AP joining process (1.a) -- What is capwap?

Hello everyone

I want to introduce AP joining process as the following three parts.

(1.a)  What is capwap ?
(1.b)  Discovery mechanism
(1.c)  How to troubleshoot


OK,  Let us go to (1.a)  What is capwap ?

Control and Provisioning of Wireless Access Points (CAPWAP) is a standard and interoperable protocol that enables a Wireless LAN Controller (WLC) to manage access points (AP).

As shown in this picture, CAPWAP makes a channel between WLC and AP.  By using this "this capwap channel",  WLC and AP can talk to each other.




One of important purposes for CAPWAP is that builds AP joining process. The overview of this process:
Step 1:  Discovery request
Step 2:  Discovery response
Step 3:  DTLS session establishment
Step 4:  Join request
Step 5:  Join response
Step 6:  Configuration status request 
Step 7:  Configuration status response
Step 8:  Run state

The sequence of AP joining process will be like this.
 

As I had told you, the best way to study CCIE wireless is using magic tool "debug and packet capture".

If you give "debug capwap event enable" on WLC, you will see
Aug 6 : xx.xx.xx.xx.xx.xx CAPWAP State: Join
Aug 6 : xx.xx.xx.xx.xx.xx CAPWAP State: Configure
Aug 6 : xx.xx.xx.xx.xx.xx CAPWAP State: Run


Meanwhile,If you make wireshark packet capture between WLC and AP, you will the following result.
















As the summary,  CAPWAP is a very basic thing for Cisco Wireless LAN Controller.
I high recommend to read the following RFC documents about CAPWAP
1.  RFC 4546
2.  RFC 5415
3.  RFC 5415



Good Luck !!