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How does CAPWAP work when an LAP and WLC are not on the same subnet?

Reading various Cisco documentation and Vinay Sharma’s document ("AP fails to join controller" - Lightweight Access Point (LAP) fails to join Wireless LAN controller (WLC  https://supportforums.cisco.com/document/69341/ap-fails-join-controller-lightweight-access-point-lap-fails-join-wireless-lan), I understand:

 

“When the LAP powers up, it sends out a DHCP request, with the hope that a DHCP server will provide an IP address. After the LAP gets an IP address from the DHCP server, the LAP broadcasts a Layer 3 LWAPP discovery message on to its local subnet. Because the WLC is also on the same subnet, the WLC receives the LWAPP discovery request from the LAP and responds with a Layer 3 LWAPP discovery response.”

 

Questions:

  1. What happens if the LAP and the WLC are not on the same subnet?  By default, a router/layer 3 device will STOP all broadcast. 
  2. How does CAPWAP/LWAPP get around this?  In our network, no LAP is on the same subnet as the WLC.  So I am not sure how they are working. 

 

Thank you

 

T.J. Reed

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