This plugin logs the IP addresses of players as they log in, with commands allowing you to look-up the ip addresses a player has used or all of the players associated with an IP address.
Typing /ip or /ip help will display the help page - a list of all of the following commands.
Just put the JAR in the plugins folder, IPs will be tracked on player login and saved to the data folder.
save-delay - This determines how often (in minutes) the IP data should be saved to the data folder. This is to prevent the data from saving too many times if multiple people log in quickly. IPs will also be saved on plugin disable. A value of anything less than 1 minute will only save on plugin disable.
convert-automatically - This determines if the plugin should automatically convert the IP/Player logs to CSVs whenever it saves to the data folder. If this is false, the files will only ever be converted when the /ip convert command is run. convert-type determines which excel file will be generated.
track-history-limit - Limit the number of dates saved by the plugin.
display-login-message - Display the ip addresses of players as they login to players with the right permission.