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Capwap encapsulation

Hi all ,

Well to start with , this is a fundamental question/ doubt that i had ,  but never really cleared.

I know that WLAN are mapped on to Dynamic Interfaces .

Dynamic Interfaces are analogous to VLANS.

Suppose i have enabled :

A. Interface 1  => Vlan 2.

B. Interface 2  => Vlan 3.

Interface 1(vlan 2)     => SSID 2.

Interface 2(vlan 3)     => SSID 3.

Now when i go to the access layer and connect the Access Point , i connect my AP to switchport Tagged as Vlan 100.

My AP gets an IP of Vlan 100.

But even then the clients connected to my AP ( Suppose SSID 2) , get their IP Addresses belongin to VLAN 2. Even if VLAN 2 , is not present/configured in the access swicthes at all !

Now i understand that this is because the traffic from the AP gets encapsulated into CAPWAP Frames , so that the underlying VLAN information is invisible to the access layer switching infra.

But i need to know , how exactly does this happen. I mean how are the frames encapsulated / the format of the frames , especially the Destination/Source Mac/IP Addresses at each layer.

Thanks ,

Rahul.

4 REPLIES
Hall of Fame Super Silver

Capwap encapsulation

If the AP is in local mode, the switchport should be an access port not a trunk port.  All the traffic flows to the WLC and does not get put on the access switch it is connected to.  What you need to understand is that all traffic gets tunneled back to the WLC on the AP management ip address.  Vlan 1 and vlan 2 will be tunneled over vlan 100 since that is the vlan that your AP is on.

Thanks,

Scott

Help out other by using the rating system and marking answered questions as "Answered"

-Scott
*** Please rate helpful posts ***

Re: Capwap encapsulation

Great question and I had the same void in understanding when I started. The best thing you can do is sniff the traffic between the ap and the controller. In wireshark check box Cisco controller so wireshark can decode the capwap. Then you can peek inside the capwap packet.



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__________________________________________________________________________________________ "Satisfaction does not come from knowing the solution, it comes from knowing why." - Rosalind Franklin ___________________________________________________________
Silver

Re: Capwap encapsulation

New Member

Re: Capwap encapsulation

Ty Kashik , George , Scott .

Well as i dont have ready access to a AP , it will take some time.

But eventually i ll capture CAPWAP Frames and check it out !

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