dial up users authentication problem

Hi, I have two group of users connected to internet through a firewall for traffic control. Both should be authenticated by firewall through a RADIUS server before connecting to internet and there are different user policies for different users in firewall. 1) LAN users. 2) Dial-up users which are connected to a router, and are authenticated by a RADIUS server (for logging in) The problem is that I don't want a second authentication in firewall. I want the users logged in, can be automatically authenticated by the firewall. Firewall should somehow know their username to apply the policies. I think there should be a mapping from IP to username in RADIUS server. Is this possible? If yes, please tell me how.