By default, .NET Framework 3.5 is not installed on Server 2019 and also the sources are not getting installed. If you open Roles and Features and select the feature and start the installation you are likely to get an error message (0x800F0950). The same is true when you download it from the Microsoft content server and try to install it by dism or Enable-WindowsOptionalFeature.

You have to take the sources from the sources\sxs folder of the Server 2019 iso file. If you have the installation DVD still inserted (which is usually the case if you set up a virtual machine) you can enter the path (probably d:\sources\sxs) on the Confirmation page of the Add-Roles-And-Features-wizard by selecting Specify an alternate source path.
Alternatively, mount the iso by double-clicking it (Win8 or later), copy the 2 microsoft-windows-netfx3… cab files in the folder sources\sxs and paste them to your server. Afterwards, you can call
dism /online /Add-Package /PackagePath:[sourcepath]\microsoft-windows-netfx3-ondemand-package~31bf3856ad364e35~amd64~~.cab.


was struggling with this, trying to install net 2.5 on server 2019. very helpful thanks
typo, .net 3.5
Worked!! Thanks you so much
or you can do the select alternative source and give the parth.
Worked for me – thanks!
Thank you , works very well
Worked!! Thanks you.
Thank you so much for taking the time to write this. V. helpful.
thumbs up, still works like a charm
awesome – thanks!
Thanks for pointing out that you need to use the 2 files from the folder sources\sxs on an ISO with server 2019 on, and not to use the ordinary installationfiles for .net 3.5 you can download from Microsoft.
Strange they are not copied to the sxs folder on the server during the server’s installation.
Quickest solution to install.
Merci, avec le CD W2019 ça fonctionne aussi
it is worked
thanks
This is helpful and working! Thank you for sharing!
Its worked! thank you
Thanks a lot! it works great!
worked like charm 🙂
Worked like a charm.. Thanks a lot.
I mounted my disk image but in this folder specifically I can’t find these cab files…anyone with the same problem?
You are looking at [drive]\sources\sxs of the installation iso, right? The file should be in there.
Thanks a lot! It worked.
Thanks for this post! The solution worked as directed.
Thanks! Worked as expected. I used the copy files from ISO to another server and install via dism method.
Thank you! 🙂
I been struggling. Thank you for your help.
Worked as expected. Thank you sir!
thanks suggestion worked ..!
Thanks for this help, it works perfectly
thank you very much worked for me
I don’t have a disc or a iso how can I get the iso downloaded from the web? Or these two files rather.
I assume that you can take the sources from the eval center: https://www.microsoft.com/de-de/evalcenter/evaluate-windows-server-2019
This worked perfectly. Thanks.
thanks a lot