An ISP RADIUS setup consists of :
- RADIUS Server
- NAS (one or more)
- Database server
RADIUS Server usually is a Linux server running FreeRadius service with management web interface , it will handle the authorization , authentication & accounting functions.
A NAS could be any device that use RADIUS for authentication, a common example of a NAS is the Miktotik router.
Usually you can connect as much as you want of NASs to a single RADIUS server , and users can roam between those NASs.
Database server usually is a MySQL DB or any other DB server ,it is used to store users information , system configuration etc...
a database server can be installed on the same RADIUS server , but in some cases with big ISPs it is recommended to use a standalone database server.
Bellow is a typical network setup for a RADIUS server with 2 Mikrotik routers conntected to it:
