Restore Windows Security

Once the OPC client/server communication has been established, it is important to secure the computers again by turning on the Windows Firewall. This will block all unauthorized network traffic. It is also necessary to provide exceptions on two main levels:

  1. Application level. Specify which applications are able to respond to unsolicited requests:
  • Add OPCEnum and [company name].OPC.Server.DA to the allowed applications list.
  1. Port-and-protocol level. Specify that the firewall must allow or deny traffic on a specific port for either TCP or UDP traffic:
  • Open 135 port with TCP protocol.
    This port is commonly used for allowing the clients to discover and use a DCOM service (for example, OPCEnum).

Apart from the server computer, you must also set the firewall on the client computer so that callbacks can be received. In this case, you must add the OPC clients to the allowed applications list.