LWAPP discovery - what's in the APs list of controllers

Unanswered Question

Hello networkers!

I know the AP goes through a series of steps to discover a controller. I've read that it checks DHCP Option 43 **BEFORE** checking DNS for CISCO-LWAPP-CONTROLLER.localdomain. And, the AP compiles a list of candidate controllers.

My question is:

Does it use BOTH the set of controllers given in DHCP Option 43 -AND- in DNS? Or, if it sees an Option 43, does the discovery end there?

Thanks much!

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Rob Huffman Wed, 12/19/2007 - 19:38

Hi Kevin,

Excellent question! The LWAPP Discovery does not end there as it essentially wants as many candidate Contollers as possible. Have a look;

The LWAPP Layer 3 WLC discovery algorithm repeats until at least one WLC is found and joined.

Note: During the LWAPP Layer 3 WLC discovery, the AP **always completes all steps 1 through 5 (discovery type: broadcast, configured, OTAP, dhcp server and dns)

in this section in order to build a list of candidate WLCs. After the AP has completed the LWAPP WLC discovery steps, the AP selects a WLC from the candidate WLC list on the basis of certain criteria, and then sends that WLC an LWAPP join request.

From this good doc;

http://www.cisco.com/en/US/tech/tk722/tk809/technologies_tech_note09186a00806c9e51.shtml#topic2

The LWAPP AP goes through this process on startup for Layer 3 mode:

The LAP boots and DHCPs an IP address if it was not previously assigned a static IP address.

The LAP sends discovery requests to controllers through the various discovery algorithms and builds a controller list. Essentially, the LAP learns as many management interface addresses for the controller list as possible via:

DHCP option 43 (

DNS entry for “cisco-lwapp-controller”

Management IP addresses of controllers the LAP remembers previously

A Layer 3 broadcast on the subnet

Over the air provisioning

Statically configured information

http://www.cisco.com/en/US/products/ps6366/products_tech_note09186a00808f8599.shtml#backinfo

Hope this helps!

Rob

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