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You can make iron farms(and the others), but there is no way to be afk and not get kicked for being afk.
The server will kick you even if you try to make an anti-afk machine. I tried with portal guns, so I could go eat my dinner but I came back and I was kicked.
Seems that the vanilla anti afk system is pretty smart. 
Seems that the vanilla anti afk system is pretty smart.
Well then the server I had was TOO smart 
