The problem with this question is if someone gives a good answer, it can be hard to tell if they studied it or they actually know. Maybe you can suss this out with follow ups.
If they don't give a good answer, maybe they haven't looked into networking details and debugging for some reason -- a lot of junior people haven't, but they may have the aptitude to learn and be great at it, but just don't have the knowledge base yet. Although it depends on exactly what you're hiring for, too. If you need the person like me, who will find and fix your weird problems with networking, maybe they should know this, or be able to make fairly plausible guesses; but most people on my team don't need to do that (although it's always nice to have more).
The difference is if they studied the answer, but didn't grasp the material, they got information to pass the test (maybe), but probably didn't get useful information.
I guess if you stop at each point and ask 'what could go wrong here, and how would you debug it' and they answer that well, then they've gotten the information enough.
If they don't give a good answer, maybe they haven't looked into networking details and debugging for some reason -- a lot of junior people haven't, but they may have the aptitude to learn and be great at it, but just don't have the knowledge base yet. Although it depends on exactly what you're hiring for, too. If you need the person like me, who will find and fix your weird problems with networking, maybe they should know this, or be able to make fairly plausible guesses; but most people on my team don't need to do that (although it's always nice to have more).