Router behind a router questions:

I know that this has been asked a hundred times and my guess is because everyone seems to have problems with this. I'm almost convinced at this point that AT&T purposely breaks this to discourage the practice. However, I've been known to be wrong a time or two.

I've successfully done this setup with two other ISPs with no issues whatsoever ( - one of those being the notoriously difficult Dumbcast). With AT&T's Pace 5268AC, I've tried the router in DMZ setting, the cascaded router setting, and the cascaded router-without-officially-setting-it-in-the-router-setting. None of these have produced satisfactory results. I have Gig speed Fiber but using the previous methods the best speed I get is 45 Mbps down 120 Mbps up. Equipment-wise, everything that I use, I've used before: all 1000 Mbps NICs, Cat5e or Cat6 cable, Gigabit routers with Gigabit ports, Gigabit switches, etc.

It's possible that settings that I've used in the past just won't work with AT&T, so I'm interested in hearing from those that have gotten satisfactory results. What exactly are you doing? Please expound...

(And for those questioning why one would need to cascade their own router, the Pace, and I've had three, is horrific in performance. I have a home with a big, open floorplan and the Pace can't deliver 20 feet away in a straight line wirelessly. All of my routers, from the very expensive to the very cheap, almost cover the entire 3500 sq ft. I wish for the old days when you didn't have to have the ISP gateway at all. Even Dumbcast gives you a pretty good quality gateway although it's neutered.)