How to enable faster WiFi Roaming with Mac OS X & Airport base stations

How can I change the way Macbooks roam on the WiFi network? I would like to speedup the roaming of Macs (and maybe other devices).

Is there a setting on the Airport base stations or in Mac OS to speedup AP switching for example?

Currently the network is built around 1 main Switch interconnecting 1 router and 4 Airport base stations using the same SSID:

• 3 dual band Airport base stations
• 1 Airport 2.4GHz base station

On the 5GHz band, there is no overlap as each base station uses its own channel.

On the 2.4GHz band there is a very slight overlap between 2 base stations which are at opposite sides and at different stories of the building.

You can change the system preferences for JoinMode and JoinModeFallback to be the following:

    JoinMode (String)
        Automatic
        Preferred
        Ranked
        Recent
        Strongest
    JoinModeFallback (String)
        Prompt
        JoinOpen
        KeepLooking
        DoNothing

Do this using the airport command:

/System/Library/PrivateFrameworks/Apple80211.framework/Versions/A/Resources/airport

Run the command to see the options, up the top you'll see a section on how to sec preferences.

For instance:

sudo /System/Library/PrivateFrameworks/Apple80211.framework/Versions/A/Resources/airport prefs joinMode=Strongest

Note, this preference isn’t permanent, so you may need to automate this or issue it for specific problem situations or network providers.

Apple has introduced roaming across it's ecosystem with iOS 8 and OS X 10.10. You don't need to do anything as it's turned on by default. So, you can just update your OS on the Airport basestations as well as install Yosemite to take advantage of the changes.

Prior Yosemite, I've not seen instructions on how to enable this so I believe it's part of the drivers that were updated for 10.10.

The software was designed to keep a fair connection alive as long as possible rather than hop around always looking for a better connection. Now that AirPlay and AirDrop and continuity exploit the MIMO antennas that are shipping across the Apple hardware ecosystem, we now get better roaming since the hardware is more capable.