How to access PLC from Windows via Raspberry Pi connected through OpenVPN Access Server?

Question

Device A (PLC, static IP=10.10.10.11) 
        |
        | eth0 connection 
        |
Device B (raspberry B 3,  Jessie)
        |
        | OpenVPN  
        |
Device C (laptop, Windows 8.1)

I am trying above setup.

The thing is Device B and Device C are OpenVPN clients connected to same OpenVPN access server.

My IP configurations are:

(Device A) PLC ---> 10.10.10.11 

(Device B)R-pi ---> 
cat /etc/dhcpcd.conf 

interface eth0 
static ip_address=10.10.10.10/24 
static domain_name_servers=192.168.1.1

VPN network IP= 10.8.0.2

(Device C) Windows 8.1 --->
VPN network IP= 10.8.0.5

I have enabled Static routes on router.

But I am unable to even ping Device A from Device C.

So what else should I change for this to work?

Output of:

ip addr

1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
    inet 127.0.0.1/8 scope host lo
       valid_lft forever preferred_lft forever
    inet6 ::1/128 scope host 
       valid_lft forever preferred_lft forever
2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP group default qlen 1000
    link/ether b8:27:eb:ef:04:1b brd ff:ff:ff:ff:ff:ff
    inet 10.10.10.10/24 brd 10.10.10.255 scope global eth0
       valid_lft forever preferred_lft forever
    inet6 fe80::e52b:ccb0:7b56:f2ea/64 scope link 
       valid_lft forever preferred_lft forever
3: wlan0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP group default qlen 1000
    link/ether b8:27:eb:ba:51:4e brd ff:ff:ff:ff:ff:ff
    inet 192.168.1.53/24 brd 192.168.1.255 scope global wlan0
       valid_lft forever preferred_lft forever
    inet6 fe80::88a6:314a:4819:9fd1/64 scope link 
       valid_lft forever preferred_lft forever
5: tun0: <POINTOPOINT,MULTICAST,NOARP,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UNKNOWN group default qlen 100
    link/none 
    inet 10.8.0.5/20 brd 10.8.15.255 scope global tun0
       valid_lft forever preferred_lft forever
    inet6 fe80::5c34:f7d7:fb58:c10c/64 scope link flags 800 
       valid_lft forever preferred_lft forever

And Output of

ip route

default via 192.168.1.1 dev wlan0  metric 303 
10.8.0.0/20 dev tun0  proto kernel  scope link  src 10.8.0.5 
10.10.10.0/24 via 10.8.0.1 dev tun0  metric 101 
10.10.10.0/24 dev eth0  proto kernel  scope link  src 10.10.10.10  metric 202 
172.27.224.0/20 via 10.8.0.1 dev tun0  metric 101 
192.168.1.0/24 dev wlan0  proto kernel  scope link  src 192.168.1.53  metric 303 
192.168.1.1 via 10.8.0.1 dev tun0  metric 101 
192.168.31.0/24 via 10.8.0.1 dev tun0  metric 101 

Answer 1

You wrote that "Device B and Device C are OpenVPN clients connected to same OpenVPN access server". That is important because only the server can route traffic between the clients that are connected to it. So configure the server to forward ip packets on its (pseudo) interfaces and manage its routing table so traffic goes where you want. As far as I know the OpenVPN server has an option to set that clients can talk to each other.