OPC Server Computer Recommended Settings - Step 3
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This section covers the DCOM settings for the OPC server computer that are specific to the application OPCEnum that every OPC server should install.  You may skip this step depending on how your application works. If your OPC client allows your users to browse for OPC servers that are on the machine where your OPC servers are installed and then pick from a list, then you will need to complete this step. Also, if you will be running the OPC Data ActiveX demo programs (i.e. browse demo) that allow for server browsing, then you will need to complete this step.  If none of these apply, you are done with the computer where the OPC servers reside and may move on to configuration of the OPC client computer.  You should already have the DCOM Config Utility running and go to the Applications tab. Go to the Applications tab in DCOM Config and browse until you find the listing OPCEnum and highlight it and either double click on it or click the Properties button to enter the server specific settings. Note - the settings we are about to make are the same as the recommended settings for most OPC servers - we have found that if you change one of these, you need to change the other if you allow clients to browse for available servers in your client application. OPCEnum Properties: General Tab On the General Tab, we recommend that you leave the Authentication level to Default. This will mean that this server will use the method of determining who will be allowed access that was setup on the Default Properties tab in the DCOM Config utility. We do NOT recommend that you change this setting unless you know what you are doing or are directed to by one of our support engineers. OPCEnum Properties: Location Tab Make sure that the Run application on this computer is the ONLY check box checked. The Run application on the computer where the data is located check box should NOT be checked, and the Run application on the following computer should NOT be checked. OPCEnum Properties: Security Tab 1. We suggest you select "Use Default Access Permissions", which will mean users/groups shown under Default Access Permissions on the Default Security tab in the DCOM Config utility will have access to connect to OPCEnum and browse for available servers.  Understand that if you select "custom" and put no groups/users into the list, then no client, local or remote, will be able to connect.  So if you choose to use the custom permissions to override the defaults, know which users/groups you wish to grant permission to. 2. We also suggest that you use the Default Launch Permissions, which will mean users/groups shown under Default Launch Permissions on the Default Security tab in the DCOM Config utility will have access to launch OPCEnum and browse for available servers.  The same rules apply about using custom launch permissions here as they do for custom access permissions - use with care and know what you are setting.  If you use custom and set nothing, no users will be able to launch your OPC server. 3. When properly installed by an OPC server install set OPCEnum sets up Custom Configuration Permissions by default - it is our recommendation that you do not modify these unless instructed by the OPC server documentation or the OPC server vendor's support staff.  OPCEnum Properties: Identity Tab On the Identity tab, you specify under what user account you want the OPCEnum to run under. This is probably one of the MOST important settings for OPCEnum in some cases. The answer is very dependent on HOW you will be using your system. 1. If you will NOT have anyone logged onto the machine where the OPC server and OPCEnum are running, then do NOT use the Interactive user. The reason is that if you did, and a remote client tried to launch the server, and on one was logged in on the OPC server computer, there would be no "interactive user" logged in to start the OPCEnum process under, thus you would not be able to get a list of available servers on this machine. In this case we recommend that run OPCEnum as a named user. 2. If a user will always be logged in on the machine where the OPC server is running, then you may use the Interactive User because that means there will be an "interactive user" under which to run the OPCEnum process. 3. We do NOT recommend using the Launching user as this will result in multiple copies of OPCEnum being started when multiple OPC clients connect. This does not cause the same harm as letting multiple copies of an OPC server launch though. OPCEnum Properties: Endpoints Tab - No changes required on this tab. You may now move on to configuring the OPC Client Computer DCOM settings.

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