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Interpreting SFP RX power: -40 dBm or below means no light; use an OTDR or light meter to test the fibre
The poster asked how to test fibre cables from a switch. The guidance covers reading optical levels with show interfaces transceiver / show controllers, comparing TX and RX at both ends, and recognising that a reading of -40, -50 or -80 dBm means no signal is being received. Hardware involved…