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Kepware Knowledge Base: Solution

Can I Use a VPN to Connect to an OPC DA Server on a Remote PC?

Last Update: 11/12/2018

No; however, Kepware provides an OPC UA Tunneling solution using the OPC UA Client Driver that allows the OPC DA client to establish a local connection to KEPServerEX V5 (which is both an OPC UA and OPC DA server). The OPC UA Client Driver then establishes a connection to KEPServerEX V5 on the remote PC. For more information, refer to OPC UA Tutorial.

Unfortunately, users cannot get requested data back to the client from the server when using OPC DA over a VPN connection. This is because OPC DA is designed using Microsoft's Component Object Model (COM) and uses Distributed COM (DCOM) for remote connectivity. When a connection is established to a remote server, and data requests are made by the client, the server will send callbacks (which are unsolicited messages from the server, like data change events) to the IP address that made the connection. When connected to a VPN, it will broker a local IP address on that network. When an OPC DA connection is established through a VPN, the brokered IP will be used not the IP of the PC with the OPC DA server. All callbacks to the client from the server will be sent to the brokered IP. The VPN does not have the ability to route the callback to the local OPC DA client.