Windows Server 2012 R2 ships with the ability to add .NET Framework 3.5 (which includes 2.0 and 3.0) as a Windows feature. Because Server 2012 R2 typically has its installation media trimmed and component store (WinSxS) handling changed from older Windows versions, administrators often encounter the file Microsoft-Windows-NetFx3-OnDemand-Package.cab when installing .NET 3.5 “Features on Demand.” This essay examines what that CAB is, why it matters, common deployment scenarios, security and integrity concerns, and practical guidance for administrators.