Actual methods of searching for illegal clients on the Internet?

Question

Computer networks

Tell me what are the methods, software and other tools for finding illegal clients.
If you look at statistics on a specific port, what should you pay attention to?
Are there any methods to see the number of clients behind the subscriber's router, all packets that go through the router are already signed by it?
All options, ideas, schemes from life, etc. are needed.

The bottom line is this, we connect the subscriber, and the subscriber himself is already distributing the Internet to half the entrance. How to track it?

Thanks in advance !

Answer 1

What does "non-legal" mean (and for God's sake, write this word without errors)?
What kind of "Internet" clients do you need to find?

Answer 2

correctly and clearly formulate what exactly you want and who is an "illegal Internet client" for you

Answer 3

I don't even want to think about a question with so many errors

Answer 4

www.forensicswiki.org/wiki/NAT_detection