Several reasons can cause the LOS light to blink red: Fiber Optic Cable Damage: A physical cut or bend in the fiber optic cable can disrupt the signal. The LOS light on your router indicates the status of your internet connection to the Internet Service Provider (ISP). When it's green and steady, everything is fine. However, when it blinks red or stays solid red, it signifies a Loss of Signal, a problem preventing your router from communicating. The tables in this article provide detailed information about the possible appearances of the LED lights on each device, the possible causes of each state, and what you should do.