You plug in the fiber optic cable, but the interface stays down. What’s wrong? Here’s a easy way to troubleshoot fiber optic connections on your switches and routers.
The first thing you should check is whether the two fiber optic cables are connected correctly. The transmitting side needs to match the receiving side on the other end. The thing is, our eyes can’t see the laser. And you really shouldn’t try to look into the fiber optic cable anyway. The laser can damage your eye.
If your SFP are emitting short wavelength laser (around 850nm), you can use the camera on your cellphone to see the infrared light. Use your cellphone to check that the emitting laser on the SFP goes to the receiving end on the fiber optic cable. If it’s not the case, you may need to cross over the cables.