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

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.

I faced a similar problem (slow roaming - or no roaming at all) even with OSX 10.10.x - I have 2 AP, one Technicolor and one Cisco-Linksys connected to the same switch and broadcasting the same SSDI on different radio channels. After some investigation I found a solution. You must be sure you have exactly the same authentication settings on the Wireless interface of the APs. In my case one AP was WPA/WPA2 and the other one was WPA2 only. When I enabled WPA/WPA2 also on the second one my Macbook Pro started roaming correctly.