AT&T Fiber Router to NetGear Nighthawk XR450

I have an XR450 Gaming Router, I just added a fiber line from AT&T into my house which is also on a router, for some reason when I try to run the AT&T Router through my Netgear router, I get a no DNS error message and nothing works.  I work fine on the AT&T router alone, which is how I am typing this message.  My Netgear router works fine on my cable modem.  How do I put the two togther to work so that I can run Fiber speed and have the router wifi push it to other areas of my network.  Any help would be great, I was told to buy google wifi extenders and be done with Netgear, but I don't see why this would be able to work and I can't find a setting I probably have incorrect.