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The Controller Discovery Process
The access point uses standard Control and Provisioning of Wireless Access Points Protocol (CAPWAP) to communicate
between the controller and other wireless access points on the network. CAPWAP is a standard, interoperable protocol which
enables an access controller to manage a collection of wireless termination points. The discovery process using CAPWAP is
identical to the Lightweight Access Point Protocol (LWAPP) used with previous Cisco Aironet access points. LWAPP-enabled
access points are compatible with CAPWAP, and conversion to a CAPWAP controller is seamless. Deployments can combine
CAPWAP and LWAPP software on the controllers.
The functionality provided by the controller does not change except for customers who have Layer 2 deployments, which
CAPWAP does not support.
In a CAPWAP environment, a wireless 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.
Note For additional information about the discovery process and CAPWAP, see the Cisco Wireless LAN Controller Software
Configuration Guide. This document is available on Cisco.com.
Note CAPWAP support is provided in controller software release 5.2 or later. However, your controller must be running
release 7.5.x.x or later to support 700 series access points.
Note You cannot edit or query any access point using the controller CLI if the name of the access point contains a space.
Note Make sure that the controller is set to the current time. If the controller is set to a time that has already occurred, the
access point might not join the controller because its certificate may not be valid for that time.
Access points must discovered a controller before they can become an active part of the network. The access point supports
these controller discovery processes:
• Layer 3 CAPWAP discovery—The access point performs a local broadcast (255.255.255.255) discovery request to find any
contollers on the same subnet/vlan. The request can be forwarded to other networks by the IP helper featuer that is present
on switches and router.
• Locally stored controller IP address discovery—If the access point was previously joined to a controller, the IP addresses of
the primary, secondary, and tertiary controllers are stored in the access point’s non-volatile memory. This process of storing
controller IP addresses on an access point for later deployment is called priming the access point. For more information
about priming, see the “Performing a Pre-Installation Configuration” section on page 8.
• 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. For more information about DHCP option
43, see the “Configuring DHCP Option 43 and DHCP Option 60” section on page 23.
• 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, where localdomain is the access point domain name. Configuring the
CISCO-CAPWAP-CONTROLLER provides backwards compatibility in an existing customer deployment. 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. When the DNS sends a list of controller IP addresses, the access point
sends discovery requests to the controllers.