Microsoft-windows-netfx3-ondemand-package.cab -extra -

This is the preferred method for system administrators and is reliable for offline installations.

DISM /Online /Enable-Feature /FeatureName:NetFx3 /All /LimitAccess /Source:"D:\sources\sxs"

To understand the file, we must break down its naming convention:

This CAB file is the offline installer for .NET Framework 3.5. It is typically found on your original Windows installation media (ISO, USB drive) inside the sources\sxs folder. Microsoft-windows-netfx3-ondemand-package.cab -Extra

If you are an IT admin, developer, or power user, you need this CAB file for three primary reasons:

If you have mounted a Windows ISO file, the .NET 3.5 payload is not stored as a single .cab file on the root. Instead, it is located within the installation sources. The path usually looks like this: D:\sources\sxs\microsoft-windows-netfx3-ondemand-package.cab (Where D: is the drive letter of the mounted ISO) This is the preferred method for system administrators

Note that in the sxs (Side-by-Side) folder, there may be multiple cabinet files, but this specific one is the "parent" package that initiates the installation.

Meaning: Windows cannot find the source files. It is looking for the CAB, but your path is wrong, or the file is corrupted. PowerShell:

Solution with "-Extra" context: If your CAB is named ..._extra.cab, rename it to the exact canonical name: microsoft-windows-netfx3-ondemand-package.cab. Sometimes a download manager adds "extra" to the file extension (e.g., .cab.extra). Remove that.