How Browsers Use DNS

When you type a web address like www.example.com into your browser, something important happens before any webpage appears. Your browser doesn't actually know where example.com lives on the internet — it only understands IP addresses. So the very first step is translating that human-friendly name into a numerical address.

This translation process uses the Domain Name System, and it happens automatically every time you visit a website. Think of it like checking an address before mailing a letter — you need to know exactly where to send it before anything else can happen.

The Lookup Process

When your browser needs to resolve a domain name, it follows a specific sequence. First, it checks its own memory to see if it recently looked up this same domain. Browsers maintain a cache of recent DNS lookups to avoid repeating work.

If the browser doesn't have the answer cached, it asks your operating system. Your computer also keeps its own DNS cache. If neither has the answer, the request goes out to a DNS resolver — typically provided by your internet service provider or a service like Google's 8.8.8.8.

This resolver then queries the DNS hierarchy, as covered in How DNS Lookups Work, eventually returning the IP address your browser needs.

Why Caching Matters

DNS lookups add time to every web request. Even though they're fast — often just milliseconds — those milliseconds add up. Caching at multiple levels dramatically speeds up browsing.

When you visit a website repeatedly, your browser likely uses a cached IP address rather than performing a fresh lookup each time. This is why the first visit to a new site sometimes feels slightly slower than subsequent visits.

However, caching can occasionally cause problems. If a website changes its IP address, your cached information becomes outdated. Most DNS records include a "time to live" (TTL) value that tells caches when to refresh their information.

What Happens Next

Once the browser has the IP address, it can establish a connection to the server and send the actual HTTP request. The DNS lookup is invisible to you as a user, but it's a critical first step in every web interaction.