Cookies: $wgCookieSetOnIpBlock
Determines whether to set a cookie when an IP user is blocked. Doing so means that a blocked user, even after moving to a new IP address, will still be blocked.
Introduced in version:1.32.0 (Gerrit change 433624; git #e8063a08)
Removed in version:still in use
Allowed values:(boolean)
Default value:true (1.34+)
false (1.32-1.33)

The cookie will contain an authentication code if $wgSecretKey is set, or otherwise will just be the block ID (in which case there is a possibility of an attacker discovering the names of revdeleted users, so it is best to use this in conjunction with $wgSecretKey being set).