Gennaro Leo wrote:

Hi all, I installed FreeRadius and sent some Accounting Request through radclient but the server replies always with a CoA-NAK...

That doesn't happen. Accounting-Request packets get Accounting-Response answers. If you're sending a CoA-Request, you might get a CoA-ACK or a CoA-NAK. As *always*, read the debugging output.

how can I configure it to send CoA-ACK? Which file must be modified?

The debugging output tells you. Read it. Alan DeKok.