Quite a number of applications in Windows Server 2016 / Windows 10 require .Net Framework 3.5, in spite of .NET Framework 4.6 is installed by default. For example, I was not able to install and run SQL Management Studio without .Net 3.5.
Let’s consider how to install .Net Framework 3.5 in Windows Server 2016
When trying to install .Net 3.5 using Server Manager (Add Roles and Features -> Features -> Net Framework 3.5 Features), the installation stops with the error 0x800f081f (The source files could not be found).
Although, .Net Framework 3.5 is present in the list of Windows Server 2016 components, its binary files are missing in Windows component Store (Features on Demand concept). So to install it, you will need Windows Server 2016 distribution in an ISO file or unpacked in the network share. Mount the ISO image containing the distribution as a virtual drive (e. g., driveD:). You can install the component using the GUI or PowerShell.
How to Install .Net Framework 3.5 Using Server Manager Graphic Console
You can install .Net 3.5 using Server Manager graphic console. To do it, select the component as earlier, but prior to clicking Install, click a small link at the bottom of the wizard — Specify an alternate source path.
In this window you have to specify the path to the SxS folder of your Windows Server 2016 distribution image. If you have mounted the distribution as a virtual disk, the path may look like D:\sources\sxs. It can also be the network share, where you copied the distribution (e. g., \\server1\distr\ws2016\sources\sxs). Then click OK.
Just run the installation.
How to Install .Net Framework 3.5 Using PowerShell
It is much easier to install Net Framework 3.5 Features using PowerShell started with the administration privileges. Just run the command:
Dism.exe /online /enable-feature /featurename:NetFX3 /All /Source:D:\sources\sxs /LimitAccess
Where D:\ is the drive with Windows Server 2016 source files.
You can also install the component using this command:
Add-WindowsFeature NET-Framework-Core -Source d:\sources\sxs
After the component installation is completed, the server does not need to be rebooted.