Block IP with iptables

If u need to block a particular IP address within a linux firewall, than this command

iptables -A INPUT -s 65.55.44.100 -j DROP

remove rule from iptables
iptables -D INPUT -s 65.55.44.100 -j DROP

check iptables
iptables -S

Flush iptables
iptables -F

Iptables default command definition
sudo iptables -A -i < interface > -p < protocol (tcp/udp) > -s < source > --dport < port no. > -j < target >