I had an older arris modem and used it with my night hawk r7000 and it worked great. I got about 100mbps over wifi. The built in wifi did not work well for the size of my house so I used my night hawk. The modem started having problems so xfinity gave me a new modem. Again the modems wifi did not work well, so I used my night hawk and again it worked, but the speed was much slower (20mbps). I spoke to xfinity and they said in order for my router to work to it potential I needed to enable the wifi bridge mode to turn off the modem wifi and enable the potential of my wifi. It made sense so I went into the admin settings and enabled the bridge mode. This actually stopped all my wifi routers from connecting. I even tried using my google hub and same thing. When I disabled the bridge I was able to use it again. I think there is some confusion with xfinity. Any idea what is going on and why bridge mode disables my wifi routers from connecting to the internet?
Is this what you are referring to?
I think what may be happening is you need to be sure the cable from your modem is plugged into the Wan port on your router. When you enable bridge mode it makes the comcast piece JUST a modem. If you hardwire something to the router when bridge mode is enabled is it on the intenet? That would tell you if you are setup correctly. Bridge mode would have nothing to do with the wifi on your nighthawk as is it a totally seperate device.