A method and device for ensuring address information of a wireless terminal device in a wireless local area network, the network comprising; an access point for setting up a communication connection to the terminal device, the method comprising establishing a communication connection between the terminal device and the access point (101), and relaying data packets from the terminal device to the network and from the network to the terminal device (105). The method further comprising the steps at the access point: detecting an IP address of the terminal device in response to the established communication connection (103), associating the detected IP address of the terminal device to the MAC address of the terminal device (104), and comparing that the address information of the terminal device on the relayed data packets are corresponding to the associated address information (111, 112).