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DNS (the Domain Name System) is the internet’s distributed, hierarchical naming system. When you enter a name such as www.example.com, your device normally asks a recursive DNS resolver for a particular record, such as an IPv4 or IPv6 address. The resolver either uses a valid cached response or follows referrals from the DNS root to the relevant top-level domain and then to the domain’s authoritative nameserver.
The result is not always one IP address. DNS can return several addresses, an alias, mail-routing information, or other resource records. DNS supplies that requested data; your browser then uses an address, if one was returned, to make the separate network connections needed to load a site.
What is DNS?
The Domain Name System lets people use memorable names while networks use structured records. Instead of requiring visitors to remember a numeric address, an application can request DNS data for a name such as www.example.com. DNS servers return the record type requested by the client.
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DNS is distributed rather than a single central directory. The namespace is divided into zones and delegated among many authoritative nameservers. A resolver performs the work of finding an answer on behalf of an application, while authoritative servers hold the original records for the zones they serve. This separation allows the system to scale and lets different organizations control their own portions of the namespace.
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The familiar web example is an address lookup, but the system is broader. An A record carries an IPv4 address, an AAAA record carries an IPv6 address, and a CNAME identifies an alias whose canonical target may need another lookup. DNS also supports records for mail routing and many other purposes.
How does DNS work?
A lookup begins with a client-side component, often called a stub or local resolver, asking a recursive resolver for a name and record type. The recursive resolver is commonly operated by an internet service provider, an organization, a router, or a public DNS provider. The following is the typical uncached sequence.
- The application requests a name. A browser, operating system service, or other program asks for a record for a hostname. The request identifies the name and type, such as A for IPv4 or AAAA for IPv6.
- The local component sends the request to a recursive resolver. The client usually does not contact root or authoritative nameservers directly. It relies on the configured recursive service to search for the answer.
- The resolver checks its cache. If it has a usable, unexpired response, it can return that data immediately. A cache hit means this request may finish without any query to the DNS hierarchy.
- The resolver asks a root nameserver when it needs a referral. The root does not normally contain the requested website address. It identifies which nameservers are authoritative for the relevant top-level domain, such as
.com. - The resolver asks a TLD nameserver. The
.comnameservers, for example, provide delegation information identifying the authoritative nameservers for the registered domain, such asexample.com. - The resolver asks the domain’s authoritative nameserver. That server holds the original records for its zone and returns the requested data for the hostname. If the response is a CNAME, the resolver may follow the alias and obtain the address record for the canonical target.
- The resolver returns the response and caches it when permitted. The answer travels back to the client. The resolver can retain the record for its time to live, or TTL, and serve later requests from cache until that period expires.
This root-to-TLD-to-authoritative path describes what happens when the resolver lacks a usable cached answer. It is not a mandatory sequence for every lookup: a cache hit can provide the result earlier.
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Suppose an application asks for an A record for www.example.com. The recursive resolver first checks whether it already knows a valid answer. If not, it asks a root nameserver where to find the .com authority. A .com nameserver then identifies the nameservers delegated for example.com. The authoritative server for that domain supplies the A record, or supplies a CNAME that points to another name whose address must be resolved. The recursive resolver returns the final requested data to the application and records the response with its TTL.
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What is a DNS resolver?
A DNS resolver is the part of the process that accepts a client’s question and obtains an answer. Two resolver roles are easy to confuse:
| Component | What it does | What it normally knows |
|---|---|---|
| Stub or local resolver | Runs on or near the client and sends the application’s request to a recursive DNS service. | Usually the address of the recursive resolver to use, plus local operating-system or application state. |
| Recursive resolver | Receives the client request, checks cache, follows referrals, and returns a response. | Cached records and the information needed to query root, TLD, and authoritative servers as required. |
| Root nameserver | Provides referrals to the nameservers responsible for top-level domains. | Information about TLD authorities, not every domain’s individual address record. |
| TLD nameserver | Provides delegation information for domains within a top-level domain such as .com. |
The authoritative nameserver information for registered domains in that TLD. |
| Authoritative nameserver | Returns the original records for names in the zone it serves. | The zone data published by the organization responsible for that domain or delegated subdomain. |
In everyday explanations, “DNS server” can refer to any of these systems. The distinction matters: a recursive resolver searches on a client’s behalf, while an authoritative nameserver answers from the zone data it controls. Root and TLD nameservers connect the delegations; they are not interchangeable with the authoritative server for a particular website.
How does a domain name get translated into an IP address?
“Translated” is useful shorthand, but DNS does not perform a simple one-name-to-one-number conversion. It looks up a requested resource record. A name can have multiple address records, point to an alias, or have no address record at all while still carrying other DNS data.
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| Record type | Data it provides | How it affects a web lookup |
|---|---|---|
| A | An IPv4 address. | Gives a client an IPv4 destination for the hostname. A name may have more than one A record. |
| AAAA | An IPv6 address. | Gives a client an IPv6 destination when IPv6 connectivity is available. A name may have more than one AAAA record. |
| CNAME | An alias to another canonical name. | Requires the resolver to look up the target name to obtain the requested address data. |
| Mail and other records | DNS data for services such as mail routing and other applications. | These records show why DNS is a general naming system, not only a web-address directory. |
If both A and AAAA records exist, the client and its networking stack determine which usable address to try. DNS itself is supplying the records; it is not choosing the complete application connection strategy. Likewise, a CNAME is not an IP address. It names another host, and resolution continues until the requested data is obtained or the lookup fails.
