No internet connection when fiber optic cable is connected to router

A no internet connection issue with a fiber optic cable often stems from physical cable problems, router configuration errors, or ISP-related restrictions.Check Physical ConnectionsEnsure the fiber optic cable is securely plugged into the correct port on your router or ONT (Optical Network Terminal). Inspect the cable for visible damage, sharp bends, or loose connectors, and clean the connectors with a lint-free wipe and isopropyl alcohol if necessary . If your router uses a transceiver, check for a “LOS” (Loss of Signal) LED, which indicates a connectivity problem .Verify Router and Device StatusRestart your devices: Power off the ONT, modem, and router, wait 30 seconds, then power them back on to reset temporary glitches .Check LEDs: The Power, PON, and Data LEDs on the ONT should be on. On the router, the WAN or Internet LED should indicate a valid connection .Test with a wired device: Connect a computer directly to the router via Ethernet to rule out Wi-Fi issues .Check IP Address and ConfigurationLog into your router's management page and check the WAN/Internet IP address. If it shows 0.0.0.0, the router is not receiving a valid IP from the ISP, which could be due to a modem/router misconfiguration or MAC address restriction . Possible fixes include:Restarting the modem and router in the correct orderCloning your computer's MAC address to the routerChanging the router's LAN IP range if it conflicts with the modem Firmware and Software UpdatesEnsure your router and ONT are running the latest firmware to avoid compatibility issues . Older routers may require updates or replacement if they cannot handle the fiber connection properly .ISP and Service ChecksConfirm there is no outage in your area by checking your ISP's service status page or app .Some ISPs lock internet access to a specific device; contacting your ISP may be necessary if the router is not recognized .Advanced TroubleshootingIf the above steps fail:Use a fiber power meter or OTDR to check for signal loss or breaks in the fiber line .Swap transceivers or test with a known-good router to isolate hardware issues .Monitor network traffic with tools like Wireshark or PRTG to detect configuration or routing problems . By systematically checking physical connections, device status, router configuration, and ISP restrictions, most fiber internet connectivity issues can be resolved without professional intervention.