From my (recent and meager) experience, it seems that any modern, well-configured access point will have encryption turned on, such that sending a deauth for this purpose requires a high degree of knowledge of the client's credentials and its secret knowledge. Furthermore, anyone who can spoof the target client, will surely have the skilz to send a simple deauth packet too. And anyone who can do that, can easily do the same for an open system.
As this is your first query here on the Monastery, I'm a little suspicious of your motives and the color of your hat =)
-QM
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Quantum Mechanics: The dreams stuff is made of
