#!/bin/sh
INADDR=$1
INPORT=$2
OUTADDR=$3
OUTPORT=$4

usage()
{
    echo "Usage: $0 INADDR INPORT OUTADDR OUTPORT"
    echo ""
    echo "NAT policies can be seen with"
    echo "       iptables -t nat -n -L"
    echo "... and remember to allow port forwarding!"
    echo "       echo 1  > /proc/sys/net/ipv4/ip_forward"
    exit
}

if [ "$1 " = " " ]; then
	usage
fi

echo "Stopping firewall and allowing everyone..."
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

echo "Incoming TCP connection for ${INADDR}:${INPORT} "
echo "will be redirected to ${OUTADDR}:${OUTPORT}"
echo "it's ok [y/n] ? "

read DATAIN
if [ ${DATAIN} = "y" ]; then
	iptables -t nat -A PREROUTING  -p tcp -m tcp -d ${INADDR} --dport ${INPORT} -j DNAT --to-destination ${OUTADDR}:${OUTPORT}
	iptables -t nat -A POSTROUTING -p tcp -d ${OUTADDR} --dport ${OUTPORT} -j MASQUERADE

echo	iptables -t nat -A PREROUTING  -p tcp -m tcp -d ${INADDR} --dport ${INPORT} -j DNAT --to-destination ${OUTADDR}:${OUTPORT}
echo	iptables -t nat -A POSTROUTING -p tcp -d ${OUTADDR} --dport ${OUTPORT} -j MASQUERADE
else
	echo "nothing done"
fi