The following article describes various ways to block IPs using the built-in RedHat firewall, iptables. The following command will drop all incoming connections from IP xx.xx.xx.xx:
iptables -I INPUT -s xx.xx.xx.xx -j DROP
To block a range, such as xx.xx.xx.* specify the CIDR block as follows:
iptables -I INPUT -s xx.xx.xx.0/24 -j DROP
If you wanted to later remove this entry you would replace...
By samantha, January 24, 2015