Flush all iptables firewall rules:
#!/bin/sh
echo "Flushing firewall rules..."
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
Source: How to: Linux flush or remote all iptables rules - NixCraft