When the opposite end is normally emitting light, the optical port displays online, and the optical port of the opposite switch displays down, which causes the entire frame to interrupt services. The optical port connected to the failed optical module can be. Plug a loopback cable or loop the optic -- Does the link light go on? 12-30-2022 01:22 AM Yes, with a loop is OK, or with the circuiti in UP state, we have UP port with the same RX power on the SFP+ module, if the carrier shutdown the circuit, we have DOWN on port but RX power still the same. At this. Before troubleshooting the issue, please look at our 16 tips for troubleshooting your optical transceiver connections.