Exactly this. A "pass" on that question consists of mentioning HTTP, DNS, and (perhaps with some prompting about what protocols underlie HTTP) TCP. A strong pass involves being able to tell me that DNS is usually UDP based, and being able to describe what distinguishes TCP from UDP. A very strong pass involves being able to describe in detail recursive DNS queries, talk about the fact that DNS can use TCP rather than UDP for queries or replies larger than what fit in a single packet, being able to tell me a bit about how TCP congestion control, sequence numbers, acks, Nagle's Algorithm, and the like work.

I should point out that I recently talked to a college junior who got a "very strong pass" on this question as a front-end intern candidate. If she can do that as a front-end oriented candidate with only a couple of years of experience in school, I don't think it's unreasonable to expect a professional with several years of experience to have at least the basic knowledge that TCP exists.

Some people are stronger in one area than another; so I cover a number of areas, and expect them to do well on a majority, but not all, of the questions. Even if you fail this question, just saying that you don't know anything about networking, if you do well at all of the others we will bring you in for the in-person interview; we have recently hired someone who simply said "I don't know" on this question, and was a bit fuzzy on the big-O questions, but did fine on on all of the rest.