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Network Bytes · Episode 6 · CCNA 4.3

What is DNS?

Your computer has no idea what "google.com" means. DNS, the internet's contacts app, turns the names you type into the IP addresses computers use.

Posted · About a 1 minute watch, 2 minute read · Take the quiz

Names are for humans, numbers are for computers

When you type example.com, your computer can't do anything with the name itself. Devices on a network find each other using IP addresses, like 203.0.113.10. Names exist because they're easy for people to remember. Nobody wants to memorize a string of digits for every website they visit.

So something has to translate the name into a number. That's the job of DNS, the Domain Name System.

The internet's contacts app

Think of the contacts app on your phone. You tap a name, and the phone looks up the number for you. DNS works the same way:

  1. You type a name, like example.com.
  2. Your device asks a DNS server: "What's the number for this name?"
  3. The server looks it up and sends back the IP address, like 203.0.113.10.

Remembering recent answers

Your device also keeps a short list of recent answers for a while. This is called caching. If you visit the same site again soon, your device already knows the number and doesn't have to ask again. That saves time on the sites you visit a lot.

Answers don't stay in the list forever. Each one comes with a time limit, and when it runs out the device asks again, so the list stays up to date.

Then the browser connects

Once your device has the number, your browser connects to it and the page starts loading. The whole lookup usually happens in milliseconds, before the page even begins to load.

Try it yourself

On a computer, open a terminal (Command Prompt on Windows, Terminal on a Mac) and type:

nslookup example.com

You'll see the name of the DNS server your computer asked, and the IP address it sent back for example.com.

Good to know

  • This is a simplified picture. A real lookup usually goes to a recursive resolver (often run by your internet provider), which can ask a chain of other servers (root, top-level domain and authoritative servers) to find the answer. That chain gets its own lesson later.
  • The addresses in the video (203.0.113.10 and similar) come from ranges set aside for examples and documentation, not real websites.
  • Caching happens in more than one place: your browser, your operating system and the DNS resolver can each keep recent answers.

For CCNA learners

This lines up with CCNA 200-301 exam topic 4.3, explain the role of DHCP and DNS within the network: know that DNS resolves names to IP addresses and that clients use a configured DNS server to do it.

Test your knowledge

Quick quiz: What is DNS?

4 multiple-choice questions. Pick one answer for each, then check how you did.

1What does DNS do?
2What does your device ask the DNS server?
3Why does your device remember recent DNS answers?
4In the contacts-app comparison, what is the IP address like?

Sources

Video transcript

Here's a secret: your computer has no idea what "google dot com" means.

Computers find each other using numbers called IP addresses. Names are for humans. Nobody wants to memorize a string of digits for every website they visit.

So who translates? DNS, the Domain Name System. Think of it as the internet's contacts app. You type a name, and your device asks a DNS server, "What's the number for this name?" The server looks it up and sends back the IP address.

Your device also remembers recent answers for a while, so it doesn't have to ask again every single time. That saves time on sites you visit a lot.

Then your browser connects to that number. All of this happens in milliseconds, before the page even starts loading.

That's your bite. Next: what happens the instant you press Enter.

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