A. ConfigMgr.manifest.cab contains details of updates available for the SCCM installation. It's not available as a standard download from Microsoft. Instead, you need to run a specific command on a machine that has Internet connectivity (it doesn't have to be a server—I used a Windows 7 desktop). The command downloads all the updates and can place them in a folder, which you can then direct the setup process to use for updates during the SCCM installation.
Navigate to SMSSETUP\BIN\I386 folder on your SCCM media from a command line and run the command