WLANs can be configured to use the same or different Dynamic Host Configuration Protocol (DHCP) servers or no DHCP server. Two types of DHCP servers are available: internal and external.
Internal DHCP Server
The controllers contain an internal DHCP server. This server is typically used in branch offices that do not already have a DHCP server. The wireless network generally contains 10 access points or fewer, with the access points on the same IP subnet as the controller. The internal server provides DHCP addresses to wireless clients, direct-connect access points, appliance-mode access points on the management interface, and DHCP requests that are relayed from access points. Only lightweight access points are supported. When you want to use the internal DHCP server, you must set the management interface IP address of the controller as the DHCP server IP address.
DHCP option 43 is not supported on the internal server. Therefore, the access point must use an alternative method to locate the management interface IP address of the controller, such as local subnet broadcast, DNS, priming, or over-the-air discovery.
Note The controller internal DHCP server does not support Aironet 600 Series OfficeExtend Access Point.
Did you configure the DHCP address under the dynamic interface configuration or on WLAN ?
If DHCP server is not the WLC then did you also put the IP helper command the the VLAN on switch ?
or are you using internal DHCP server on WLC ? If yes then did you enable DHCP proxy ?
Check these option and let us know.
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Prevent IP address conflicts on your wireless network by managing DHCP scopes.
Please have a look into the Deployment guide.