DNS and Name Resolution

The Domain Name System (DNS) is the Internet's phonebook. It translates human-readable domain names (like example.com) into IP addresses (like 93.184.216.34) that computers use to identify each other. Without DNS, you would need to memorise IP addresses for every website.

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How DNS Works — The Big Picture

When you type www.example.com into your browser:

1. Browser cache    → Is it already cached? If yes, done.
2. OS cache         → Check the local DNS cache
3. /etc/hosts       → Check the local hosts file
4. Resolver         → Ask your configured DNS resolver (e.g., ISP or 8.8.8.8)
5. Root server      → "I don't know, but .com is handled by these TLD servers"
6. TLD server       → "example.com is handled by these authoritative servers"
7. Authoritative    → "www.example.com is 93.184.216.34"
8. Response cached and returned to the browser

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DNS Hierarchy

DNS is organised as a hierarchical, distributed database:

                    . (Root)
                   / | \
                 /   |   \
              .com  .org  .uk    ← Top-Level Domains (TLDs)
              /       |      \
         example   wikipedia  bbc   ← Second-Level Domains
            |         |        |
          www       en        www    ← Subdomains / Hosts

Components