I always start off with nice easy questions, like what is a LUN? This helps the person settle down and get past nerves etc. It is good to keep them over a broad range of topics to get an idea of the scope of knowledge. I always like the physical cable question. What can you tell me about that. It can show they have a sense of humor and weather of not they know anything about cables. If they can not tell you what a (patch lead / crossover cable) is, they are missing very basic skills so start to question how hands on they are.
The network diagram with a bad default gateway is also good. Shows problem solving and they understand basic IP.