Hi plaurits,
We see you're working on an Airport Extreme which looses the internet connection. Looking at your screenshot, we do see some issues.
No internet connection, Ethernet not connected
No DNS servers
1. You'll want to make sure that the cables are connected correctly:
Physically connect the base station to your modem
1. Connect the power cord to the Power port on your base station, then plug the power cord into a wall outlet.
2. Connect an Ethernet cable to the WAN port on your base station, then plug it into your DSL or cable modem.
3. Note: If you don’t use a modem, or connect in a different way, get connection instructions from your ISP.
Set up a new base station using AirPort Utility on Mac - Apple Support
2. When the cables have been reseated, you'll want to restart the fiber box modem and AirPort Extreme.
• If you're still seeing no internet/ethernet connection, verify no breaks or damage to the cables, or Ethernet ports.
• If the only issue which remains is no DNS servers, you'll want do a reset as shown below,
Reset 802.11b/g models of AirPort Extreme Base Station
Locate the reset button on the base station, next to the ports. When instructed to do so, press this button with a pen or straightened paperclip.
Soft reset
1. Make sure that the base station is connected to power.
2. Hold down the reset button for 10 seconds, then release the button.
Factory-default reset
1. Disconnect the base station from power.
2. While holding down the reset button, plug the base station into power and continue to hold the reset button for about 5 seconds, until you see the three status lights turn on. Then release the button.
How to reset your AirPort base station - Apple Support
Then, in AirPort Utility click on "Other Wi-Fi Devices" and then select device for setup.
Set up a new base station using AirPort Utility on Mac - Apple Support
If the issue happens again, you'll want to verify with the ISP if the fiber box needs a firmware update.
You can also test with a different internet network, to isolate if the issue is with the AirPort Extreme or the fiber internet.
Take care!