DNS, the Domain Name System, is the internet's address book. It translates human-friendly domain names such as mozilla.org into the numeric IP addresses that computers use. When you visit a website, a resolver asks a chain of DNS servers until one with authority over that domain gives the answer.
Type a website name into your browser and a page appears in a blink. Behind that blink, a quiet system has just worked out which computer on the internet holds the site you asked for. That system is DNS.
Here's a plain-English tour, drawn from MDN Web Docs and the Wikipedia entry on the Domain Name System. You don't need technical skills. If you've ever registered a domain, moved a website or wondered why an email setting 'takes a while to update', this will make it clearer.
DNS meaning: the internet's address book
MDN describes DNS, the Domain Name System, as a hierarchical and decentralised naming system for internet-connected resources. It keeps a list of domain names along with the resources, such as IP addresses, that go with them.
Its best-known job, in MDN's words, is translating human-friendly domain names like mozilla.org into numeric IP addresses such as 192.0.2.172. People are good at remembering names and computers need numbers, so DNS sits in the middle and translates. That translation step is called a DNS lookup.
What happens during a DNS lookup
Wikipedia explains that the client side of DNS is called a resolver. When you visit a site, your application asks the resolver built into your operating system. The resolver checks its cache first, and if the answer isn't there it asks designated DNS servers, usually the ones run by your internet provider.
If those servers don't know either, the search works its way down the hierarchy:
- The resolver asks a root server. Root servers usually don't give the final answer but point the resolver to more specific servers, such as those responsible for the .org part of a name.
- Those servers refer the resolver onwards to the servers that look after the particular domain.
- A server with authority over the domain gives the answer, and the resolver passes the address back to your browser.
- Your browser connects to that address and loads the page.
Wikipedia notes that resolvers start with a built-in list of root server addresses, and that there are thirteen groups of root name servers, with extra copies spread around the world.
The address-book analogy
Think of a very large, shared phone book that nobody owns in one place. Instead of one giant book, DNS splits the work into sections. The root tells you where to find each top-level ending, each ending tells you who looks after a given domain, and that final keeper knows the real address. It's a chain of 'try this person next' until someone has the answer.
DNS record types you may have seen
A domain's settings are stored as records. Wikipedia lists the most common types:
| Record | What it does | Plain-English example |
|---|---|---|
| A | Maps a domain name to an IPv4 address | Points your website name at its server |
| AAAA | Maps a domain name to an IPv6 address | Same job, newer style of address |
| CNAME | Provides an alias for another domain name | Makes one name follow another |
| MX | Names the mail exchanger that handles email for the domain | Tells the world where your email goes |
| NS | Lists the name servers that can answer for the domain | Says who holds the official records |
If you've ever been told to 'add an MX record' when setting up business email, this is where it lives.
Why DNS changes take time to spread
Each record carries a time to live, or TTL, set by whoever manages the domain. According to Wikipedia, a TTL can range from a few seconds to several days or even weeks. Caching saves DNS servers from answering the same question over and over, but it also means a change doesn't show up everywhere at once. Caches have to expire first, and some resolvers override the TTL values they're given.
That's why a new website address or email setting can work for you and not for a colleague. It isn't broken, it's just waiting for old answers to expire.
Want AI doing the heavy lifting in your marketing?
I build the systems that handle the boring 80 percent, so you get your week back. Done properly, with the human kept in.
A short history of DNS
The system is older than most people expect. Wikipedia says the original specifications, RFC 882 and RFC 883, were published in November 1983, and RFC 1034 and RFC 1035 replaced them in November 1987. The system has been extended many times since, yet the basic idea of a hierarchy of names has stayed.
Staying careful with DNS settings
Because DNS decides where your domain points, it's worth treating your domain account like a bank login. Use a unique, strong password and a second login step, and keep a note of your current records before changing anything so you can put them back if needed.
Developers often keep DNS and configuration details in tracked files, which is one use for version control. If that's new to you, what Git is explains the idea in plain terms.
Explain how the web works to others
DNS trips up almost everyone at first, so patient, clear explanations are valuable.
Engineers with something to teach can find developer sites open to outside authors on this page.
Frequently asked questions
What does DNS stand for?
DNS stands for Domain Name System. MDN describes it as a hierarchical and decentralised naming system for internet-connected resources.
What's a DNS server?
It's a server that can answer questions about domain names. Resolvers ask DNS servers, and a server with authority over a domain gives the final answer.
Why does a DNS change take time to show up?
Records are cached for a period set by their TTL, and old answers need to expire before everyone sees the new one.
What's the difference between an A record and an MX record?
An A record maps a domain name to an IPv4 address, while an MX record says which mail exchanger handles email for the domain.
Is DNS the same as a domain name?
No. A domain name is the name itself. DNS is the system that translates that name into an address.
