cancel
Showing results for 
Search instead for 
Did you mean: 
cancel
Announcements
359
Views
0
Helpful
5
Replies
Highlighted
Beginner

Controller Discovery and AP States

Hi community,

 

While studing the controller discovery and AP states chapter in the CCNA Wireless OCG I got confused. Let me explain. These are the AP states:

 

apstates.PNG

 

I am fine with all the states except for points 2, 3 and 4. The OCG says the following:

 

apstates2.PNG

The question is, the AP attempr to build a CAPWAP tunnel (3) with all the WLCs discovered (2)? After CAPWAP tunnels have been built, the AP selects only a WLC from the list (4)? What happens if the AP has built CAPWAP tunnels with other WLCs if they are not going to be used? According to me, this would make sense if point 3 and 4 are switched, like this:

 

2. WLC discovery.

3. WLC join.

4. CAPWAP tunnel.

 

The AP would discovery WLCs (DHCP/DNS method, broadcast, etc.), it then would join one or more WLCs, and then it would build CAPWAP tunnels only to the WLCs it wants to join (and they have accepted and replied with a CAPWAP Join Response message) in the previous step. The AP wouldn't build CAPWAP tunnels with WLCs which are not going to be used. What am I missing?

 

Regards,

Julián

5 REPLIES 5
Beginner

Re: Controller Discovery and AP States

Hi guys,

 

When I continue reading the OCG I reach the WLC Selection section, which confirms my guess:

 

apstates3.PNG

From that excerpt, it seems the AP first discovers the WLCs, secondly select the WLCs it wants to join, and last it builds the corresponding DTLS/CAPWAP tunnels. Then, the order of steps 2, 3 and 4 (like Figure 11-1) showed in the previous message is wrong? Is it a mistake in the CCNA Wireless OCG?

 

Regards,

Julián

Beginner

Re: Controller Discovery and AP States

An AP will discover the WLC via one of 4 methods:

 

1] Static IP at the AP (called priming if manually configured, but also stored in NVRAM if AP has previously joined WLC)

2] DHCP Option 43

3] DNS request looking for CISCO-CAPWAP-CONTROLLER (or CISCO-LWAPP-CONTROLLER if using older code)

4] Subnet broadcast (if AP and WLC are on the same L2 segment)

 

Once an AP discovers the WLC(s) it will attempt to join ONE WLC only. It will not have multiple CAPWAP tunnels to all candidate WLCs.

 

Here's a good reference:

https://community.cisco.com/t5/wireless-mobility-documents/joining-process-of-an-cisco-access-point/ta-p/3149279

Beginner

Re: Controller Discovery and AP States

Hi guys,

 

Thanks for your replies. I am clear about the discovery process, my doubt is about the CAPWAP tunnel step. Few pages later, the OCG says again:

 

Tip When an AP boots and builds a list of potential controllers, it can use CAPWAP to
build a tunnel to more than one controller. The AP will join only one controller, which it
uses as the primary unit. By building a tunnel with a second controller ahead of time, before
the primary controller fails, the AP will not have to spend time building a tunnel to the
backup controller before joining it.

 

So I am not sure what is the correct answer? Any official documentation? The links you posted only refer to the discovery process but not the CAPWAP step.

 

Regards,

Julián

Beginner

Re: Controller Discovery and AP States

Hi,

Any idea?

Regards,
Julián
VIP Engager

Re: Controller Discovery and AP States

CreatePlease to create content
Content for Community-Ad
July's Community Spotlight Awards