.NET Framework 3.5 offline install for Win 10 1809 (OS build 17763.107) Enterprise LTSC

Obtain the licensed Windows 10 Enterprise LTSC 2019 (version 1809) ISO through your organization’s Volume Licensing downloads, then enable NetFx3 from that ISO’s sources\sxs folder with DISM.

Windows 10 does not support using the standalone .NET Framework 3.5 SP1 offline installer; offline installation requires the CAB payload from Windows installation media.^1^

1. Obtain the correct ISO

Windows 10 Enterprise LTSC 2019 corresponds to Windows 10 version 1809.^2^

If this installation is covered by Volume Licensing:

1. Sign in to the Microsoft 365 admin center using an account with the VL Administrator or Product download manager role for the relevant License ID.
2. Go to Billing → Your products → Volume licensing.
3. Select View downloads and keys.
4. Find Windows 10 Enterprise LTSC 2019, select the required language and architecture, and download the ISO.^3^
5. Transfer the ISO to the offline computer using approved removable media.

If you cannot see the download, contact your organization’s volume-licensing administrator. Access requires an applicable product license and the necessary VL role. The Media Creation Tool is intended for general Windows media and is not the appropriate source for Enterprise LTSC media.

Do not download an SxS folder or CAB file from an unrelated website or another Windows release. Microsoft warns that DISM may install a mismatched payload without blocking it, leaving Windows unsupported and unserviceable.^4^

2. Install .NET Framework 3.5 offline

1. Mount the ISO on the offline PC. Assume it appears as drive D:.
2. Confirm that this directory exists:

      D:\sources\sxs
   

3. Open Command Prompt as administrator.
4. Run:

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

   Replace D: with the actual mounted-media drive letter.
   • /All enables the required parent features.
   • /LimitAccess prevents attempts to contact Windows Update or WSUS.
   • /Source identifies the offline feature payload.^4^
5. Restart if requested.
6. Open Control Panel → Programs → Turn Windows features on or off and verify that .NET Framework 3.5 (includes .NET 2.0 and 3.0) is selected.

If matching LTSC media still fails

A machine whose servicing updates or installed language packs differ significantly from the source media can require a correspondingly serviced source. Microsoft documents that an alternative source which does not explicitly match installed hotfix or language-specific files can fail.^5^

In that case:

• Record the exact DISM error code and review %windir%\Logs\DISM\dism.log.
• Obtain updated LTSC 2019 media through the same licensing channel, or have the deployment administrator create correctly serviced media with NetFx3 included.
• Do not substitute media from Windows 10 1809 Home/Pro, Server 2019, LTSC 2021, or another language/architecture merely because it contains an SxS folder.

References

1. Install .NET Framework 3.5 on Windows 10 and Windows Server
2. Windows Enterprise LTSC
3. Download volume licensing products
4. Deploy .NET Framework 3.5 by using Deployment Image Servicing and Management (DISM)
5. Can't install the .NET Framework 3.5 without a public Internet environment on an OEM Windows installation