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.
The problem with "I don't know" is that it's really not culturally appropiate to say! Americans are supposed to be rugged, resourceful individualists and asking for help is frowned on because it shows weakness. Can't do that in an interview!
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.