Session Availability

Session availability enables wireless APs to switch over to a standby (secondary) wireless controller fast enough to maintain the mobile user‘s session availability in the following scenarios:

• The primary wireless controller fails (see AP Fail Over When Primary Controller Fails).
  

  AP Fail Over When Primary Controller Fails

  
• The wireless AP‘s network connectivity to the primary controller fails (see AP Fail Over When Connectivity to Primary Fails).

The secondary controller does not have to detect its link failure with the primary controller for the session availability to kick in. If the AP loses five consecutive polls to the primary controller either due to the controller outage or connectivity failure, it fails over to the secondary controller fast enough to maintain the user session.

In session availability mode (Session Availability Mode), the APs connect to both the primary and secondary controllers. While the connectivity to the primary controller is via the “active” tunnel, the connectivity to the secondary controller is via the “backup” tunnel.

The following is the traffic flow of the topology illustrated in Session Availability Mode:

• The AP establishes the active tunnel to connect to the primary controller.
• The controller sends the configuration to the AP. This configuration also contains the port information of the secondary controller.
• On the basis of the secondary controller‘s port information, the AP connects to the secondary controller via the backup tunnel.
• After the connection is established via the backup tunnel, the secondary controller sends the backup configuration to the wireless AP.
• The AP receives the backup configuration and stores it in its memory to use it for failing over to the secondary controller. All this while, the AP is connected to the primary controller via the ‘active‘ tunnel.

Session availability applies only to the following topologies:

• Bridge Traffic Locally at Controller
• Bridge Traffic Locally at AP