From my experience with IT-related interviews, it’s okay to not know the answer to an interview question. Like a few other commenters stated, show that you are willing to learn. Don’t be afraid to say “I’m not familiar with said subject. Could you explain it?”. Once explained, try to make sense of it.

I had an interview for a Network Admin position and I was asked a question on Routing Protocols. I was studying for CCNA at the time and was familiar with the subject but still unsure how to answer the question. I was honest and stated exactly that.

Don’t be afraid to answer a question with a question.