Linux – OpenVPN and port forwarding

I have an issue with my Linux-based server regarding VPN and port forwarding. I am also a beginner is this area, so forgive me for any mistake.

First, let me describe you the infrastructure. I have a Linux VPS server (S1) with openvpn properly configured, and a machine with Linux (C1) also with openvpn properly configured. THe are connected using port number 1194. This is basically the scheme:

    S1
    [ip: X.X.X.221]
    [tun0 ip: 10.8.0.1]

    C1
    [ip: Y.Y.Y.19]
    [tun0 ip: 10.8.0.6]

When I say it is all properly configured is because I can successfully ping 10.8.0.1 from C1.

Now, it comes the problem…
I have a service P1 running on port 1800 in S1, and a client for that service in C1. I can successfully give the IP address X.X.X.221:1800 to the client in C1, but I want the client to acess P1 via VPN connection. Is that a way to do it?

At first I thought this was simply a port forwarding problem, and all I needed to do was to forward every request from port 1194 to port 1800, and I found this command to do it (btw, venet0 is my interface):

    iptables -t nat -A PREROUTING -i venet0 -p udp --dport 1194 -j REDIRECT --to-port 1800

But this won't work.

Any help? Thanks 🙂

EDIT1:

Result of issuing netstat -rn and 10.8.0.6 in S1:

    Kernel IP routing table
    Destination     Gateway         Genmask         Flags   MSS Window  irtt Iface
    10.8.0.2        0.0.0.0         255.255.255.255 UH        0 0          0 tun0
    10.8.0.0        10.8.0.2        255.255.255.0   UG        0 0          0 tun0
    0.0.0.0         0.0.0.0         0.0.0.0         U         0 0          0 venet0

    traceroute to 10.8.0.6 (10.8.0.6), 30 hops max, 60 byte packets
     1  10.8.0.6 (10.8.0.6)  116.769 ms  119.000 ms  120.618 ms

Result of issuing netstat -rn and traceroute 10.8.0.1 in C1:

    Kernel IP routing table
    Destination     Gateway         Genmask         Flags   MSS Window  irtt Iface
    0.0.0.0         192.168.1.254   0.0.0.0         UG        0 0          0 eth0
    10.8.0.1        10.8.0.5        255.255.255.255 UGH       0 0          0 tun0
    10.8.0.5        0.0.0.0         255.255.255.255 UH        0 0          0 tun0
    192.168.1.0     0.0.0.0         255.255.255.0   U         0 0          0 eth0

    traceroute to 10.8.0.1 (10.8.0.1), 30 hops max, 38 byte packets
     1  10.8.0.1 (10.8.0.1)  83.825 ms  83.639 ms  86.877 ms

EDIT 2:

Configuration file for S1 (I believe what starts with a ; is not considered):

    ;local a.b.c.d
    port 1194
    proto udp
    dev tun
    ;dev-node MyTap
    ca ca.crt
    cert server.crt
    key server.key  # This file should be kept secret
    dh dh2048.pem
    server 10.8.0.0 255.255.255.0
    ifconfig-pool-persist ipp.txt
    ;server-bridge 10.8.0.4 255.255.255.0 10.8.0.50 10.8.0.100
    ;push "route 192.168.10.0 255.255.255.0"
    ;push "route 192.168.20.0 255.255.255.0"
    ;client-config-dir ccd
    ;route 192.168.40.128 255.255.255.248
    ;client-config-dir ccd
    ;route 10.9.0.0 255.255.255.252
    ;learn-address ./script
    push "dhcp-option DNS 8.8.8.8"
    push "dhcp-option WINS 8.8.4.4"
    ;client-to-client
    ;duplicate-cn
    keepalive 10 120
    ;tls-auth ta.key 0 # This file is secret
    ;cipher BF-CBC        # Blowfish (default)
    ;cipher AES-128-CBC   # AES
    ;cipher DES-EDE3-CBC  # Triple-DES
    comp-lzo
    ;max-clients 300
    user root
    group root
    persist-key
    persist-tun
    status openvpn-status.log
    ;log         openvpn.log
    ;log-append  openvpn.log
    verb 3
    ;mute 20

Configuration file for C1

    client
    remote 176.9.192.221 1194
    ca ca.crt
    cert client.crt
    key client.key
    cipher BF-CBC
    comp-lzo
    dev tun
    proto udp
    nobind
    persist-key
    persist-tun
    user root
    group root