Connecting ORBI RBR50 to Uverse Arris BGW210-700

I have read the instructions but I do not understand why I need to put the ATT Modem in IP Passthrough mode.  When I connected my 3rd party router (EERO) via ethernet to back of ATT Modem it transmits a wife signal and I obtain full download speed.  Now the ATT WiFI is still active but I do not connect to that.  it just shows on my available wifi networks, similar to how I see my neighbors wifi network.  I am not sure why I need to go through all of these settings unless there is some advantage.  

You're not trying to use the Eero and Orbi at the same time are you? They are both mesh systems and cannot be used together -  you'll need to use one or the other.

Nevermind: I see the posts were from different people.

I am only using the EERO. I was searching the community and found a reference to Orbi which I tagged onto as it said you had to make changes on the ATT Modem. However, I hooked up the EERO without making changes to the ATT Modem. So I was wondering why changes had to be made to the ATT Modem (I do not understand how it conflicts) if the 3rd party router was working fine.

Basically the ATT gateway is a router and so is the Eero. That means you are running two routers. It's often better to put the gateway in pass-through mode so your eero acts as your router. If you're not having any problems, I would keep doing what you are already doing.

This causes packet drops and other general issues that make it clear setting the Arris BGW210-700 in that pass-through mode is complete trash.

See my post below

I had the same issue, so I wanted to post my solution. One caveat, I am only using AT&T for internet, NOT UVERSE TV or phone.

I am somewhat tech-savvy, but NOT an IT expert, so here's what worked for me. My Orbi system (RBR50 with one satellite) was previously working with another internet provider.

Once AT&T BGW210 was installed and working, I connected my Orbi to it via an ethernet cable, and then also connected my Laptop via ethernet cable, and went to the device dashboard at http://192.168.1.254

Click on Firewall, then IP Passthrough, enter your device access code on the side of your BGW210 device.

Set Allocation Mode to Passthrough.

Set Passthrough Mode to DHCPS-fixed.

On Passthrough Fixed MAC Address, click on the drop down menu and select the RBR50.

Save changes.

Click on Home Network at the top, and then Wifi, and then Advanced Options.

Under 2.4 GHz Wi-Fi Radio Configuration turn Wi-Fi operation to Off. Do the same for 5 GHz Wi-Fi Radio. Save, and continue.

I powered off the Orbi RBR50, left it off, then restarted the RBR50 (power off, wait, power on). Once it came up (solid Broadband light), I powered on the Orbi.

Give it a good deal of time to connect, maybe even 20 minutes. For me, micromanaging the Orbi caused me some unneeded headaches.

Once my Orbi Wifi was working, I checked it with the Orbi app, but even though I had wifi, and could complete successful speed tests, the app showed Internet: Offline.

I then connected my Laptop to the Orbi via ethernet cable, and logged onto the Orbi dashboard at http://orbilogin.com

You'll need your username admin and password from previous Orbi setup.

Upon login, it told me there was an IP address conflict between the modem and the router.

It automatically changed its IP address to a different range to resolve the conflict, and took me to the device dashboard.

Now the Orbi app shows Internet: Online.

Everything is working great so far. I hope this helps someone else in the same boat!