.NET 3.5 Installation failed on Windows Server 2012 R2

.NET 3.5 Installation failed on Windows Server 2012 R2 because the server configured to use WSUS instead of Windows update service.

Try the below steps to install .NET3.5
1. Goto group policy (run->gpedit.msc)
2. Navigate Computer Configuration ->Administrative Templates ->System
3. Enable Specify settings for optional component installation and computer repair.
4. Select "Conatct Windows Update directly to download repair content instead of WSUS.
5. Now try the .Net 3.5 install from Add Roles and Features Wizard.

Ref : https://support.microsoft.com/en-us/kb/2734782