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Why Windows Machine Names Are Case-Sensitive in RDP

I had the devil’s own time using the Remote Desktop Connection to get to one of my laptops this week. The machine name for that PC is T520 and it just wouldn’t “take” in the interface to the program (see screencap below). On a whim, I tried the string “t520” instead. And presto! I got a certificate warning page from RDP. That’s usual after each feature upgrade in Windows 10. It also led me to the explanation of why Windows machine names are case-sensitive in RDP. Let me explain…

I was stumped by RDP’s inability to see my T520 machine, until I tried the string “t520” instead. Who knew?

Why Windows Machine Names Are Case-Sensitive in RDP: It’s the Certificate!

The only thing I can figure is that the first time I connected to this machine, I used the lower-case version of the machine name instead of the upper-case version. Turns out that while machine names in Windows are completely case-insensitive, certficate names are case-sensitive. And because a certificate is used to negotiate the connection between the host and the client when using Remote Desktop, case matters. I’m just glad the T520 name only allows for two variations, or it might have taken me a while to figure out exactly what string I needed to use to get from Point A (my production desktop) to Point B (the T520 laptop).

Once I realized what was going on, I was able to find confirmation in a Microsoft TechNet blog post. It popped up  when I searched on “RDP machine name case-sensitive.” It’s entitled Remote Desktop Connection (RDP) – Certificate Warnings and is very much worth a read-through for those who, like me, work with RDP a lot. The following comment is where I confirmed my observations, though:

Here’s confirmation for you. Further experimentation with other local machine names vs. certificate labels provided further proof.
[Click image for full-sized view.]

Of course, in my case I didn’t get a warning. The connection simply wouldn’t form. But that was enough information for me to figure things out quickly. I’m just glad I stumbled into a test case where only two variations were possible! Now that’s some “dumb luck!”

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