands you'll use, explains what the numbers mean, and compares OEM (Cisco) vs third-party modules so you can pick the right SFP module . This guide gives a practical, CLI-focused workflow for checking SFP health and diagnostics on Cisco switches, shows the exact commands you'll use, explains what the numbers mean, and compares OEM (Cisco) vs third-party modules so you can pick the right SFP module . 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. In the switch command line, enter bcmsh. Take the lane number obtained from the first step and divide it by 2 (no need to divide by 2 for N9500-128QC devices). This corresponds to the "physical" number in show portmap, such as 157. Many enterprise switches from vendors like Cisco and Juniper Networks provide built-in commands that allow engineers to read Digital Optical Monitoring (DOM or DDM) information such as temperature, voltage, transmit power, and receive power.