The IP filters act as firewall following the white list principle, i.e. all data packets are blocked unless they are explicitly permitted here.
Click in the
Network → Firewall / NAT menu in the Firewall section on 
and check the checkbox IP filter for IPv4 activated.Click on SUBMIT .
Click on ACTIVATE PROFILE
.
Please note!
It is recommended to check all existing filter rules for their necessity and Restrict or deactivate IP Filter (Firewall) Rules them further, if applicable.