/featurename:NetFX3 : Specifies that you want to install .NET 3.5. /Source : Points to the exact location of the .cab file.
/online : Tells the tool to make changes to the operating system currently running. Download Microsoft-windows-netfx3-ondemand-package.cab
Dism /online /enable-feature /featurename:NetFX3 /All /Source:D:\sources\sxs /LimitAccess Use code with caution. /featurename:NetFX3 : Specifies that you want to install