I strongly agree with the sibling comment that this is a perfectly valid interview question.

One of the biggest red flags in an interview is if I ask a question and the person doesn't know how to say 'I don't know', because it suggests there's a big risk that if I assign them a task in their day-to-day work, they won't tell me if they feel unprepared to tackle it. That's a far bigger issue than not knowing that traceroute uses variable TTLs to figure out the timing along the route.