you have just installed a fresh new Windows Server 2012R2 on premise or in Azure and you need to install .Net Framework 3.5 Features

But it fails with an error 0x800f081f

a quick search says you need this command to do this well eh why ? but any way it is on the web so it must be right .

dism.exe /Online /Enable-Feature /FeatureName:NetFx3 /All /LimitAccess /Source:E:\sources\sxs <> Will not Work

But why everybody says thanks! let me that you to the real problem. Reminder this is for all Servers even in Azure !

We checked the .Net Framework 3.5 Features and failed

Next attempt Give the Source to the installation. not very handy in Azure first download a ISO then mount this to the OS.

But it is on the Web so it must be true and the installation says he I need a Source I do not have these files and the OS is not lying or does it ?

So we put in the Source and give it a try.

Same error and with the source, maybe my source is not right , yeh right.

Test tis one more time form the Command

Then there is this line, this should work eh yes is did not.

dism.exe /Online /Enable-Feature /FeatureName:NetFx3 /All /LimitAccess /Source:E:\sources\sxs

See it did not work, I told you so in the first line So what is really going on in this system.

The Real fix for installing .NET Framework 3.5 Feature and Error 0x800f081f

If you open a PowerShell window and query the roles and features Get-WindowsFeature take a look at .NET Framework 3.5.

In the last column the Install state is different, it says Removed ?

Removed means that you can install the feature but the source files for that are not available for this OS (not always)
Installed means that the role or feature is already enabled and in use
Available means that you can install the feature and the source files are on the machine and the OS can use them

But Removed, If the @Azure Team has removed this feature could this be the problem ?

Let me check if there are Updates for my system.

What there is an update for me and I do not have the .NET 3.5 Framework features installed.

then there must be an update there for me that is nagging me. Let me search the updates for .NET 3.5 Framework and compare them to the Installed updates.

KB2966828 http://support2.microsoft.com/kb/2966828

This is an .NET 3.5 Framework update ad must be installed when the .NET 3.5 Framework was installed and patched