Q: How to extend my network

Any of the Apple base stations.

1. Airport Extreme

2. Airport Express

3. Time Capsule

The Airport Express will be the cheapest soluiton unless you need something more.

See this Apple article. In the illustration, you can substitute any Apple base station for the extended one on the right.

http://support.apple.com/kb/HT4259

Your AirPort Extreme produces a dual band network with both a 2.4 GHz and 5 GHz signal. If you want to be able to extend both bands, you need another AirPort Extreme.

While an AirPort Express could be used, it will only extend one band...either 2.4 GHz or 5 GHz....but not both at once.

In general, a good location for an extending device is a point that is about half the distance from your "main" router to the area that needs more wireless coverage.

Depending on walls and other obstructions, you may need to experiment with placement of the extending device for best results.

Apple's step by step instructions to "Extend a wireless network" are in this support document, which assumes that you are using AirPort Utility version 5.x.

http://support.apple.com/kb/HT4259

If you are using Lion, you should download and install AirPort Utility 5.6 for Mac OS X Lion to track the instructions.

I have a problem ...

I have 2 airport extreme. With the first one I create the two network 2.4 & 5 Ghz. With the second one or I extend the 2.4 or the 5 ghz network. How can I configure it to extend both bands ?

What is the model number of the second AirPort Extreme?  Check the label on the bottom of the device if you are not sure what it is.

Also, check the first Extreme to make sure that both 2.4 GHz and 5 GHz bands are using the same wireless network name. You cannot assign a separate name to the 5 GHz network if you want to be able to extend both bands.

I have put the same name but it looks to extend the 2.4GHz only

Sorry cannot find the model number, but it has to be a "AirPort Extreme 802.11n (4th Gen)".

(Verified with serial number)

If the "main" Airport Extreme is set to use the same name for both the 2.4 GHz and 5 GHz bands, and the "remote" Extreme is configured to "Extend" that same wireless network name, then the AirPort Extremes are setup correctly.

5 GHz signals are much weaker than 2.4 GHz signals, so they do not pass through walls or other obstructions well.

You will likely need to locate the "remote" AirPort Extreme much closer to the "main" AirPort Extreme for this reason. Try to minimize the number of walls or other obstructions like a ceiling (which is much thicker than a wall, so it absorbs much more of the signal) between the AirPort Extremes.

If you still cannot get the "remote" AirPort Extreme to extend both bands, you may need to consider connecting the AirPort Extreme with a wired Ethernet cable to accomplish your goals.

That' not the way it worked for me just now. I have an older Airport Extreme set up using  different names for the 2.4GHz 802.11g and the 5GHz 802.11n networks.

I bought the brand new Airport Express and while both devices were in the same room used the AirPort Utility v6.1 to automatically extend the existing network. It showed me the name of the 2.4GHz network.

Then when I moved the new Airport Express to a different room it resynched and now I see both a 2.4GHz 802.11n and a 5GHz 802.11n with very strong signals and each has it own correct name. Using iStumbler I can also see weaker signals from the two networks coming off the old Airport Extreme base station.

So it eems to be working perfectly as expected.

I cannot duplicate this using either a manual or assisted setup, and Apple support says the same.

Congrats if you are able to do this.