Posted on Jul 10

Understanding Recursive Resolvers in DNS

As I was exploring the backend engineering roadmap on roadmap.sh, I stumbled upon an interesting concept: the recursive resolver. It struck me as a key part of how the internet works, and since teaching is a great way to solidify my own understanding, I thought I’d share what I’ve learned so far.

🕵️ What Exactly Is a Recursive Resolver?

In simple terms, it’s like a helpful detective that steps in when your device needs to find the IP address for a website domain (like www.google.com). When you type a URL into your browser, it doesn’t automatically know where to go—that’s where DNS (Domain Name System) comes in. The recursive resolver takes on the task of querying the right servers to get that information.

⚙️ How Does It Work?

Here's how I understand the process:

The recursive resolver first checks its own cache—a sort of short-term memory—to see if it already knows the answer from a previous query.
If it finds the IP address there, it sends it back to your device immediately, saving time.
If not, it starts querying DNS servers in sequence:
- First, it asks the Root DNS servers.
- Root servers respond with a referral to TLD (Top-Level Domain) servers like .com or .org.
- TLD servers then point to the authoritative name servers responsible for the specific domain (like google.com).
The authoritative server returns the correct IP address.
The recursive resolver passes it back to your device and stores it in cache for future use.

This caching is super useful—it acts like a notebook of addresses you’ve looked up before, so the resolver doesn’t need to do all that work again next time.

🧠 Why It Matters

This mechanism is a big part of what keeps the internet fast and reliable. Without recursive resolvers, every time you typed in a website, your device would have to go through the entire chain of DNS servers from scratch.

It’s amazing how something so behind-the-scenes plays such a crucial role in our daily internet experience.

💬 Final Thoughts

I’m still wrapping my head around the deeper technical details, but even this overview has made me appreciate how well-engineered DNS is. If you’ve got insights to add or corrections to make, feel free to drop a comment—I'm always eager to learn more!