12-19-2007 11:20 AM - edited 07-03-2021 03:07 PM
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!
12-19-2007 07:38 PM
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 âcisco-lwapp-controllerâ
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
12-19-2007 08:03 PM
Excellent. Thanks Rob.
12-20-2007 06:30 AM
You are most welcome Kevin!
Happy Holidays :)
Rob
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