Manual:$wgPutIPinRC

Details
Prescribes whether MediaWiki should log the IP addresses of its editors in  . Although there is no interface in the standard MediaWiki package for retrieving this information, it can be accessed using extensions; a database administrator can also run an SQL query to retrieve the IP addresses.

Current versions of the ext-CU>Special:MyLanguage/Extension:CheckUser|CheckUser extension do not rely on this setting. CheckUser stores its data in a separate  table.