M221 OpenVPN Not Working

[Simon_G]

Hello all,

I need to have a M221 read the values from another M221 that it located remotely. The application is not safety critical, and I can deal with gaps in comms of up to 15 seconds before the local M221 enters a 'comms failed' state and switches off the stuff is is controlling.

 4G would be ideal (hard wiring is not an option). To test I have x2 M221, each connected to a Teletonika TRB140. Teteonika RMS is then used to configure a VPN between the two (via OpenVPN).

The gateways can ping the local M221, as well as the other M221 (over the 4G VPN link). With the VPN client on my PC I can ping each M221.

When I use a direct ethernet cable between the two M221s, they can read the data in each other via the IO Scanner.

I cannot get it to work over the VPN link. I have tried playing with the time out periods and the cycle trigger times. 

Any ideas if this is actually possible, and what could be going wrong?

Thanks in advance.

[Trinxs1]

I am not familiar with Teltonika however it would help if you were able to capture the modbus communications from one another using wireshark.  This hopefully will give you a better idea of what is going on.

[Bastian_Schmitz]

You could try if you could send with a third party modbustool like Modbus Poll via VPN from one to the other site. this imitate the native connection. And you could check if Port 502 is open for this connection. This is the standard port for Modbus TCP