How to send CTRL + ALT + DEL to a Remote Desktop session running within a Remote Desktop session

While connected to a customer’s server via RDP yesterday morning, I needed to send CTRL + ALT + DEL to another machine to which I was connected via a different RDP session running on the first server. It’s easy enough to do that over one level of RDP—you just press CTRL + ALT + END—but how was I supposed to send it to an RDP session running within another RDP session?

The solution provided by user Dave in a Server Fault thread was to use the first server’s On-Screen Keyboard. I went to the Windows menu, searched for that, and was able to send the keystrokes right over. Problem solved!