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Learn · Lesson 3

How DNS works: what happens when you type a domain name

DNS is the internet’s directory. It turns the name you type into the address your device needs, usually in well under a second, and nobody is in charge of the whole list.

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The short version

  • DNS, the Domain Name System, looks up the records for a name. Most often that’s the IP address of a website.
  • No single server knows every answer. A resolver asks in three hops: the root, then the registry for the ending, then the domain’s own nameservers.
  • Answers are remembered (cached) for a time set by each record’s TTL.
  • That’s why a DNS change doesn’t show up everywhere at once. Nothing is being pushed out; old answers are expiring.

Who’s involved in a lookup

Four kinds of server take part. Knowing which is which makes the rest of DNS much less mysterious.

WhoWhat it doesRun by
ResolverDoes the asking on your behalf and remembers the answersYour internet provider, or a public service
Root serversKnow which servers handle each ending (.au, .com)A dozen organisations around the world
TLD serversKnow which nameservers answer for each registered nameThe registry for that ending
Authoritative nameserversHold a domain’s actual records and give the final answerWhoever hosts that domain’s DNS

“Authoritative” is the word to remember. RFC 9499, the DNS terminology standard, defines an authoritative server as one “that knows the content of a DNS zone from local knowledge, and thus can answer queries about that zone without needing to query other servers”. Everyone else in the chain is passing the question along or repeating an answer they heard earlier.

One lookup, step by step

Say you type www.yourname.com.au and nothing has been looked up before.

A DNS lookup in six steps Your device asks a resolver. The resolver asks a root server, which refers it to the .au servers. The .au servers refer it to the nameservers for yourname.com.au, which answer with the address 203.0.113.10. The resolver passes the answer back to your device, which then connects to the web server at that address. Your device phone or computer Web server 203.0.113.10 6 1 5 Resolver run by your internet provider or a public service keeps a copy of each answer (cache) Root servers know every ending “Not me. Ask .au.” 2 .au servers run by the registry “Ask its nameservers.” 3 Nameservers for yourname.com.au “It’s 203.0.113.10.” 4
Dark arrows are questions; green arrows are answers. The numbers match the steps below.

  1. You ask

    Your device asks its resolver: “What’s the address for www.yourname.com.au?”

  2. The root points the way

    The resolver asks a root server. It doesn’t know the address, but it knows which servers handle .au.

  3. The registry points closer

    The .au servers don’t know the address either. They know which nameservers answer for yourname.com.au.

  4. The nameservers answer

    Those nameservers hold the domain’s records, and reply with the address.

  5. The answer comes back

    The resolver hands the address to your device and keeps a copy for next time.

  6. You connect

    Your device connects to that address and the page loads. DNS has done its job.

Notice what steps 2 and 3 have in common: each server answers with “not me, ask them”. That hand-off is called a referral, and it’s how a system with no central list still finds everything. Each level only needs to know who is responsible for the level below.

A note on the root servers

The root sounds like a single machine. It isn’t. IANA describes the root servers as “a network of hundreds of servers in many countries around the world”, “configured in the DNS root zone as 13 named authorities”. They’re operated by a dozen different organisations, among them Verisign, NASA, ICANN and RIPE NCC.

Caching and TTL: why DNS is fast

If every lookup took all six steps, the internet would crawl. So resolvers remember answers. Every DNS record carries a number called the TTL, for time to live. The DNS specification, RFC 1035, defines it as “the time interval that the resource record may be cached before the source of the information should again be consulted”.

A TTL of 3600 means “you can reuse this answer for an hour”. Until the hour is up, the resolver answers from memory without asking anyone. Your device and your browser keep their own short-term copies too.

Why changes don’t show up straight away

You’ll hear that a DNS change “takes time to propagate”, as if the update were slowly spreading across the world. Nothing is spreading. Your nameservers have the new answer the moment you save it. What takes time is every resolver’s old copy running out.

Why two people see a DNS change at different times A timeline. Resolver A looked the record up just before the change, so it keeps giving the old answer until its cached copy's TTL runs out, then gets the new one. Resolver B had nothing cached, so it gets the new answer straight away. Resolver A looked it up a minute before the change old answer, still cached new answer you change the record its TTL runs out Resolver B hadn’t looked it up nothing cached new answer straight away you change the record
Same change, same moment, two different experiences. It depends on what each resolver already had in memory.

So one person sees the new website straight away while a colleague at the next desk, on a different network, still sees the old one. Both are right, for now.

  • The wait is at most the old TTL. If the record had a TTL of one hour, everyone has the new answer within an hour or so.
  • Plan ahead for big moves. Lower the TTL a day or two before you switch hosts, make the change, then raise it again once things are settled.
  • Changing nameservers takes longer than changing a record, because the registry’s own records have TTLs you don’t control. Allow a few hours, and up to two days to be safe.

“It doesn’t exist” is cached too

If you look up a name before its record has been created, the “no such record” answer is remembered as well. RFC 2308 calls this negative caching: “the storage of knowledge that something does not exist”. So if you check a brand-new subdomain a moment too early, you may have to wait out that cached “no” even after the record is in place.

What DNS doesn’t do

DNS only answers the question “where?”. It doesn’t carry your website or your email; it tells other computers where to find them. That makes troubleshooting simpler than it looks:

  • If the lookup gives the wrong address, or none, it’s a DNS problem.
  • If the lookup gives the right address and the site still won’t load, the problem is at the web host.

You can check the first half yourself. The DNS tab in our toolbox shows the records the world currently sees for any domain, with their TTLs.

Next: the answers themselves. DNS records explained covers A, CNAME, MX, TXT and the rest. Then Nameservers and DNS zones covers step 3 of the lookup in detail: who decides which nameservers get asked.

Terms in this lesson

DNS
The internet’s directory.
Resolver
The server that does DNS lookups on your behalf and remembers the answers.
Root zone
The very top of the DNS, written as a single dot.
Authoritative nameserver
A nameserver that holds a zone’s actual records and gives the final answer, as opposed to a resolver repeating an answer it heard earlier.
Cache
A stored copy of an answer.
TTL
The number of seconds an answer may be reused before it has to be looked up again. 3600 is one hour.
Propagation
The wait after a DNS change before everyone sees it.

Every term, in full, is in the glossary.

Sources

All read on 2 October 2026.

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