Hello,
Your Robustel device must have a LAN network. If it indeed does not - than you cannot establish VPN from it, since VPN in general in meant to connect to remote networks together. If there is no network - VPN would not work. However, since your Robustel has VPN configuration, it must have LAN network as well, but it simply might be hidden from basic menus.
From your screenshots I can see that there is conflicting configuration:
- Your Robustel device is configured to listen to its own WAN IP address
- MTU is set to 1500. Depending on the situation, that might cause communication issues. For testing purposes try to use lower MTU, e.g. 1400
- On RUT240 you have specified that remote network is same, are remote host network. Such configuration would indeed cause networking issues on your RUT240 device.
My suggestion in this situation: remove Robustel as a variable and for your first OpenVPN tunnel try to use two Teltonika device. That would have an advantage, since we have detailed configuration example for our devices, which you would be able to follow and avoid configuration errors. After making few successful VPN connections using instructions you would have general idea what settings are most important and what values they suppose to have. Then you would be able to experiment using any other equipment, which might not have instructions. OpenVPN configuration example how to create tunnel between two Teltonika devices can be found here:
https://wiki.teltonika-networks.com/view/OpenVPN_configuration_examples
Meanwhile, if you would like to find out more information about OpenVPN in general, here you can find very good official OpenVPN community article, which explains all OpenVPN details, from configuration nuances to troubleshooting steps:
https://openvpn.net/community-resources/how-to/