“Do you want to specify an alternate source path? One or more installation selections are missing source files…”

To solve this, you can either:

1. Go to a command prompt and enter this:

dism /online /enable-feature /featurename:NetFX3 /all /Source:d:\sources\sxs /LimitAccess

Note: Source should be the Windows installation disc. In my case, this was located on D:

2. Go down to “Specify an alternate source path” and enter “d:\sources\sxs” as the path.

 

Note, if you need parent feature to be enabled first, use the /all option to automatically enable each parent feature.

In GUI

In the Confirm installation selections window, before click Install, click the Specify an alternate source path and provide the path as D:\Sources\sxs (where D is the drive letter where the Windows Server 2012 R2 media is mounted).