net-forward

#!/bin/bash

from=eth0
to=wlan0

lock=/tmp/net_forward_lock
name=$(basename "$0")

if [[ "$#" = "1" && "$1" = "on" ]]
then
	if [ -f "$lock" ]
	then
		echo Network forwarding is already on.
		exit 1
	else
		sudo ifconfig $from 192.168.10.1 up

		sudo iptables -A FORWARD -i $from -o $to -s 192.168.10.0/24 \
			-m conntrack --ctstate NEW -j ACCEPT
		sudo iptables -A FORWARD \
			-m conntrack --ctstate ESTABLISHED,RELATED -j ACCEPT
		sudo iptables -A POSTROUTING -t nat -j MASQUERADE
		sudo sh -c "echo 1 > /proc/sys/net/ipv4/ip_forward"

		sudo systemctl start isc-dhcp-server.service

		sudo touch $lock
		echo Network forwarding is turned on.
	fi
elif [[ "$#" = "1" && "$1" = "off" ]]
then
	if [ -f "$lock" ]
	then
		sudo iptables -D FORWARD -i $from -o $to -s 192.168.10.0/24 \
			-m conntrack --ctstate NEW -j ACCEPT
		sudo iptables -D FORWARD \
			-m conntrack --ctstate ESTABLISHED,RELATED -j ACCEPT
		sudo iptables -D POSTROUTING -t nat -j MASQUERADE
		sudo sh -c "echo 0 > /proc/sys/net/ipv4/ip_forward"

		sudo systemctl stop isc-dhcp-server.service

		sudo rm -f $lock
		echo Network forwarding is turned off.
	else
		echo Network forwarding is already off.
		exit 1
	fi
else
	echo "Usage: $name on | off"
	exit 1
fi

exit 0