client_id always unique and 5 numbers?

Because A7 commercial edition does not have a feature to kick people, i'm trying to make a plugin that allows to ban players.

Now about my questions:

#1 A client_id is always unique on a machine?
#2 The client_id is always 5 numbers?

Reason for asking it that when I run more than one client on the same machine as the server run on, it seemed to give each the same client_id, but could be wrong due to the way i'm filter players from the network. Wonder how the client_id is created. Does it use something from the system to make it unique?

You could create a user name and password system. People would login with a unique user name, which you could banned.

Yes I know and already made one with MySQL and PHP, but this time i'm making a standalone plugin with banfile. And needed to know the client_id. Anyways i'm able to get the client_id now. I just made some mistake with format strings.