Orbi mesh router (RBR50) with an ATT Gateway (BGW320-500)

I believe that you need to place your gateway in pass through mode (similar to bridge mode) if you want to connect another router to it. That way you avoid a double NAT and leave all of the heavy lifting to the Orbi. I use the RBR50 (not with AT&T) and it works very well for the size of our house and property. As a side note, if you can hard wire the satellites (at least one) for the back channel you'll get much better performance (reliability).

But i am told you also need to put the Orbi in AP mode, loosing the router functionality.

I had not heard that so hopefully someone else can elaborate. Placing the gateway in pass through mode should disable the router portion so that you can add a fully functional router to the gateway. If you can't, then you'd probably be better off to use the AirTies extender that AT&T sells. Using the Orbi as just an AP and not a mesh WiFi is a waste.

Thanks. This does make sense to me.

One last question.. should I turn DHCP server off on the BGW320-500 and let the Orbi manage DHCP?

You should not be able to turn of the DHCP server on the BGW320.   With the Orbi acting as a router, it will service any DHCP requests it sees and they'll never get to the BGW320.  The obvious exception would be things connected directly to the BGW320, but that's not going to be much, if anything.

I would change the LAN IP space on one of the two devices so that they both won't be using 192.168.1.0/24. Doesn't matter which you change.  192.168.2.0/24 or 172.16.1.0/24 (or any other private IPv4 address space is fine).  When you do this, then you can connect to the Gateway from the Orbi's network.  Otherwise, you won't be able to.  (Because if the Gateway is at 192.168.1.254 and the Orbi thinks it owns 192.168.1.0/24, it will not know how which 192.168.1.254 you mean).

Can you please expand on that last paragraph for a layman's understanding? How would I change the LAN space on the Gateway or the Orbi.

Oh, sorry.  On the Gateway, it would look like this:

I've changed the gateway's LAN address from 192.168.1.254 to 192.168.2.254, and altered the range of address it gives out via DHCP to Start: 192.168.2.64 and End: 192.168.2.253.  Don't forget to hit Save.

The same sort of thing could be done on the Orbi instead.  Can't show you a screenshot.  But you don't have to do both, either one is fine.

Once you make this change, remember that the local address of that device has changed, and you need to use the new IP to connect to it using the Browser.

Thanks! And, what if I don't do that?