Why my airport extreme got green light but no internet connection?

If your Airport Extreme is not connecting to internet then you need to configure your device in the following way -

• First of all, power on Airport Extreme Base Station by plugging it into the wall. After plugging the device, open Airport Utility app.
• Next, move to the top left side of the screen and you will see Airport Utility dialog box. After this, tap on “Other WiFi devices” or “Other Airport Base Stations”. Now, click on Airport Extreme that is listed in the displaying list. If it is not listed then wait for a few moments so that it can come up.
• Move to Network name and then tap on option “Base Station Name”. Note one thing i.e., you have to enter venue name followed by TB.
• In next step, you have to enter a password that you could remember easily. Again enter the same password in the “Verify Password” field. After entering a password hit Next button.
• If your Airport Extreme is not connected to the modem then just click on Next button. Just choose the option, “Don’t send”. Again hit Next button.

• Now, go through router’s setup. When setup process gets complete, you will see a notification. The notification will appear in the bottom right-hand corner, just click on Done. After this, click on the picture of Airport Extreme base station that is present in Airport Utility. Now, Airport Utility will report three errors, just click on each error and ignore them.
• After ignoring an error, you will see a green light. Once you see three green lights, just click on Edit button.

• Move to the top side and click on Wireless > Wireless options.

• To allow a 5Ghz frequency band, just click on the box that is present on the top side. In the present time, 5Ghz is preferable as it provides faster WiFi. Then click on Save button.
• Next, click on Update.

• Once green light in your Airport Extreme router blinks, just understand that your device is good to go.

Reset the Airport Extreme back to default settings and start over. You will also have to release the WAN IP on the modem by power cycling it. If the router doesn't grab an IP from the modem after the power cycle and reset, the chip that controls WAN functionality in the router is most likely bad. There is a separate chip that controls the 3 LAN ports, and that's why they work okay when you plug into them. If this is not working then go to Apple menu and select System Preferences. Choose Built-in Ethernet from the Show pop-up menu and go to PPPoE tab. Click the PPPoE Options button. Deselect the "Connect automatically when needed" option. Finally, click OK and apply the changes.