nat.sh

#!/bin/bash

function print_help() {
	echo "Easy 4-step NAT tool"
	echo "Usage: $0 internal-dev external-dev ip-range"
	echo ""
	echo "internal-dev      e.g. eth0"
	echo "external-dev      e.g. wlan0"
	echo "ip-range          e.g. 192.168.0.1/24"
}

if [[ $BASH_ARGC < 3 ]]; then
	print_help
else
	echo -n "Enabling ip_forward in /proc/sys/net/"
	echo 1 > /proc/sys/net/ipv4/ip_forward
	echo "."

	echo -n "Setting firewall rules... "
	iptables -A FORWARD -i "$2" -o "$1" -m state --state RELATED,ESTABLISHED -j ACCEPT
	iptables -A FORWARD -i "$1" -o "$2" -j ACCEPT
	iptables -t nat -A POSTROUTING -s "$3" -o "$2" -j MASQUERADE
	echo "done."
	echo "You have just enabled NAT from $1 to $2 using range $3"
fi