If your internet is not accessible after connecting a fiber optic cable to a switch, the issue is likely due to configuration errors, PPPoE authentication, or IP conflicts rather than a physical connection problem.

Check Physical Connections

Ensure that the fiber optic cable is properly connected to the ONT (Optical Network Terminal) and the switch. Look for any visible damage, sharp bends, or loose connectors. If possible, clean the connectors with lint-free wipes and isopropyl alcohol to remove dust or oil, as contamination can block the signal . Verify that the switch and any transceivers are powered on and that indicator LEDs show normal operation.

Verify Router and WAN Settings

If you are using a router behind the fiber connection, check the WAN connection type. Many fiber ISPs require PPPoE authentication with a username and password. If your router is set to automatic IP or DHCP, it may not receive a valid public IP, resulting in a "connected but no internet" status . Log in to your router's management page and confirm:

• WAN/Internet port is connected to the ONT or fiber modem.
• PPPoE credentials are correctly entered if required.
• The router is not conflicting with the fiber gateway's IP (bridge mode may be necessary) .

Check for IP Conflicts

Fiber gateways often assign IP addresses that can conflict with your existing network. If your router or switch is using the same subnet as the fiber gateway, devices may fail to access the internet. Consider:

• Setting your router to a different LAN subnet (e.g., 192.168.2.x if the gateway uses 192.168.1.x).
• Using bridge mode on the fiber gateway to allow your router to handle routing .

Restart Devices in Correct Order

Power cycle the network devices in the following order:

1. Turn off the fiber ONT/modem.
2. Turn off the router and switch.
3. Wait 1–2 minutes, then power on the ONT/modem.
4. Power on the router.
5. Finally, power on the switch and connected devices .

Test Direct Connection

To isolate the problem, connect a computer directly to the fiber modem or ONT and attempt a PPPoE login if required. If the computer can access the internet, the issue is likely with the switch or router configuration. If it still cannot connect, the problem may be with the ISP or the fiber modem itself .

Additional Considerations

• Ensure your router firmware is up to date to avoid compatibility issues .
• If using a managed switch, check for VLAN or port configuration that may block internet traffic.
• Contact your ISP to confirm that your fiber service is active and that your MAC address is registered if required. Following these steps should help identify whether the problem is physical, configuration-related, or ISP-dependent, and guide you toward restoring internet access.