How DNS Works

Have you ever updated your site’s DNS records, nothing changed, and you had no idea why? This zine is for you!

DNS has a bad reputation. It has terrible terminology, it’s totally invisible what’s happening behind the scenes, changes take a seemingly arbitrary amount of time to be applied, there are literally millions of computers that could be caching your records, there’s often no way to clear the caches, and if you mess it up you can take your site down for hours. Great.

And DNS is also everywhere! You have to set it up every time you create a new domain, so most of us come into contact with it at some point. Most people use it very infrequently, so it’s very normal to just copy and paste DNS records without understanding what they mean and hope for the best.

But it doesn’t have to be that way! DNS’s basic design is actually relatively straightforward and hasn’t changed since DNS was invented in the 1980s.

Because the core design of DNS doesn’t change, you can learn how it works once and then manage your DNS records with confidence for the rest of your life.

We’ll explain:

• How DNS resolvers work, including a working implementation in Python (and how they can lie to you)
• Every weird thing I know about DNS caching (like negative caching and resolvers that don’t respect your TTLs)
• How to configure dig (my favourite DNS query tool) to give you human-readable output
• The 6 most common DNS record types you’ll see in practice (A, AAAA, CNAME, MX, TXT, and NS)

This zine also comes with a free playground (Mess With DNS) where you can experiment with DNS and break things.