Do I need to create 2.4 & 5GHz networks manually with dual-band Airport Extreme?

Question

I'm thinking of getting Airport Extreme dual-band version, because specs say that it offers 2 separate networks: 2.4 & 5 GHz. This setup would work great at my place, since I have mix of G and N devices.

Now, to implement this, do I need to create two separate networks, or I join one network and AEBS decides which band to assign?

This is direct quote from the manual, but it feels bit vague: "Wireless devices join the network that provides them the best performance and compatibility, and the AirPort Extreme shares your broadband Internet connection with computers and devices on your network."

Answer 1

when you setup the router, you have a choice of creating one network per frequency or one singular ssid that supports both frequencies. in the former, you manually select which network you want to use. in the latter, the client device picks whichever it supports.

see http://www.engadget.com/2009/05/01/how-to-set-up-dual-band-wifi-and-juice-your-downloads/ for a clearer explanation.