How to block IP address in Linux via ssh:

The following command will drop any packet coming from the IP address 1.2.3.4:

iptables -I INPUT -s 1.2.3.4 -j DROP

or you can use append


iptables -A INPUT  -s 1.2.3.4 -j DROP


How Do I Block Subnet (xx.yy.zz.ww/ss)?

Use the following syntax to block 10.0.0.0/8 on eth1 public interface:
iptables -i eth1 -A INPUT -s 10.0.0.0/8 -j DROP

How Do I View Blocked IP Address?

Simply use the following command:
iptables -L -v

How Do I Save Blocked IP Address?
service iptables save