DNS is the service that turns a website name into the IP address of the server where it is hosted. Without it a browser would not know where to send a request: a person types a name, while the network only works with numeric addresses.
How a browser finds a server by site name
One DNS query passes through several steps before a browser gets an address. Each step either answers right away from a cache or passes the question further.
- The browser checks its own cache — if the name was requested recently, the answer is ready.
- If there is no cache entry, the request goes to the operating system, which keeps its own cache of records.
- The operating system asks a resolver — usually a server run by the internet provider.
- The resolver asks the root servers, which point to the servers of the top-level domain zone.
- The domain's authoritative server returns the exact IP address, and the resolver passes it to the browser.
What a DNS zone record is
A domain zone stores records — lines that say where to send different kinds of requests. Each record has a type, and the type defines what it stores.
| Type | What it points to | Typical use |
|---|---|---|
| A | IPv4 address of the server | The main link between the domain and the server |
| AAAA | IPv6 address of the server | The same link for an IPv6 network |
| CNAME | Another name instead of an address | A subdomain that points to the main domain |
| MX | Mail-receiving server | Delivery of mail to the domain |
| TXT | Arbitrary text | Domain ownership confirmation, mail policy rules |
| NS | Name servers of the zone | Who is responsible for the domain's records |
What TTL is and why changes are not visible right away
TTL (Time To Live) is the time, in seconds, for which a resolver remembers an answer. While the TTL has not expired, the resolver returns the stored answer instead of asking the authoritative server again.
That is why an edited record does not take effect instantly: some visitors still see the old value until their resolver refreshes its cache. A detailed look at the timing is in the article about DNS propagation.
Does DNS affect site speed
DNS only affects the very first request to a domain — while the resolver is looking up the answer and has not cached it yet. After that the record sits in the cache, and repeat requests do not touch it.
The delay at this step is measured in milliseconds and, against the background of loading a page (requests to the server, style files, images), is usually unnoticeable. The exception is domains with a chain of several CNAME records in a row: each step adds its own lookup hop.
A public resolver or your own NS server — what is the difference
These are two different roles that are often confused. A resolver is the one your computer asks the question "what address does this domain have". An NS server is the one that stores the answer and is responsible for the domain's own zone.
A public resolver (from a provider or a third-party service) simply passes the question further and caches the answer. The domain's NS servers are the source of truth: that is where the question ends up if no cache has the answer.
Where to check your domain's records
Two utilities show the current zone records directly, bypassing the browser cache.
dig example.com A # Shows the domain's A record
nslookup -type=MX example.com # Shows the mail-receiving serversWhat to do next
If a record needs to be changed or added, the steps are described in the article on how to set up DNS for a domain. After editing, keep TTL in mind: the previous value may still be visible to some visitors for a while.