mod reuqest
 

In a nutshell, the mod checks if anyone that has registered has a more than 1 account on file on the forums.
Most forums such as mine often don't want people to have more than one account, or "bypassing" the ban barrier. I think this would help out.

I believe that I have seen a mod that does that at the mod section. Have a look there.

There really is no perfect way to do that, because someone who wants to register another account can find a way to do it from a different ip address and there's no way to tell. Also, there are reasons why two legitimate accounts might have the same ip address (like two people who live in the same house). That said, there's this mod that checks for duplicate ips: https://vborg.vbsupport.ru/showthread.php?t=282525