Using OPC via DCOM with Microsoft Windows XP Service Pack 2

The major goal of Windows XP Service Pack 2 is to reduce common available scenarios for malicious attack on Windows XP. The Service Pack will reduce the effect of most common attacks in four ways:

  1. Improvement in shielding Windows XP from the network
    1. RPC and DCOM communication enhancements
    2. Enhancements to the internal Windows firewall
  2. Enhanced memory protection
  3. Safer handling of e-mail
  4. Internet Explorer security enhancements.

Most OPC Clients and Servers use DCOM to communicate over a network and thus will be impacted due to the changes in Service Pack 2. When Service Pack 2 is installed with its default configuration settings, OPC communication via DCOM will cease to work. This paper describes the settings necessary to restore OPC communication when using XP Service Pack 2 (SP2).

SP2 includes many changes and security enhancements, two of which directly impact OPC via DCOM. First new DCOM limit settings have been added. Secondly the software firewall included with XP has been greatly enhanced and is turned on by default.

Since the callback mechanism used by OPC essentially turns the OPC Client into a DCOM Server and the OPC Server into a DCOM Client, the instructions provided here must be followed on all nodes that contain either OPC Servers or OPC Clients.

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