Using an AirPort Express to extend an AirPort Extreme's signal in 2.4 GHz from 5 GHz

Question

I have an older AirPort Extreme and a new AirPort Express. Now because the 2.4 GHz bandwidth is very crowded I want to switch the signal towards 5 GHz. However I have a number of devices that only operate in the 2.4 GHz range. These devices are however clustered together so that if I can place my AirPort Express in the middle of them I should be able to service them all. So my question is how do I make my AirPort Express extend a 5 GHz signal in 2.4 GHz range?

Answer 1

It should be as simple as just setting up each band individually. Remember to setup WDS for 5GHz on both access points to "extend" a network.

Answer 2

It should "just work". Just configure your Express to extend the network of the Extreme. The mid-2012 AirPort Express will automatically connect to the Extreme on whichever band the Extreme is on (or, if it's a simultaneous dual-band Extreme; it'll pick whichever band is better for the conditions) and will automatically make that network available over both 2.4GHz and 5GHz.

Note that Apple uses the "Extend the network" terminology to refer to using a wireless backhaul. If you have the ability to use a wired Ethernet backhaul between the APs, that would be best, because it saves wireless bandwidth for mobile devices that really need it. In that case you would just set up the Express to have the same wireless network name, wireless security type, and wireless network password as the Extreme has, and make the Express be just a bridge (both NAT and DHCP server OFF). See How can I get the same SSID for multiple access points? for more details of this setup.