AT&T home gateway devices don’t have a true bridge mode that you can use if you want to use your own router with their service. But there is an acceptable substitute. So here’s the closest thing you’ll find to AT&T U-verse bridge mode and how to enable it. This also works with AT&T Fiber and everything else AT&T calls AT&T Internet.
What bridge mode is
Bridge mode effectively just connects two computer networks. The idea is to turn the AT&T device into just a dumb modem and bypass all of its other functionality.
Using DMZ Plus as a substitute for AT&T U-verse bridge mode
The gateway that AT&T provides doesn’t have a bridge mode, but it has another feature that’s an effective substitute.
But first, we have to take care of its networking.
To make this easier, disconnect everything from your AT&T gateway except for one computer (it can be a laptop, but ideally connected via a wired connection), and the router you want to bridge to.
AT&T gateways default to a 192.168.1.0/24 network and an address of 192.168.1.254. If your router doesn’t live on 192.168.1, you’re golden. But it seems like at least 50% of consumer routers also live on that network. If yours does, you’ll have to reconfigure the AT&T router so you don’t get a conflict.
Log in to the AT&T gateway. The password is on the underside of your router. It’s probably just a long number. Navigate to Settings > LAN > DHCP. Change the range to 172.16.0.0. Then scroll down to the end and click Save.
You’ll lose your connection at this point. This is a pretty good time to plug in your third-party router. Then either unplug your laptop’s network cable and plug it back in, or renew your DHCP lease with the command sequence ipconfig /release followed by ipconfig /renew . Now you’re ready to reconnect. Point your browser at 172.16.0.1 and log back in.
Enabling DMZ Plus mode
Navigate to Settings > Firewall. Click Applications, pinholes and DMZ. You should see two devices on the screen: your laptop and your third-party router. Click on the router, then click Allow all applications (DMZ plus mode).
Now plug your laptop into your third-party router and visit its configuration page, probably at 192.168.1.1 if it’s like most routers. Find its network status page and check its IP address. You should see your public IP address, the same address you see if you visit ipchicken.com. If you see a 172.16 address instead, revisit your settings on the AT&T router and make sure you didn’t forget to click apply somewhere.
I assume if you want to use the AT&T gateway as a bridge, you also don’t want its wifi. Plug your laptop back into the AT&T gateway and connect to 172.16.0.1. Click on Settings > LAN > Wi-Fi and then scroll down to Wi-Fi Interface. Select Disabled. If your gateway has both 2.4 GHz and 5 GHz radios, which newer ones do, scroll down to the section labeled 5 GHz Wi-Fi Radio and do the same thing there.
How this differs from a true bridge
This differs from a true bridge mode in that the remaining ports on your AT&T gateway still function and still hand out network addresses. This allows you to get into the device if you ever need to administer it, so it’s not an altogether bad thing. But if you don’t want people bypassing your other router, you’ll need to protect physical access to the AT&T device.
That’s how you enable the closest thing that exists to AT&T U-verse bridge mode.