If you are trying to add certain roles/features in Windows Server 2012 you will see the below error.

“Do you need to specify an alternate source path? One or more installation selections are missing source files on the destination server. The server will try to get missing source files from Windows Update, or from a location that is specified by Group Policy. You can also click the “Specify an alternate source path” link to provide a valid location for the source files.”

 It’s a security feature called “Features on Demand” added on Server 2012. With this feature, Microsoft is trying to reduce the security footprint on Windows servers by not keeping the binary files on every servers.

Because Microsoft finds that 90% of the updates which are currently installed on any windows server is for the features which are not even used on that particular server. By having these removed by default, Microsoft says that every server is saved from 90% of surface attack.

If you are seeing the above error you have two options to continue the installation further.

 1) Specify the installation path on GUI by clicking on the “Specify an alternative source path”

Then enter the path on this window.

Path should something like this D:\sources\sxs

 2) Specify the path on the command line installation.

Dism /online /enable-feature /featurename:NetFx3 /All /Source:x:\sources\sxs /LimitAccess

Were X should be the drive letter

The above mentioned command line is for reference only. The alternate path can be specified with any of your desired commands.