act_as_gateway

#!/bin/sh -e
#
# Firewall
#

INTERNAL_IFACE=eth0
EXTERNAL_IFACE=eth1

start(){
	PATH=/usr/sbin:/sbin:/bin:/usr/bin

	#
	# delete all existing rules.
	#
	iptables -F
	iptables -t nat -F
	iptables -t mangle -F
	iptables -X

	# Always accept loopback traffic
	iptables -A INPUT -i lo -j ACCEPT


	# Allow established connections, and those not coming from the outside
	iptables -A INPUT -m state --state ESTABLISHED,RELATED -j ACCEPT
	iptables -A INPUT -m state --state NEW -i ! $EXTERNAL_IFACE -j ACCEPT
	iptables -A FORWARD -i $EXTERNAL_IFACE -o $INTERNAL_IFACE -m state --state ESTABLISHED,RELATED -j ACCEPT
	iptables -A INPUT -p tcp --dport 22 -j ACCEPT

	# Allow outgoing connections from the LAN side.
	iptables -A FORWARD -i $INTERNAL_IFACE -o $EXTERNAL_IFACE -j ACCEPT

	# Masquerade.
	iptables -t nat -A POSTROUTING -o $EXTERNAL_IFACE -j MASQUERADE

	# Don't forward from the outside to the inside.
	iptables -A FORWARD -i $EXTERNAL_IFACE -o $EXTERNAL_IFACE -j REJECT

	# Enable routing.
	echo 1 > /proc/sys/net/ipv4/ip_forward
}

stop(){
	#
	# delete all existing rules.
	#
	iptables -F
	iptables -t nat -F
	iptables -t mangle -F
	iptables -X

	# Disable routing.
	echo 0 > /proc/sys/net/ipv4/ip_forward
}
case "$1" in
    start)
	start
        ;;
    stop)
	stop
        ;;
    restart)
	stop ; start
        ;;
    *)
        echo "Usage: $0 {start|stop|restart}" >&2
        exit 1
        ;;
esac