Resolving Error Code 0x800f0818 During .NET Framework 3.5 Installation on Windows Server 2008 R2

To address the error code 0x800f0818 when installing .NET Framework 3.5 on Windows Server 2008 R2, use the following steps:

1. Verify .NET Framework 3.5 feature: Open Server Manager, navigate to Features, and check .NET Framework 3.5. Enable it if it is not already active and attempt the installation again.
2. Ensure installation source availability: Verify that your DVD or ISO file, which serves as the installation source, is readily accessible.
3. Update and restart server: Install any pending updates and perform a necessary restart to ensure all new configurations are set before proceeding with the installation.
4. Use DISM for installation: Launch Command Prompt as an administrator and execute:

      dism /online /enable-feature /featurename:NetFx3 /all /source::\sources\sxs /LimitAccess   

   Replace with the appropriate drive letter of your installation source.
5. Repair Windows installation: If other methods fail, consider using the installation media to repair your Windows Server 2008 R2. Boot from the media and select the repair option.