Mobility Overview

The ExtremeWireless system allows up to 12 controllers on a network to discover each other and exchange information about a client session. This technique enables a wireless device user to roam seamlessly between different APs on different controllers.

The solution introduces the concept of a mobility manager; one controller on the network is designated as the mobility manager and all others are designated as mobility agents.

The wireless device keeps the IP address, and the service assignments it received from its home controller—the controller that it first connected to. The WLAN Service on each controller must have the same SSID and RF privacy parameter settings.

You have two options for choosing the mobility manager:

• Rely on SLP with DHCP (Dynamic Host Configuration Protocol) Option 78
• Define at the agent the IP address of the mobility manager. By explicitly defining the IP address, the agent and the mobility manager are able to find each other directly without using the SLP discovery mechanisms. Direct IP definition is recommended to provide tighter control of the registration steps for multi-domain installations.

The controller designated as the mobility manager:

• Is explicitly identified as the manager for a specific mobility domain. Agents connect to this manager to establish a mobility domain.
• Defines, at the agent, the IP address of the mobility manager, which allows for the bypass of SLP. Agents directly find and attempt to register with the mobility manager.
• Uses SLP, if this method is preferred, to register itself with the SLP Directory Agent as Extreme NetworksNet.
• Defines the registration behavior for a multi-controller mobility domain set:
  • Open mode — A new agent is automatically able to register itself with the mobility manager and immediately becomes part of the mobility domain.
  • Secure mode — The mobility manager does not allow a new agent to automatically register. Instead, the connection with the new agent is placed in a pending state until the administrator approves the new device.
• Listens for connection attempts from mobility agents.
• Establishes connections and sends a message to the mobility agent specifying the heartbeat interval, and the mobility manager's IP address if it receives a connection attempt from the agent.
• Sends regular heartbeat messages containing wireless device session changes and agent changes to the mobility agents and waits for a returned update message.
• Establishes a connection to an optional backup mobility manager that can be configured to back up the primary mobility manager.

The controller designated as a mobility agent does the following:

• Uses SLP or a statically configured IP address to locate the mobility manager.
• Defines at the agent the IP address of the mobility manager, which allows for the bypass of SLP. Agents directly find and attempt to register with the mobility manager.
• Attempts to establish a TCP/IP connection with the mobility manager.
• Connects to an optional backup mobility manager that can be configured to back up the primary mobility manager.
• Sends updates, in response to the heartbeat message, on the wireless device users and the data tunnels to the mobility manager.

If a controller configured as the mobility manager is lost, with a backup mobility manager configured, the following occurs:

• If enabled, the controller establishes a connection to the optional backup mobility manager. When a failure occurs, the backup manager becomes the primary manager and control tunnels are re-negotiated. The data tunnels are not affected. When the primary manager comes back online, the backup manager detects the higher priority manager and switches back to agent (passive) mode.

If a controller configured as the mobility manager is lost, without a backup mobility manager, the following occurs:

• Agent to agent connections remain active.
• The mobility agents continue to operate based on the mobility information last coordinated before the manager link was lost. The mobility location list remains relatively unaffected by the controller failure. Only entries associated with the failed controller are cleared from the registration list, and users that have roamed from the manager controller to other agents are terminated and required to re-register as local users with the agent where they are currently located.
• The data link between active controllers remains active after the loss of a mobility manager.
• Mobility agents continue to use the last set of mobility location lists to service known users.
• Existing users remain in the mobility scenario, and if the users are known to the mobility domain, they continue to be able to roam between connected controllers.
• New users become local at attaching controller.
• Roaming to another controller resets session.

The mobility network that includes all the wireless controllers and the APs is called the Mobility Domain.

Note

The mobility feature is not backward compatible. This means that all the controllers in the mobility domain must be running the most recent controller software release.