Hi,
The RADIUS server can't assign IP addresses to the L2TP users.
When RADIUS authentication is used and the RADIUS server is configured with the Frame-IP and Frame-Route attributes for users, the LNS delivers the Frame-IP and Frame-Route attributes to the dial-up user (But the Frame-IP attribute must be in the local address pool.)
That is, the RADIUS server can be used to control the addresses that users obtain. However, the LNS still needs to configure the addresses.