Learning CoreDNS

Chapter 2. A DNS Refresher

So far, we’ve talked about practical matters like what CoreDNS is, what’s it’s good at (vis-à-vis DNS functionality) and what it’s not good at. Of course, that discussion had to include some DNS terminology—terminology that, in fairness, not everyone is familiar with.

We deliberated for a while over how much DNS theory to include in this book. We could, of course, “Begin at the beginning, and go on till... the end, then stop,” but that’s been done in other books, including books we’ve written. Still, it didn’t seem fair to send you out into the world without at least a grounding in DNS.

Our compromise is to try to give you just enough DNS theory to get by, and then to point you in the direction of, for example, DNS and BIND if you’re interested in more detail. (Hopefully that doesn’t seem too self-serving.)

What Is the Domain Name System?

The DNS is a naming system that maps names to other data, such as IP addresses, mail routing information, and more. And DNS isn’t just any naming system: it’s the internet’s standard naming system as well as one of the largest distributed databases in the world.

DNS is also a client–server system, with DNS clients querying DNS servers to retrieve data stored in that distributed database. Because the database is distributed, DNS servers will often need to query one or more other DNS servers to find a given piece of data. DNS clients are often called resolvers, whereas DNS servers are sometimes called name servers.