Wi-Fi Tip: AP Join in a Pinch

Ever been in an emergency situation where you need to get an AP up in
a hurry? Perhaps you didn't configure DHCP Option 43 b/c you have a
gizillion scopes, or the DNS name b/c of a common suffix across
multiple sites. Try this...

On the default gateway device (router or L3 switch) issue these

ip forward-protocol udp 12223

ip forward-protocol udp 5246

interface GigabitEthernet0/0

   ! Define the helper address for the DHCP

   ! server so APs can obtain an IP address

   ip helper-address

   ! Define the helper address for the WLC

   ! to forwarded LWAPP/CAPWAP discovery broadcasts

   ip helper-address

Configure the interface attached to the subnet the AP is connected to,
and use the controller's management interface as the helper address.

These commands tell the router to forward LWAPP and CAPWAP control
broadcast frames, including discovery requests, to configured ip
helpers which now includes the controller!

You should see the AP discover and join the controller within seconds
as if they were on the same subnet.