I am trying to install .NET 3.5 on a client's Windows Server 2025 - where can I find the Features on Demand for 2025

Karl Pozmann 20 Reputation points
2026-09-01T20:00:03.4766667+00:00

Downloading failed and Gemini has recommended getting the Features on Demand ISO but not having any luck finding it. Any help would be appreciated.

Developer technologies | .NET | Other
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  1. Tony Thach (WICLOUD CORPORATION) 845 Reputation points Microsoft External Staff Moderator
    2026-09-02T02:19:29.2933333+00:00

    Hi  @Karl Pozmann , and thanks for posting your question. 

    The Server Core Application Compatibility Features on Demand ISO is not required just to install .NET Framework 3.5. That ISO provides additional compatibility tools for Server Core. For .NET Framework 3.5, the usual offline source is the Sources\SxS folder from matching Windows Server 2025 installation media.

    Mount a Windows Server 2025 ISO that matches the installed server’s version and language, note its drive letter, and run the following command in an elevated PowerShell window:

    Install-WindowsFeature NET-Framework-Core -Source D:\Sources\SxS

    Replace D: with the drive letter of the mounted ISO. You can confirm the installation with:

    Get-WindowsFeature NET-Framework-Core

    The install state should show Installed.

    If Windows continues trying Windows Update or WSUS instead of using the ISO, try DISM and restrict it to the local source:

    DISM /Online /Enable-Feature /FeatureName:NetFx3 /All /Source:D:\Sources\SxS /LimitAccess

    If you specifically need the Windows Server 2025 FoD media

    Microsoft provides a combined Languages and Optional Features ISO for Windows Server 2025 through the official Windows Server 2025 Evaluation Center. For licensed production media, check the Microsoft 365 admin center or the licensing portal associated with the customer’s agreement.

    The separate Server Core Application Compatibility FoD package is intended to add compatibility components to Server Core, so it should not normally be required for installing .NET Framework 3.5.

    If the installation still fails

    The exact error code can help identify the cause:

    1. 0x800F081F: The required source files could not be found.
    2. 0x800F0906: Windows could not download the required files.
    3. 0x800F0907: A Group Policy setting may be preventing the download.

    If the server is managed through WSUS, also review this policy:

    Computer Configuration
  > Administrative Templates
  > System
  > Specify settings for optional component installation and component repair

    Depending on your organization’s policy, you can either configure a valid alternate source path or allow the server to contact Windows Update directly for optional component and repair content.

    If it still does not install, please share the exact error code, the output of winver, whether the server uses WSUS, and the relevant entries from:

    C:\Windows\Logs\DISM\dism.log
C:\Windows\Logs\CBS\CBS.log

    Please remove hostnames, domain details, credentials, and any business-sensitive information before posting the logs.

    I will be happy to help review the error and determine whether the problem is caused by the installation source, a Group Policy setting, WSUS configuration, or a Windows servicing issue.

    If this instruction is applicable to your situation, I would greatly appreciate it if you could follow the instruction here so others experiencing similar behavior can benefit from it as well.  

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  2. AI answer

    2026-09-01T20:00:15.8466667+00:00

    For Windows Server 2025, the Features on Demand ISO is listed in the Server Core Application Compatibility documentation under Windows Server 2025.

    Use this download entry:

    If the goal is specifically to install .NET Framework 3.5 on Windows Server, these points apply:

    1. .NET Framework 3.5 files aren’t stored locally by default on Windows Server 2012 and later.
    2. Installation normally tries Windows Update first unless an alternate source is configured.
    3. If downloading failed, install from a matching source for the same Windows Server version.
    4. On Windows Server, .NET 3.5 can be enabled through Add Roles and Features Wizard by selecting .NET Framework 3.5 Features.
    5. If using PowerShell with installation media, the documented example is: 
         Install-WindowsFeature NET-Framework-Core -Source D:\Sources\SxS
      Replace D: with the drive letter for the mounted media or source location.

    Important: use source files that match the exact Windows operating system version. Using files from a different Windows version can fail or leave the system unsupported.

    AI-generated content may be incorrect. Read our transparency notes for more information.

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