Problem:
Remote connections using OPC Classic require the use of Microsoft Remote Procedure Call (RPC) technology, which uses dynamic ports. This makes firewall configuration difficult for hardware, since the application itself cannot be added by name.

Solution:
Although there is no direct solution, it is possible to limit the dynamic range used by RPC. This will make it more firewall-friendly. For more information, refer to Microsoft's How to configure RPC dynamic port allocation to work with firewalls.

Note: Users should be careful when limiting the dynamic port range to prevent port exhaustion. It is recommended that users consult with Information Technology before doing so.