What Is DNS?
Every time you open a website, an invisible directory service translates the name you typed into a number your computer can reach. Here's how the Domain Name System works — and how to read what it publishes about any domain.
The internet's phone book
Computers don't browse by name — they connect to IP addresses. DNS, the Domain Name System, is the distributed directory that maps memorable names like example.com to those numbers. It was invented in 1983 precisely because the early internet's single host file in Stanford was becoming impossible to maintain.
Two things make DNS remarkable: it is distributed (no single machine knows everything), and it is cached everywhere (answers are remembered for a while, so lookups are fast). Both properties shape how the system behaves day to day.
What happens during a DNS lookup
When your browser asks for a website, a chain of DNS servers collaborates in a few milliseconds:
# 1. Your device asks its configured resolver (often your ISP's, or 8.8.8.8 / 1.1.1.1) # 2. The resolver, if it doesn't have the answer cached, walks the hierarchy: # root servers → ".com" servers → example.com's own name servers # 3. The domain's authoritative server answers with the actual records # 4. The resolver caches the answer for the record's TTL and replies to you
The last hop — the server that speaks for the domain itself — is what the NS records (below) point to. Everything above it is just delegation.
The record types that matter
A domain's DNS zone is a small database of typed records. These are the ones you will actually encounter:
| Type | What it does | Example |
|---|---|---|
| A | Maps a name to an IPv4 address | example.com → 93.184.216.34 |
| AAAA | Maps a name to an IPv6 address | example.com → 2606:2800::2201 |
| CNAME | Alias: points a name at another name | www.example.com → example.com |
| MX | Mail servers that receive the domain's email | 10 aspmx.l.google.com |
| TXT | Free text: SPF anti-spam, DKIM, ownership proofs | "v=spf1 -all" |
| NS | The authoritative name servers for the zone | ns1.examplehost.com |
| CAA | Which certificate authorities may issue TLS certificates | 0 issue "letsencrypt.org" |
| SOA | Zone metadata: primary server, contact, caching timers | ns1. dns-admin. … |
| PTR | The reverse: maps an IP back to a hostname | 8.8.8.8 → dns.google |
Two quirks are worth knowing: a CNAME is not allowed on the domain's root (that's why example.com uses A/AAAA records directly), and a domain with MX "0 ." has a null MX — a deliberate way of saying "this domain sends email but receives none".
Caching, TTL and propagation
Every record carries a TTL (time to live) — the number of seconds resolvers may reuse the answer before asking again. A 3600-second TTL means up to an hour of caching worldwide; a 60-second TTL means changes appear in under a minute.
This is what people mean by "DNS propagation": there is no broadcast of changes, just caches expiring at their own pace. Before a planned migration, the classic trick is to lower the TTL in advance, make the switch, watch it land everywhere quickly, then raise the TTL again to enjoy the caching.
Troubleshooting tip: if a site loads for others but not for you, your local resolver may still hold an old cached answer. Switching your device to 1.1.1.1 or flushing the DNS cache usually settles it.
Check any domain's DNS yourself
You don't need command-line tools — our browser utilities query Google and Cloudflare's resolvers live:
- DNS Checker — pull every record type of any domain in one click.
- Domain to IP — see just the addresses a domain points to, with hosting details.
- Reverse IP lookup — the PTR record: which hostname an IP answers to.
Learn more
- Curious about the numbers on the other side? Read what an IP address is or the IPv4 vs IPv6 comparison.
- Investigating an IP's reputation? See the IP blacklists guide.
DNS questions
What is DNS in simple terms?
DNS (Domain Name System) is the internet's phone book: it translates names you can type, like example.com, into the IP addresses computers actually connect to. Without it, you would have to memorise number addresses for every website.
What are the 8.8.8.8 and 1.1.1.1 addresses?
They are public DNS resolvers run by Google and Cloudflare. Your ISP runs one by default, but anyone can query these public ones instead — they are free, fast and often quicker to pick up DNS changes. Our DNS tools query both of them over encrypted DNS-over-HTTPS.
How long does a DNS change take to work everywhere?
As long as the record's previous TTL (time to live). Resolvers cache answers for the TTL duration — seconds to days — so after you edit a record, resolvers worldwide keep serving the old answer until their cached copy expires. Lower the TTL before a planned change to make the switch quicker.
What is the difference between DNS and an IP address?
An IP address is the number that identifies a device on the internet; DNS is the system that maps memorable domain names to those numbers. The domain is the name, the IP is the destination, and DNS is the translation between them.