extending ASUS wifi network with Airport Extreme

No worries. You cannot have Double NAT unless the Router Mode on the AirPort is set to DHCP and NAT.

If you did have Double NAT, the AirPort would be blinking amber, and a Status message in AirPort Utility would indicate that you do have Double NAT.

On your Mac.....

Open AIrPort Utility

Click on the picture of the AirPort router

A smaller window will appear. Look for Wireless Clients to see the devices that are currently connected to the AirPort. You may have to figure out some puzzles though, if the device names do not appear. It is possible for the AirPort Utility to display the IP Address assigned to a device, the Hardware Address of the device, or the name of the device. No way to control what is displayed.

The Asus interface should have some similar way to identify devices that are connected to the Asus.

It doesn't make sense that both the ASUS and the AE could simultaneously be showing the Macbook as a wireless client, does it ?

You know for sure that they cannot both (ASUS and AE) have wireless connection at the same time.

The problem is simply time it takes to refresh the listings.

You will know which router you are connected to by the BSSID.

Hold the option key when you click the wireless fan. You will then see a more comprehensive listing. It will include BSSID. This is the MAC address of the wireless on the router you are connected to.

In my setup 14.xx.etc is the Asus.

The airport Time Capsule is 6c:xx etc.

There is a better way to control things.. to ensure you know which it is connected to. A wee bit complicated.. but I find it works better than AE in bridge. The info is in a post here.. if you want me to help with this setup I can do it specifically for your system.. if you give me some info about the Asus setup. I happen to run a similar Asus router so very familiar with the configuration.

No DNS error, Airport roaming network

Things are goofy when you try use hardware from two different manufacturers.

The thing that's no so confidence-building, though, is that the AE still shows the Macbook as a wireless client.

Things do not update quickly. It might take some time 15-30 minutes or more for things to display correctly.

It doesn't make sense that both the ASUS and the AE could simultaneously be showing the Macbook as a wireless client, does it ?

No, but given what I have just said, it is not surprising.

If both the Asus and AirPort are broadcasting a wireless network that uses the exact same name and password, then Macs will usually do a decent job of switching to pick up the best signal when they move from one area to another, although the display in AirPort Utility may not immediately show the change.

iPhones and iPads tend to want to hold onto the original router to which they connect, even if you move the device close to the "other" router. They may switch after a few minutes, or not switch at all.

If you temporarily turn off the WiFi on an iPhone / iPad when you move it from one area to another, then turn the WiFi back on at the new location, the device will usually....but not always.....pick up the signal from the closer router.

Users often ask how to make sure that a device connects to a given router. The only way to do that is assign a different wireless network name to each router. Then, you will have to manually "switch" networks when you move a device from one area to another

Power off the entire network.....all devices.....modem, routers, printers, accessories, mobile devices, etc.....in any order that you want

Wait a full minute

Power up the modem, and let it run a few minutes by itself

Then, power up the next device connected to the modem, and let it run a full minute

Keep powering up devices one at a time about a minute apart until the entire network is back up

Check the network

You will need to be patient with this. Depending on how many devices you have in your network, it might take 15 minutes or more to get the network back up and running correctly.

This complete network power cycle will get things back in the proper sequence. Your network got out of sequence during the power outage, because different devices came back up at different times.

But just now a severe thunderstorm rolled through, which always made my ATT DSL go way to **** (further to **** than its baseline 3Mbps)

Even a momentary blip can really mess things up. You would want to do a network power cycle anytime things are acting weird on the network.

How are you checking Internet connection speeds?

No DSL service that I know of will be able to do much more than 20-25 Mbps. Cable can do much better, as can fibre optic connections.

Message deleted.

There are some advantages to the method that LaPastenague suggests. I was trying to keep things as simple as possible.

A network power cycle will fix about half of all problems about half of the time, so it is a good basic troubleshooting step to perform whenever things start acting weird.