Think it through together · A little story
Imagine a DNS lookup as a book-finding game: a girl asks the desk, and the desk follows a directory to find the shelf responsible for that book.
Lay out the process
- Recursive resolverTakes on the lookup
- Root and top-level domain referralsPoint to the next stop
- Authoritative serverProvides the record it manages
- Return and cacheMake the result available for use
When no usable cache is available, a resolver can follow the hierarchy to find an authoritative answer.
The root service points toward a top-level domain. The top-level domain service then points to the relevant authoritative server, which returns the record it manages. Real lookups may include extra steps, such as following aliases.
If a result is cached, some steps can be skipped; a lookup does not have to visit every stop in the diagram every time.
Your turn to try
If an authoritative server says “this name does not exist,” should you substitute the IP address of some similar-looking name?
Have you thought it through? Open for an explanation
No. “Does not exist” is a meaningful result. A program should handle it according to the rules instead of guessing an address.
Take away one discovery
When no usable cache is available, a resolver can follow the hierarchy to find an authoritative answer.
Try covering the diagram above and explaining each step to someone in your family. If one step is hard to explain, go back and look at that card again.