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 to provide a valid location for the source files.
Above error message is caused because of Windows 2012 missing files. Windows 2012 removes all installation files if that features are not in use.
To fix Do you need to specify an alternate source path? error follow below steps,
1. Click Specify an alternate source path as shown in above image to specify the source path of installation files i.e. Windows 2012 CD/ISO image.
Click on Install to continue with your feature installation after specifying Source Path.
OR you can use below command to install Windows features,
dism.exe /online /enable-feature /all /featurename:NetFX3 /Source:D:\sources\sxs /LimitAccess