Task: Disable / Turn off Linux Firewall (Red hat/CentOS/Fedora Core)

Type the following two commands (you must login as the root user):
# /etc/init.d/iptables save
# /etc/init.d/iptables stop

Task: Enable / Turn on Linux Firewall (Red hat/CentOS/Fedora Core)

Type the following command to turn on iptables firewall:
# /etc/init.d/iptables start

Other Linux distribution

If you are using other Linux distribution such as Debian / Ubuntu / Suse Linux etc, try following generic procedure.
Save firewall rules
# iptables-save > /root/firewall.rules
OR
$ sudo iptables-save > /root/firewall.rules
Now type the following commands (login as root):
# iptables -X
# iptables -t nat -F
# iptables -t nat -X
# iptables -t mangle -F
# iptables -t mangle -X
# iptables -P INPUT ACCEPT
# iptables -P FORWARD ACCEPT
# iptables -P OUTPUT ACCEPT
To restore or turn on firewall type the following command:
# iptables-restore < /root/firewall.rules