Cisco Wireless Controllers can be organised into mobility groups to help with intercontroller roaming.
If there are two controllers that are assigned to the same mobility group, clients will be able to quickly roam between them.
Layer 2 and Layer 3 roaming is supported for Mobility Groups along with the assistance technologies for roaming: CCKM, key caching and 802.11r
If there are two controllers assigned to different mobility groups, clients will still be able to roam between them but the roaming will not be as efficient.
Credentials will not be shared or cached so clients will need to go through the full authentication process to connect to the network
Each controller maintains a mobility list that contains its own MAC address plus the MAC addresses of the other controllers in it’s group.
The listing of the MAC address in the mobility group allows that controller to communicate with the other controller to assist in Layer 2 or Layer 3 roaming with the other controllers. If the controller does not have a record of another wireless controller and a client roams it, the anchor controller will not be able to assist with that roam and the client must go through the full authentication process.