Installing .NET 3.5 on Windows10/8/Server 2012 With Powershell

Here's how to install .NET 3.5 (or another feature by subbing the feature name) on Windows 8/10 or Server 2012 from Powershell:

• Launch Powershell as Admin

Install .NET 3.5 using default sources (Windows Update or defined in group policy)

• 2012: Install-WindowsFeature –name NET-Framework-Core
• Win8/10: Enable-WindowsOptionalFeature –Online –FeatureName NetFx3 –All

Install .NET 3.5 using a network SxS share: 

• 2012: Install-WindowsFeature –name NET-Framework-Core -source \\server\share\source\sxs
• Win8/10:Enable-WindowsOptionalFeature –Online –FeatureName NetFx3 –All -LimitAccess -Source \\server\share\source\sxs
• On Windows 8, -all indicates that all parent features should be enabled as well and -LimitAccess prevents it from connecting to Windows Update. These options are not valid on Win 2012. 

Install .NET 3.5 using DVD-ROM 

• 2012: Install-WindowsFeature –name NET-Framework-Core -source j:\sources\sxs    (See note below)
• Win8:Enable-WindowsOptionalFeature –Online –FeatureName NetFx3 –All -LimitAccess -Source J:\sources\sxs

Make sure to run Windows Update after install if you're installing from a non-updated source!

Note: Depending on your configuration, on server 2012 you may need to use the install.wim on the install media and specify the index of the proper version of your install. To do so, execute:

Get-WindowsImage -ImagePath {OpticalDrive}:\sources\install.wim
This will display a list of images with associated indexes. Take note of the index of your install type.
Then, instead of the -source line above, use -source:wim:e:\sources\install.wim:X (where X is the number of the appropriate index. 

Update: Confirmed this works on Windows 10 as well!

WSUS 3.0 vs. 2012/Windows 8 Notes

As I posted earlier, server 2012 includes a new version of WSUS. There are a few gotchas associated with WSUS and Server 2012/Windows 8, especially as it pertains to using a previous version of WSUS. Here are some key points:

• Windows 8 and Server 2012 "clients" will NOT work with WSUS 3.0 SP2 or any version that isn't shipped with 2012 unless this update is installed BEFORE any clients connect to it. 
• If your Win8/2012 clients attempted to talk to an older WSUS server before patching or upgrading, you will need to perform the following before they will update again: 
• Net stop wuauserv
• rd /s %windir%\softwaredistribution\
• Net start wuauserv
• If your new WSUS 2012 server is downstream from an older WSUS server, it will have the same effect as if your clients were pulling directly from that older server. All WSUS servers between the clients and MSFT need to be newer or patched. 
• According to Microsoft, updates canNOT be scanned by an intermediary... i.e. HTTPS inspection must be turned off on content from Windows Update. 

Client errors may manifest themselves as "error 0x80246003". According to the WSUS error table that corresponds to an unrecognized hash. I haven't completed my research yet but I'm guessing that the new endpoints will only honor update packages from MSFT using a new, stronger hash to raise security in the aftermath of the Flame malware. 

Sources:

Microsoft: WSUS SP2 Patch

Microsoft: Discussion on this topic