I am planning to extend my network via "roaming" option using an Ethernet cable as the second router is not within range of the primary router. My question is can I use an airport express as the additional router ? My pirimary router is an extreme.

Under the roaming option mentioned in the KB do both routers have to be the same ?

No

Or can one be an express and the other an extreme ?

Yes

Bob

I've tried this set up but have had trouble configuring the Express. The support article offers choices I do not see when I configure in Airport Utility or via System Prefs > Network. I have gotten it to work by configuring the Express by connecting it directly to my mac with a ethernet cable... Not across the network or wirelessly.

I've been through this a couple of times and remain baffled.

The support article offers choices I do not see when I configure in Airport Utility

The support artilce is more than two years old, and would not be applicable if you are using a newer operating system like Lion or Mountain Lion on your Mac.

Might that be the case?

We need more information to be able to help:

Operating system you are using on your Mac?

Are you trying to use the AirPort Express to extend your other AirPort router wirelessly?......or......Will there be a permanent wired Ethernet connection between the two AirPorts?

Running OSX 10.8.4 and Airport 7.6.3

My goal was to permanently wire the Express to the Extreme (router). The wifi signal between the two seemed weak and wifi poor. Trying to create what I believe is termed a roaming network. Expect that will be faster and more stable.

Asides

- I had this setup before and have moved; and can't recreate it. I was tough the first time. Seems the Express tries to set up its own network and connection to the cable modem - despite my formatting to "extend existing network" or "join existing network."

- Another aside: Since trying and failing to establish a stable roaming network I've reverted to wifi, and it is working much better.

Setup of the AirPort Express is going to be much easier than you might imagine, although we'll go step by step here.

First, power on the AirPort Express for a few minutes, then hold in the reset button on the Express for 9-10 seconds and release. Allow a full minute for the Express to restart to a slow blinking amber light.

Connect the Ethernet cable from one of the LAN <-> ports on the AirPort Extreme to the WAN "O" port on the AirPort Express. I assume that you have previously tested the Ethernet cable to make sure that it is working correctly.

On your Mac, click on the AirPort icon at the top of the screen and wait a few seconds for a listing of New AirPort Base Station. Just below that, click directly on AirPort Express.

AirPort Setup will open up automatically, take a minute to analyze the network, then announce that the Express will be configured to extend the AirPort Extreme network.

Enter a device name that you want to use for the Express and click Next

Now AirPort Utility will confirm that the Express is being configured to extend using Ethernet.

When you see the message of Setup Complete, click Done

That's it. It might surprise you though, to learn that the Express has actually been configured to "create" a wireless network in this type of setup.