Install Net 3.5 Framework on Windows Server 2012 without DVD

To install the .net 3.5 on server 2012 without the disk (or disk image):

1. Ensure that the server is NOT looking at a WSUS server for updates (must be looking at Windows Update for this to work)
2. Ensure that any proxy/firewall will allow the connection from the server in question to the Windows update service

3. From a command line run:

   dism.exe /online /enable-feature /featurename:NetFX3 /all
   

   The elimination of the source switch is done on purpose as this will force the server to look within its own SxS folder, not find the needed files, and then go to Windows Update for the files (hence step 1 where it is not pointing to a WSUS server).

You can configure server to use Windows Update as a source for for optional components installation. And then install .NET 3.5 through the Add Roles and Features Wizard.

You can configure server by registry:

[HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\Policies\Servicing]
"RepairContentServerSource"=DWORD(2)

or by Group Policy:

Computer Configuration -> Administrative Templates -> System
"Specify settings for optional component installation and component repair"

found here:

https://www.404techsupport.com/2012/11/server-2012-you-must-use-the-role-management-tool-to-install-or-configure-microsoft-net/

https://msdn.microsoft.com/en-us/library/windows/desktop/hh848079(v=vs.85).aspx?ppud=4&tduid=(ad1620201cdb131ba52a8e05b8ffef0c)(256380)(2459594)(TnL5HPStwNw-mxEPD8HDp4sXn1EnYFo1cA)()