Technical questions, some very trivial (arp, traceroute, rtt, ..). On face to face interviews, it's sometimes related to social stuff (tell me when you didn't agree with your boss, with your colleagues, what did you do ...), and sometimes to technical questions (bgp, ospf, tcp, ...). Here it depends on how much you know about them, and the experience of your interviewer. I could have done many questions based on my experience that would have probably put them in trouble ... it is always like this. In any case, if you are not smart, you will probably not pass it.