Sending value to the PLC

[rus25]

On the RUT956, I am currently reading Modbus values from an I/O device connected to the RUT901. I want to send these values to the PLC. I can already read values from the PLC.

The RUT956 and RUT901 are connected via the RMS VPN Hub.

• RUT956 IP: 192.168.1.1
• RUT901 IP: 192.168.1.2
• PLC IP: 192.168.1.3 (connected to RUT956)
• Modbus I/O device IP: 192.168.1.4 (connected to RUT901)

How can I achieve this? Or could the PLC perhaps access the Modbus I/O device directly?

[anon65719490]

Hello,

From your described configuration, the first thing that stands out is that both routers, RUT956 and RUT901, are operating within the same 192.168.1.0/24 subnet. In most cases, for reliable Modbus TCP communication (or any routed traffic between different network segments over a VPN), it’s recommended that each router’s LAN operate on a different subnet, e.g., RUT956 LAN: 192.168.1.0/24, RUT901 LAN: 192.168.2.0/24.

Then, you would add appropriate static routes to both routers so that traffic for the PLC and the I/O device can be properly routed through the VPN:

• route to 192.168.2.0/24 or I/O device LAN IP via the RUT956 (gateway)
• route to 192.168.1.0/24 or PLC LAN IP via the RUT901 (gateway)
• enabling Masquerading option on both routers LAN zone (Network → Firewall → Zones)

If your PLC supports acting as a Modbus TCP client and the I/O device is reachable (i.e., you can successfully ping the I/O device’s IP from the PLC), then direct PLC-to-I/O communication should be achievable across the VPN link once the subnets and routes are correctly configured.

Feel free to reach out if you have further questions or need assistance with the setup.

Best regards,