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A domain name resolver is software that obtains DNS information for a requested domain name and record type. It may answer using information it already has or consult other DNS servers to find the answer. In a typical lookup, a client-side stub resolver sends the request to a recursive resolver, which may consult authoritative name servers.
What does a domain name resolver do?
A resolver handles a request for information associated with a domain name, such as a particular DNS record. It returns the requested information or a DNS response explaining why it could not be obtained.
RFC 9499, the IETF’s 2024 terminology reference, reproduces RFC 1034’s description: “The resolver is located on the same machine as the program that requests the resolver’s services, but it may need to consult name servers on other hosts.” That means a resolver is a software function, not inherently a physical device.
How does a DNS lookup move from a device to an answer?
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A program or device needs DNS information for a domain name and record type.
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A client-side stub resolver sends the request to a recursive resolver. The exact component boundaries vary between implementations and deployments.
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The recursive resolver may return information from its local cache. If it does not already have an answer, it can query other DNS servers to obtain one.
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An authoritative name server can provide data for the zone it serves. A resolver may consult authoritative servers or other servers as needed, then return an answer or an error to the requester.
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DNS exchanges can also use iterative behavior: a server may return a referral to another server, leaving the requester or resolver to pursue the next step. RFC 1035 describes a resolver asking a known name server and receiving either the desired information or a referral.
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What is the difference between stub and recursive resolvers?
| Role | What it does |
|---|---|
| Stub resolver | A resolver that cannot perform all resolution itself and generally relies on a recursive resolver. It commonly acts as the client-side component that forwards a request. |
| Recursive resolver | A resolver operating in recursive mode. It can answer from local information or query other servers to obtain an answer or error for the original request. |
Recursive resolvers are generally expected to cache responses, but caching is not part of the definition: RFC 9499 notes that some recursive resolvers may not cache.
Is a resolver the same as a DNS server?
No. “DNS server” is often used broadly for a system that participates in DNS, while “resolver” describes the function of obtaining DNS information for a request. An authoritative name server holds data for its zone and answers from that data; a resolver obtains information, often by consulting other servers. These are distinct roles, although DNS software or a system can combine them.
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The word “resolver” is also context-dependent. It may mean a stub resolver or a recursive resolver, so identifying which role is meant makes descriptions of a DNS setup clearer.
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When recursion is requested and available, a server uses its resolver function to pursue the lookup and returns an answer or an error rather than a referral, as described in RFC 1034. In an iterative exchange, by contrast, a server can refer the requester to another name server rather than completing the lookup on its behalf.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Which standards define DNS resolvers?
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RFC 9499, published in 2024, provides terminology for resolvers, stub resolvers, recursive mode, and recursive resolvers.
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RFC 1035, published in November 1987, describes DNS implementation, including resolvers querying known name servers and following referrals.
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RFC 1034, published in November 1987, sets out DNS concepts, including recursive query behavior.
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