How DNS Lookups Work
When you type a domain name into your browser, a chain of questions and answers unfolds in milliseconds. Understanding this process helps explain why DNS is both powerful and occasionally problematic.
Think of it like asking for directions in an unfamiliar city. You ask someone nearby, they point you to someone who knows more, and you keep asking until you find someone who knows exactly where to go.
The Lookup Chain
Step 1: Check local cache. Your computer first checks if it already knows the answer from a recent lookup. If you visited the site moments ago, the IP address is probably cached locally.
Step 2: Ask the resolver. If not cached, your computer asks a recursive resolver — typically run by your ISP or a public DNS service. This resolver does the heavy lifting of finding the answer.
Step 3: Query root servers. If the resolver doesn't have the answer cached, it starts at the top of the DNS hierarchy — the root servers. These don't know specific addresses, but they know which servers handle top-level domains like .com, .org, or .uk.
Step 4: Query TLD servers. The resolver asks the appropriate TLD (Top-Level Domain) server. The .com server doesn't know google.com's IP address, but it knows which servers are authoritative for google.com.
Step 5: Query authoritative servers. Finally, the resolver asks the authoritative name server for the domain. This server has the actual DNS records and returns the IP address.
Step 6: Return and cache. The resolver sends the answer back to your computer. Both the resolver and your computer cache this result so future lookups are instant.
Recursive vs Authoritative
Two types of DNS servers play different roles:
Recursive resolvers do the work of chasing down answers. They query multiple servers on your behalf and cache results to speed up future requests.
Authoritative servers hold the actual DNS records for specific domains. They're the source of truth — when they answer, that's the definitive response.
Why This Matters
This multi-step process usually completes in under 100 milliseconds. But when DNS servers are slow, overloaded, or misconfigured, you'll notice delays or failures loading websites. Understanding the lookup chain helps you troubleshoot these issues.