Configuring IIS to Use the Correct Version of the .NET Framework

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Applies To: Windows Server 2003, Windows Server 2003 with SP1

If you have migrated ASP.NET applications that were developed with version 1.0 of the .NET Framework, you might have to install version 1.0 of the .NET Framework on the target server to ensure that your applications continue to function properly. After migration, version 1.1 of the .NET Framework is installed on the target server and the applications are configured to use version 1.1 of the .NET Framework. After installing version 1.0 of the .NET Framework, both version 1.0 and 1.1 of the .NET Framework are installed on the target server. This is referred to as side-by-side support.

Running versions 1.0 and 1.1 of the .NET Framework side-by-side is only supported when IIS is configured to run in IIS 5.0 isolation mode. If you have already configured IIS to run in worker process isolation mode, then you can only use version 1.1 of the .NET Framework on the target server. In most cases, ASP.NET applications function correctly with version 1.1 of the .NET Framework. For more information about possible application incompatibilities when migrating from version 1.0 to version 1.1 of the .NET Framework, see Determining Application Compatibility with the .NET Framework earlier in this section. When your ASP.NET application is incompatible with version 1.1 of the .NET Framework, configure the application to use version 1.0 of the .NET Framework and configure IIS to run in IIS 5.0 isolation mode.

You can configure each ASP.NET application to use a specific version of the .NET Framework by registering a script map in IIS for the application. A script map associates a file name extension and HTTP verb with the appropriate ISAPI for script handling. For example, when IIS receives a request for a .aspx file, the script map for the corresponding application directs IIS to forward the requested file to the appropriate version of the ASP.NET ISAPI for processing.

The script map for each ASP.NET application can be applied directly to an application, or inherited from a parent application. However, ASP.NET supports only one version of the .NET Framework for each application pool. For more information about how to configure the script map for an ASP.NET application, see Configure an ASP.NET Application for ASP.NET.