IP Range Transparent Proxy Script

# Firewall settings

for MASK in ...IP RANGE...; do
    iptables -t nat -A PREROUTING -i "$LAN_IFACE" -s "$LAN_TYPE.$MASK" -p tcp --dport 80 -j DNAT --to "$PROXY_IP:$PROXY_PORT"
    iptables -I FORWARD -s "$LAN_TYPE.$MASK" -d ! "$LAN_NET" -p tcp -j DROP
    iptables -I FORWARD -d "$LAN_TYPE.$MASK" -s ! "$LAN_NET" -p tcp -j DROP
done

# Startup settings

while :; do nc -l -p $PROXY_PORT -e /path/to/proxy_script; done &

# Proxy script

# read headers

if [ "$HTTP_HOST" == "$SERVER" ]; then
    echo "HTTP/1.0 403 Forbidden"
else
    echo "HTTP/1.0 307 Temporary Redirect"
    echo "Location: http://$SERVER/"
fi

cat <<EOF
Content-Type: text/html; charset=UTF-8

<html>
<head>
...
EOF