TYPO3 Core

If a FE-user logs in TYPO3 saves the first two parts of the IP (e.g. 123.45 from 123.45.67.89) in the session-variable.
If in the same session (saved by a cookie) a request arrives from another IP the user will not be authenticated.
This regards to all call-by-call-users or users with providers which change the IP with every new internet-connection.

Solution:
in phpMyAdmin execute this:
ALTER TABLE `fe_users` ADD `disableIPlock` INT DEFAULT '1' NOT NULL ;
If this flag is set TYPO3 saves the string '[DISABLED]' in fe_sessions.sys_iplock and spares the check.
be_users.disableIPLock exists by default, fe_users.disableIPLock is missing

(issue imported from #M1674)