A 6 month old isn't protective. He's trying out the big scary dog act because he's going through his second fear period.
You need to make everything happy and fun now. Enlist people to come over, hand them a bag of treats or toys to give to your puppy. Keep him on his leash and when he accepts a person (because you said to), he's the best dog in the whole wide world! If he barks and acts like a lunatic, shame and crate for the duration of the visit.
Venus of Crooked Creek 1/26/13
Otto von Hena-C 05/23/08
Morgan Donnermond 08/04/01 to 9/28/12 Long Live the Queen!
I have duct tape and I am not afraid to use it.