RedHat and other RedHat flavours
First login as the root user.
Next enter the following three commands to disable firewall.
# service iptables save
# service iptables stop
# chkconfig iptables off
If you are using IPv6 firewall, enter:
# service ip6tables save
# service ip6tables stop
# chkconfig ip6tables off
Ubuntu
$ sudo iptables -X
$ sudo iptables -t nat -F
$ sudo iptables -t nat -X
$ sudo iptables -t mangle -F
$ sudo iptables -t mangle -X
$ sudo iptables -P INPUT ACCEPT
$ sudo iptables -P FORWARD ACCEPT
$ sudo iptables -P OUTPUT ACCEPT
sudo ufw disable