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DNS is not one central phonebook. It is a hierarchical namespace divided into zones, with authority delegated from parent zones to child zones. When you look up a name, a recursive resolver follows that authority—or uses information it already has cached—to return the requested record.
How does DNS work?
DNS, the Domain Name System, maps names such as www.example.com to records, including the addresses a browser may need to connect to a website. Its design has two parts: a tree of names and a distributed set of zones that hold authoritative data. A resolver finds the relevant data by asking servers, following referrals when necessary, and reusing cached results when possible.
As RFC 1034 puts it, “The domain name space is a tree structure.” A domain name is a sequence of labels along a path through that tree: in www.example.com, the labels are www, example, and com. The root of the tree is written as a final dot in the fully qualified name, though people usually omit it.
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The name tree is divided into zones: connected parts of the namespace for which an operator’s name servers provide authoritative data. A zone can include names beneath a domain, while a subdomain can be delegated into a separate child zone managed independently.
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Delegation is recorded in the parent zone. At the boundary—called a zone cut—the parent publishes NS records identifying the child zone’s name servers. A resolver that reaches that boundary can follow the referral to the child’s servers. If a child’s name server is named within the child zone itself, the parent may also need to provide glue address records; otherwise, learning the server’s address could require resolving through the very child zone the resolver has not reached yet.
This is why DNS is distributed rather than a single directory. Each authoritative operator is responsible for the zone data it serves, and delegation connects the pieces of the larger tree.
What happens when you type a website name into your browser?
Consider a request for the AAAA records of www.example.com. AAAA records provide IPv6 addresses. A typical client uses a stub resolver—the client-side component that passes the question to a recursive resolver configured by the device, network, or software.
- The client asks its recursive resolver. The stub resolver sends the DNS question to the configured resolver.
- The resolver checks what it already knows. It may have local information or a usable cached answer. If so, it can respond without contacting authoritative servers for this query.
- If needed, the resolver pursues the answer. It queries servers based on the information available to it and follows referrals toward the zone that holds the requested data. A referral points the resolver toward another server, commonly across a delegation boundary.
- An authoritative server responds. The server responsible for the relevant zone returns the requested zone data or an error.
- The recursive resolver replies to the client. It returns the result to the stub resolver and may cache it for later queries.
This is a conceptual path, not a promise that every lookup sends the same sequence of packets or starts at a root server. A resolver can forward queries to another resolver; local zones, aliases such as CNAME records, cache contents, and other DNS features can also change the path. RFC 1034 describes recursive service as returning an answer or error rather than referrals to the client: “The simplest mode for the client is recursive, since in this mode the name server acts in the role of a resolver and returns either an error or the answer, but never referrals.”
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What is a DNS resolver, and how is it different from an authoritative server?
“DNS server” is a broad, often ambiguous label. A recursive resolver and an authoritative server have different jobs, even if one software installation or operator can perform both roles.
| Role | Where it gets data | What it does for a client or resolver | Operational responsibility |
|---|---|---|---|
| Recursive resolver | Local information, cache, and queries to other DNS servers | Works on the client’s behalf to pursue resolution and return an answer or error | Resolve client queries; caching is common, but recursion and caching are distinct concepts |
| Authoritative server | Configured zone data | Answers from its zone and can refer a resolver onward at a delegation | Publish and serve authoritative data for its zones |
The distinction is about function, not necessarily physical hardware: a system can run software that fills more than one role. The terms and their current definitions are covered in the IETF’s DNS Terminology (RFC 9499), published in March 2024.
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Why does DNS use caching?
Caching lets a resolver reuse a record it recently obtained instead of repeating the upstream lookup for every client request. Each cached record has a time to live (TTL), which sets the maximum interval it may remain cached before the information should be consulted again. Once the TTL expires, the resolver needs to refresh the data through an appropriate lookup before relying on it as current.
DNS can cache negative results too: a resolver may retain information that a name or requested record was not found. That can prevent repeated upstream queries for the same unsuccessful lookup, subject to the applicable negative-caching rules.
Caching improves efficiency, but it also means that two clients—or the same client using different resolvers—may receive answers from different cache states. A change to authoritative data does not necessarily appear everywhere immediately; resolvers can keep previously retrieved data until its TTL expires.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Is DNS just a phonebook for the internet?
The phonebook analogy is useful in one narrow respect: a client can look up a name to obtain records associated with it. But a conventional phonebook suggests one central directory with direct entries. DNS instead divides data among zones, connects those zones through delegation, and has resolvers do work on clients’ behalf. A lookup may be served from cache or may require following referrals to an authoritative server.
The analogy also hides privacy considerations. A client may send a query to one configured resolver, but that does not make the lookup inherently private: resolution can involve other servers, and the resolver handling the client’s request can see its queries. The IETF discusses these risks in DNS Privacy Considerations (RFC 9076).
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