Writing a simple DNS resolver is a common assignment in networking courses, and I do recommend it --- keeping in mind that the protocol was designed to work on machines with a fraction of the memory and CPU power as those today, helps understanding some of the otherwise odd design decisions; for example, requests and replies have the same format and header to allow the same buffer to be reused for both receiving the…
I was going to post complaining about that very point. Any discussion of URL is irrelevant and misleading in the context of raw DNS queries for beginners. I think the author incorrectly assumes domain name is interchangeable with URL for some reason.