extended Airport wireless network and ATT Arris NVG589

Anytime that you change Internet Service Providers, or you change the modem on the network.......you really need to reset each of the Apple AirPort routers back to default settings and then set it up again. This gives each AirPort a clean slate, rather than have it retain settings from the "old" modem.

If you want to try a shortcut.....that may or may not work.....for the extender that is connecting using wireless.....

Perform a Factory Default Reset on the AirPort Express as follows:

Power off the AirPort Express

Wait a minute

Hold in the reset button on the back of the device first.....and keep holding it in for an additional 7-8 seconds while you simultaneously plug the power back into the AirPort Express

Release the reset button on the Express and give it a full minute to restart to a slow, blinking amber light status

Now power off the Express again and move it to the same room or close proximity to the AirPort Extreme

Power off the AirPort Extreme, wait a few seconds, then power it back up again and let it run for a full minute

Now power up the AirPort Express and set it up again to "extend a wireless network"

If you get a green light on the Express after it restarts, power it off and move it to a location that is approximately half way between the AirPort Extreme and the general area where you need more wireless coverage. Then, power up the AirPort Express again and check to see if things are working correctly.

Perhaps a simpler start: am I correct in starting with the Extreme base station in DHCP/NAT mode when connected by ethernet cable to the Arris in bridge mode?

Unless something has changed very recently with the Arris modem/router that ATT provides, "bridge mode" is not really an option on that device.

If you find that you do have that option, then you could setup the AirPort Extreme to use DHCP and NAT correctly, without the Double NAT indication.

If you call Apple Support, they will advise you to run the AirPort Extreme in DHCP and NAT mode....even if the Arris is also providing routing services. This will produce a Double NAT indication of course.....as you see now when you try this......but Apple will tell you to use the option to "ignore" the Double NAT, so the AirPort will display a green light, instead of blinking amber.

Whether or not Double NAT is a serious "error" is a matter of opinion. It can certainly cause problems on some networks, but these issues are not possible to predict in advance. You have to try it out and see.

Might be worth a try if you are continuing to have difficulty with the AirPort Express when the AirPort Extreme is setup in Bridge Mode.

I doubt that ATT offers a simple model option any longer, which would be simplest fix of all.

there is a complicated way to turn wireless off

That might be.....but turning off the wireless does not turn off the routing functions of the ATT modem/router......so it is still acting as a router providing DHCP and NAT services for the network.

What you want is an option to turn off both DHCP and NAT on the ATT modem/router......which would allow it to function as a simple bridge mode modem. I cannot say whether the device has this type of capability.

Then, the AirPort Extreme can provide the DHCP and NAT routing functions for the entire network and there is no Double NAT that way.

I will try ignoring the doubt NAT and see how it goes

If you don't want to watch a constant slow blinking amber light on the AirPort Extreme......

Open AirPort Utility

Click on the image of the AirPort Extreme

Look for a setting for Status in the smaller window that appears

Click on the small amber dot next to Status

Use the option to "ignore" the Double NAT, so the AirPort Extreme will display a green light

Double NAT can create some possible issues on any network.....among some of the common things are.....

Slower browsing

Some web sites may load while some may not

Online interactive game consoles will not work correctly

Port forwarding will not work correctly

Sometimes you can get away with Double NAT on a simple home network.....and sometimes you can't. Let us know how it works for you, if you can.