Lancom WLC-4006 Manual page 111

LANCOM WLC series
Chapter 4: Configuring the WLAN Controller
110
In the WLAN controller's RADIUS server, define an "empty realm"
(e.g. "COMPANY.EU"). This realm is attached to all user names which
request authentication from the WLAN controller and which do not
already have a realm. In this application, the internal users have no realm
defined. In order to prevent the WLAN controller's RADIUS server from
attaching a realm, the "Default realm" field must be left empty.