How can I add my own router and firewall?

AT&T gateways don't support a true bridge mode, instead relying on IP Passthrough or DMZ. You can see a discussion of this In this thread.

Hey @Coliv00,

We are here to help with your inquiry. If you decide to use a third-party router there a two things you will need to do.

1. Research router compatibility to find the right fit.
2. Look into IP Passthrough and DMZ+.
   • There are two different types modes. Depending on the AT&T router. You will need to select the appropriate mode to setup your third-party router.

Let us know if this helps.

Max, AT&T Community Specialist

Thanks. I plan to use the Unifi USG Pro to replace my current router. Any additional information would be appreciated.

Correction, it's the Unifi Dream Machine Pro I'll be using.

Just curious if you ever got this to work?

Works fine but I would request new information on the process. Just to see if there are any updates to the process. There may be new equipment to consider.