For LOS (Loss of Signal) red lights on fiber or advanced gateways, it usually means the incoming optical line is not detected or has low signal. Double-check that the fiber line is connected properly and that there's no bend or physical damage. If issues persist, an on-site. A red light on your router can be a source of frustration and confusion. In this comprehensive guide, we will walk you. This guide will walk you through what the LOS light means, why it blinks red and step-by-step instructions on how to resolve the issue, including resetting your router. Sometimes it may be due to a problem with your internet service provider, although you could also be experiencing this issue due to improper configuration of your router, a poorly connected cable, etc. Then there is something wrong with the connection.