Wireless – Controller Discovery Process

In a CAPWAP environment, a lightweight access point discovers a controller by using CAPWAP discovery mechanisms and then sends it a CAPWAP join request. The controller sends the access point a CAPWAP join response allowing the access point to join the controller. When the access point joins
the controller, the controller manages its configuration, firmware, control transactions, and data transactions.

Lightweight access points must be discovered by a controller before they can become an active part of the network. The lightweight access points support the following controller discovery processes:

• Layer 3 CAPWAP or LWAPP discovery — Can occur on different subnets from the access point and uses IP addresses and UDP packets rather than the MAC addresses used by Layer 2 discovery.

• Over-the-air provisioning (OTAP)—This feature is supported by Cisco 4400 series controllers. If this feature is enabled on the controller (in the controller General page), all associated access points transmit wireless CAPWAP or LWAPP neighbor messages, and new access points receive the controller IP address from these messages. This feature is disabled by default and should remain disabled when all access points are installed.

• Locally stored controller IP address discovery—If the access point was previously associated to a controller, the IP addresses of the primary, secondary, and tertiary controllers are stored in the non-volatile memory of an access point. This process of storing controller IP addresses on access points for later deployment is called priming the access point.

• DHCP server discovery—This feature uses DHCP option 43 to provide controller IP addresses to the access points. Cisco switches support a DHCP server option that is typically used for this capability.

• DNS discovery—The access point can discover controllers through your domain name server (DNS). For the access point to do so, you must configure your DNS to return controller IP addresses in response to CISCO-CAPWAP-CONTROLLER.localdomain or CISCO-LWAPP-CONTROLLER.localdomain, where localdomain is the access point domain name.
When an access point receives an IP address and DNS information from a DHCP server, it contacts the DNS to resolve CISCO-CAPWAP-CONTROLLER.localdomain or CISCO-LWAPP-CONTROLLER.localdomain. When the DNS sends a list of controller IP addresses, the access point sends discovery requests to the controllers.

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