Please confirm that you have the Instant AP model (IAP), not the campus AP model (AP).
On the back, there should be a separate sticker that either shows:
- for the 105: AP-105, which means the AP requires a controller for operation, or IAP-105, which means it can run either as Instant AP, without a controller or can be converted to an campus AP with central controller.
- for the 225: AP-225 for the controller AP or IAP-225-RW, IAP-225-US, IAP-225-IL for the Instant version.
The campus AP models (AP) require a controller to operate The Instant models (IAP) can work either with, or without a controller.
Campus APs cannot be converted to Instant AP, by purpose (regulatory and theft control).
If you confirmed that it is an Instant model, indeed you need DHCP, or use the console to set a static IP for the AP.