When you are Offline and not connected to Internet
If you open CMD.EXE with Administrative Privileges i.e. at elevated
level & run this DISM command dism /online /get-features you will
see that from the State that .NET Framework is not part of the Operating System.
So the first thing you need to do is to copy the required package to local machine
before you run the command to install .NET Framework. To do that use Windows 8 ISO/DVD/USB Media.
You need to copy SXS folder to local machine located at D:\sources\sxs (In this case D: your drive
letter on which you have loaded Windows 8 Media)
Once completed, in order to install this feature you can run the following command
dism /online /enable-feature /featurename:NetFx3 /All /Source:C:\sxs /LimitAccess
and hit Enter
