Procedure to test performance

Hello My radius server is not implemented yet, but i am wondering of a performance of it before it starts, I will need to simulate a performance test, My idea is to generate packet to analize the server. 1. If anyone done that before, could you give some clues of how to test it, and what to focus on. 2. Is there a ready tool to do that for me? (i've heard about it, but cannot find it) 3. In your experience of bad performace what to focus on to improve it? Interfaces, RAM or proessor ? Cheers Pawel Cieplinski