When installing Roles or Features on Windows Server 2012 R2, you get this message:
Do you need to specify an alternate source path? One or more installation selections are missing source files on the destination server. The server will try to get missing source files from Windows Update, or from a location that is specified by Group Policy. You can also click the “Specify an alternate source path” link on this page to provide a valid location for the source files.
The Do you need to specify an alternate source path message is just a warning to let you know that some of the roles or features you have selected do not have source files (installation files) on the server.
To fix this, do nothing. The source files should automatically be downloaded from Microsoft, over the internet connection. If the server doesn’t have an internet connection or the connection is blocked by a firewall, you can specify to install these files from the Windows Server 2012 R2 installation media.
Typically this happens with the installation of .NET 3.5. To install .NET 3.5 from installation media, use the following DISM command: