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We have a modbus device running in a LAN:

port: 502

It is connected with a GSM router [RUT955] and no physical WAN connection. We would like to add some authentication to this connection. Therefore we would like to forward+tunnel this to our local Ubuntu server.

Let's say for example out ubuntu server has the following IP address:

What would be a solution to access the modbus device from with authentication?

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Could you draw a simple sketch of your network topology? Describe how everything is connected (IP,gateway, subnet) and describe what and from where you want to reach.

Hello Anonymouse,

I have a device connected to a RUT955.
The RUT955 has a 4G connection to the internet.
My Ubuntu Server is connected to the internet as well.
The Ubuntu Server has a fixed IP adress.
The RUT955 does not have a fixed IP adress.

I would like:

  1. Access to the Modbus TCP device from a client connected to the ubuntu server.
  2. Have some sort of authentication (client/server)

The RMS forwarding functionality would be perfect but it does not support raw TCP connections.

Ok, for this case you need to create one of VPN server in your ubuntu. Router support these: OpenVPN, IPsec, GRE Tunnel, PPTP, L2TP, STunnel, SSTP.

Some examples are here: