Wireless - virtual WLC limitations
A wireless controller or WLC can be deployed as a virtual device, or a vWLC. However, when this is done, it has some limitations compared to a physical WLC. Specifically, a virtual WLC has a limited supported feature set.
With a vWLC, you can only configure access points in FlexConnect mode. This means that other modes such as sniffer, monitor, or rogue detector are not available.