I present to you a plugin that saves the name of the players in a file with the IP address. Let's consider it calmly: The player entered:

In the plugin folder, 2 folders are created: ips and players:


In the Players folder, files with player nicknames are created and all the IP addresses of the user through which he accessed the server will be recorded in the file:

In the ips folder there is a more interesting situation:

A file with an IP address is created there and detailed information will be indicated in the file

Also, to make it easier for administrators, a command system was added
/ps ip %ip%
/ps player %nick%

It simply shows the last 20 lines of the file you specified.
If you want use this commands in minecraft, you need permission:
- ps.use