iptables -t filter -I INPUT -s 1.2.3.4/32 -j DROP
or
firewall-cmd \
--direct \
--add-rule ipv4 filter INPUT_direct 0 -s 1.2.3.4/32 -j DROP
or permanantly
firewall-cmd \
--permanent \
--direct \
--add-rule ipv4 filter INPUT_direct 0 -s 1.2.3.4/32 -j DROP