A firewall is designed to help protect your computer from attack by malicious users or by malicious software (viruses that use unsolicited incoming network traffic to attack).

Also before you disable your firewall, you must disconnect your computer from all networks, including the Internet to avoid damage

You would like to Halt linux firewall or stop linux firewall (i.e. flush iptables rules). First login as root user.

Option A - If you are redhat Linux user type command:

If you are using Red Hat (RHEL) / CentOS / Fedora Core Linux, use the following command:

/etc/init.d/iptables stop

OR

service iptables stop

Option B - If you are Debian Linux user type following commands one by one

iptables -F
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