No internet. Router front lights are off, back back Ethernet port lights are on.

Have you first tried power-cycling / re-starting the device by unplugging it for a minute ? Still no joy ? Try hard resetting the device to factory defaults by pressing and holding in the recessed reset button on the rear (or use the WPS button if it doesn't have a reset button hole) for 25-30 seconds. This can sometimes clear up some weird behavior issues. You will lose any customized settings, and they will need to be re-configured from scratch if you do the latter. If it's still not working, it's probably toast. Try getting it swapped for a new one. Good luck !

Hey @user_0rlyox. Thank you for visiting our official Xfinity Forums Community support page. We would be more than happy to assist in troubleshooting the Xfinity Internet service. Do you happen to know what model modem you are using to access the Internet? You can visit our 'Overview of Xfinity WiFi Gateways and Routers' support page to see our most frequent models in use. Are you an Xfinity Internet subscriber or NOW Internet subscriber? We hope to hear from you soon.