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Recursive versus authoritative DNS: what is the difference?
The simplest distinction is responsibility. A recursive resolver is client-facing and performs discovery. An authoritative nameserver is data-facing and publishes the answer for its zone.
- Recursive service: accepts a question such as “What is the A record for
www.example.com?”, searches its cache, contacts other DNS servers when needed, and sends one response back to the client. - Authoritative service: answers for names in a zone from the records maintained by the zone’s operator. It does not need to discover its own zone data by asking the root.
- Root and TLD services: provide referrals that let a recursive resolver move toward the correct authority.
A recursive resolver may temporarily store information learned from authoritative answers, including delegation data, so future requests can avoid repeating every step. That cache does not make the resolver authoritative for the domain: it is still serving retained data under the limits of the records’ TTLs.
Cached and uncached DNS lookups
Caching is why many repeated lookups finish without a visible trip through the hierarchy. The resolver stores a response only for the period allowed by its TTL. Different resolvers, devices, and applications can therefore be at different points in the cache cycle.
| Situation | What the resolver does | Typical consequence |
|---|---|---|
| Usable cache entry | Returns the retained record without querying the root, TLD, or authoritative server for this request. | Lower lookup delay and less DNS traffic. |
| No usable cache entry | Follows referrals through the hierarchy until it receives the requested data or an error. | More DNS queries are needed before the client receives an answer. |
| Record changed but old TTL remains | Continues serving the older cached value until that value expires. | Some users see the new destination before others. |
What is DNS TTL, and why do DNS changes take time?
TTL means time to live. In the DNS standards, it is expressed in seconds and tells a resolver how long it may retain a record before discarding it and obtaining fresh data. A longer TTL can reduce repeated queries but keeps an old value available for longer after a change. A shorter TTL allows changes to be fetched sooner but can require more resolver traffic.
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TTL is not a promise that every browser, operating system, router, and recursive resolver refreshes at exactly the same moment. Applications and local components may maintain their own state, and different recursive resolvers may have cached the previous response at different times. Consequently, changing an authoritative record does not make every user see the new result simultaneously.
When investigating a change, identify which record type changed, ask which recursive resolver the affected client uses, and allow the previous TTL to expire. Also check whether the hostname is a CNAME: the alias and its target can have separate records and TTLs, so changing only one part may not produce the expected result immediately.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.What happens after DNS returns an address?
DNS is only the naming step. Once the client receives an address, the browser or another application uses normal network protocols to contact that destination. It may establish a transport connection, negotiate encryption, send an HTTP request, follow redirects, and download page resources. A successful DNS response therefore does not prove that the website is reachable, that the server is healthy, or that the requested page exists.
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The reverse is also possible: a site can be reachable by address while a DNS problem prevents users from finding it by name. Separating name resolution from later network and application steps makes troubleshooting more precise.
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Common DNS misconceptions and failure points
“The root server contains every website’s IP address.”
It does not. Root nameservers provide information about which nameservers are authoritative for top-level domains. The TLD and domain delegations lead the recursive resolver to the authority that holds the requested zone record.
“Every lookup starts at the root.”
Not when a recursive resolver has a valid cached answer or cached delegation information. The resolver may contact the hierarchy only when it lacks usable data.
“A domain always maps to one IP address.”
A name can have multiple A or AAAA records, can use a CNAME alias, or can publish records for services other than web addressing. The requested record type determines what data the resolver returns.
“A DNS change is broken because one device still shows the old address.”
Check TTL and caching first. The device, its local resolver, or an upstream recursive resolver may still have an unexpired response. Compare results through the resolver used by the affected network and through the authoritative server to determine whether the published data or only a cache is stale.
“DNS delivered the webpage.”
DNS supplied naming data. The subsequent connection, encryption, HTTP exchange, and content delivery are separate operations that can fail independently.
Why the hierarchy matters
Delegation lets the namespace grow without requiring one database or one operator to hold every record. Root nameservers point to TLD authorities, TLD authorities point to domain authorities, and those authorities publish records for their zones. Recursive resolvers hide that distributed search from applications and improve performance by caching results.
ICANN describes this design in ICP-3: A Unique, Authoritative Root for the DNS (2012), stating that the DNS hierarchy begins with a group of root nameservers that provide information about which computers are authoritative for top-level domains. The underlying concepts are specified in the DNS standards RFC 1034, Domain names — concepts and facilities, and RFC 1035, Domain names — implementation and specification, both published in November 1987. Modern overviews from Google Cloud and Cloudflare describe the same separation between recursive resolution, authoritative data, records, and caching.
Quick Recap
A concise mental model
- Name: The application has a human-readable hostname and a requested DNS record type.
- Ask: A stub or local resolver sends that question to a recursive resolver.
- Check: The recursive resolver uses a valid cache entry if one exists.
- Refer: Without a usable answer, it follows root, TLD, and domain-authority referrals.
- Answer: The authoritative server supplies the zone’s record, possibly an alias that requires another lookup.
- Cache and connect: The resolver returns the data and caches it for its TTL; the application then uses an address, if supplied, for the separate network connection.
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