This guide is aimed at solving the 0x800F0954 error you can get when trying to install .Net Framework 3.5 via PowerShell or through server manager.
You try to install .Net Framework 3.5 but the error 0x800F0954 is returned as shown below.
Mount the Operating System ISO
Run Powershell as Administrator then run the following command, updating the path to the sxs folder as per your environment
dism.exe /online /enable-feature /featurename:NetFX3 /All /Source:E:\sources\sxs /LimitAccess
.Net3 should now be installed
If option 1 does not work, try the following
Run regedit.exe, navigate to
Change UseWUServer to 0 then reboot the server and try installing again.
This will bypass any WSUS settings and talk directly to Microsoft (Please ensure you have internet connectivity for this)