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A worked example

A name becomes an address

One exchange at a time. Read what changes, then explain it in your own words before moving on.

  1. Meet the components
  2. Follow the steps
  3. Compare an example
  4. Check your understanding
Interactive Lab

A name becomes an address

Follow the resolver through referrals and watch a cached answer bypass the hierarchy.

Steps1. example.com? 2. Where is .com? 3. TLD referral 4. example.com? 5. NS referral 6. A / AAAA? 7. Address + TTL 8. Address
Click a box or choose its name to learn what it means.
BrowserReadyResolverReadyRoot DNSReadyTLD DNSReadyAuthoritativeReadyBrowserReadyResolverReadyRoot DNSReadyTLD DNSReadyAuthoritativeReady
Ready to traceCold lookup
Before you start · 8 stepsCold lookup

This simplified recursive lookup starts without useful cached answers or referrals.

How to use this example

Select Next step to read at your own pace, or Animate step to watch one exchange. Nothing advances until you choose.

Inspect components & read every step
  • Browser

    The program you use to open websites.

    Example: Your browser requests a web page and displays the response.

  • Resolver

    A DNS service that finds address information on behalf of your device.

    Example: It checks its cache or asks DNS servers where to find a website.

  • Root DNS

    The top level of DNS that points a resolver toward the relevant top-level domain servers.

    Example: For a .com name, it provides a referral toward .com DNS servers.

  • TLD DNS

    DNS servers for a top-level domain, such as .com, that provide referrals to authoritative servers.

    Example: The resolver learns which servers handle the requested domain.

  • Authoritative

    The DNS server responsible for answering with records for a particular zone.

    Example: It supplies the configured address record for a name in that zone.

Cold lookup

This simplified recursive lookup starts without useful cached answers or referrals.

  1. Browser Resolver: example.com?. The client asks its configured resolver.
  2. Resolver Root DNS: Where is .com?. The resolver asks the root for a referral.
  3. Root DNS Resolver: TLD referral. Root supplies referral information, not the final website address.
  4. Resolver TLD DNS: example.com?. The resolver asks the TLD server.
  5. TLD DNS Resolver: NS referral. The resolver learns the authoritative service.
  6. Resolver Authoritative: A / AAAA?. The resolver asks for the address record.
  7. Authoritative Resolver: Address + TTL. The answer can be retained for its TTL.
  8. Resolver Browser: Address. The browser can begin connecting to the destination.

Warm cache

A valid cached answer avoids another trip through the DNS hierarchy.

  1. Browser Resolver: example.com?. The client requests the same name.
  2. Resolver Browser: Cached address. The remaining TTL permits reuse.

Fictional teaching trace. One moving dot represents an exchange, not a measured network capture.