linux – Routing between two interfaces on Raspberry

do have these physical interfaces on my PI

eth0      Link encap:Ethernet  HWaddr b8:27:eb:8b:d9:d4
          inet addr:  Bcast:  Mask:

wlan1     Link encap:Ethernet  HWaddr b8:27:eb:de:8c:81
          inet addr:  Bcast:  Mask:

a tunnel is build up with VPN to what creates an additional tunnelinterface on eth0

tun0      Link encap:UNSPEC  HWaddr 00-00-00-00-00-00-00-00-00-00-00-00-00-00-00-00
          inet addr:  P-t-P:  Mask:
          inet6 addr: fe80::f2a9:c54f:ad3f:2296/64 Scope:Link

wlan1 is WLAN Access point.

Routing is enabled:

pi@raspberrypi:/ $ cat /proc/sys/net/ipv4/ip_forward

Routes are set up as following:

pi@raspberrypi:/ $ route
Kernel IP routing table
Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
default         *              U     0      0        0 tun0
xxxxxxxxx.dip0. UGH   0      0        0 eth0     *        U     202    0        0 eth0   UG    0      0        0 wlan1

Due to the first answer here I added also

sudo iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE
sudo iptables -A FORWARD -i tun0 -o wlan1 -m state --state RELATED,ESTABLISHED -                                                                                          j ACCEPT
sudo iptables -A FORWARD -i wlan1 -o tun0 -j ACCEPT

to /etc/iptables.ipv4.nat


Clients in the WIFI on WLAN1 having IP adresses from (default gw = of course) can connect to the PI on there interface.

But still neither routing to the other network on the PI ( nor other addresses is working.

So my target routing all traffic over the tunnel is not possible.

Any ideas?