My computer works when connecting directly to the Spectrum modem. I connect my GL-iNet router and go through the setup process and it claims there's no Internet. I saw someone mentioned cloning the Mac address. I tried that and still nothing. I've been on the phone with Spectrum but they don't help much because I don't think they really know more than "have you tried to reboot the router and modem?" I'm really frustrated because I've never had issues with the last three routers I've had. They were just plug and play.
Modem -
Make: Hitron Technologies
Model: EN2251
Router -
Make: GL-iNet
Model: GL-MT6000
HELP!! 
Hi,
-
Please make sure that the upper network is connected to the WAN port of MT6000. And check the INTERNET page of MT6000 to see if the IP address is obtained.
-
Verify router settings
Log in to the router's admin page (Default IP address: 192.168.8.1).
Check the network settings, including the IP address, subnet mask, gateway, and DNS settings. If you are using DHCP, please make sure it is enabled and working correctly. If you are using a static IP, double-check the entered values.
- Check the hardware
Inspect the Ethernet cables for any visible damage. Try replacing the cable with a new one.
Check the router's ports. If possible, try using a different port on the router.