Normally, the WLAN stack sends a RADIUS "accounting start" message as soon as the WLAN client is connected. Often the WLAN client has no IP address at this time, most likely because one has not yet been issued by the DHCP server. Consequently the "Framed-IP-Address" attribute in the RADIUS accounting message may lack meaningful content.
As of LCOS version 9.18 RU1, the accounting start message is optionally generated only after the client has received a valid IP address. In this case the RADIUS accounting server always receives a valid framed IP address.