A community to help people learn, install, set up or troubleshoot their home network equipment and solutions.
There aren't any restrictions on what downstream device you can use.
Could be an address conflict. Check the lan address range on your Asus router. If it's using 192.168.1.x then it's conflicting with the AT&T gateway. Change to .3.x or .99.x or something else from 2-254.
Set AT&T's router to bridge mode.
If you want the AC88U to actually "route" traffic, then set your AT&T router to "bridge mode". There's probably tons of instructions online as to how to accomplish that.
If you don't bridge the AT&T modem, you'll end up behind two layers of NAT, which can cause problems with gaming and port-forwarding.
IP Passthrough is the only way... Make sure to change your WAN IP on the Asus to your actual IP so you don't get a double NAT. I have had this setup for a long time and absolutely love it. no issues whatsoever. My PS5 and XBOX working with no issues at all.
Would you provide the model of your AT&T router? ISPs have a bad habit of claiming their devices cannot be placed in bridge or pass through mode, when that isn’t always accurate.
TheBadCable
It’s not a modem. It’s an ONT or ONT/Gateway.