I suppose if you're a network engineer http/udp/tcp is necessary to know maybe off hand but not really, http isn't even in the same network layer so I'd find it strange to even ask about the 'difference'. UDP and TCP differences are more or less a well known question but even then I've had some ask the question expecting the most basic of differences and others with the minutiae.

btree index is also something that can be learned conceptually in about 10 minutes.

It is far more important for me to see that someone can explain a project that they've worked on in the past with enough details to demonstrate sufficient technical knowledge than a litmus test based on somewhat arbitrary facts. 'don't know what lsof is? Not hired, I don't want someone who can't use shell'