EAP devices can request controller IP via option 138 through DHCP. Take Branch 1 as example. Suppose the DHCP server in Branch 1 is capable of configure variable DHCP options. Set the controller IP, in our example, 192.0.2.2 as the option 138 value on it. All the EAP devices in the local network will be able to set 192.0.2.2 as the controller IP automatically after it boots up.