Correct way to achieve groups of users and confirm access to specific clients

Hello, I run a FreeRADIUS Ver.:2.1.1. (as it come with SLES11) Configured as User-Source are LDAP (eDir) and the text file (users). There are a lot of clients in the client file. (I assume they are called NAS in RADIUS?!) Now I want to achieve that users are in groups and these groups should access only specific clients. I know that I can setup group(s) in LDAP and restrict RADIUS to search for those users only which are member of this group(s) Q1: But for which words I have to search to group my text file users? Q2: Is it possible to configure more than one LDAP section to achieve that different LDAP groups get access to specific clients? Or what is the correct way? TiA Bernd