bridge mode setup?

Your AirPort router should already be configured to operate in "Off (Bridge Mode)".....if it is set up correctly.

Verify this as follows on your Mac:

Open Finder > Applications > Utilities > AirPort Utility

Click on the AirPort router

Click Edit in the smaller window that appears

Click the Network tab at the top of the window

The setting for Router Mode should read "Off (Bridge Mode)". If it doesn't, then change the setting as needed and click Update to save the new setting.

If the Uverse router continues to be confused about what IP addresses it has issued to what product, you will need to check with ATT support for assistance.

Before you call ATT, try the following if you have not already done so.

Perform a complete power cycle on the entire network as follows:

Power off every device on the network....computers , printers, mobile devices, etc.....in any order that you want

Wait a minute

Start the Uverse modem/router and let it run 2-3 minutes

Start the next device that is connected to the Uverse and let it run a full minute

Keep starting devices one at a time the same way about a minute apart until the entire network is powered back up

Keep an eye on the network

A power cycle like this gives the Uverse modem/router a fresh start and an opportunity to get everything organized again on the network that it is controlling.

If things work OK for a month or two and then you start to see the duplicate IP address messages, that would be time to perform a complete network power cycle again.