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DNS name resolution is the process of looking up DNS records for a name, such as a website’s domain. Usually, a device’s stub resolver sends a query to a recursive resolver. That resolver may answer from its cache or consult authoritative name servers, then returns a record or an error.
What DNS name resolution means
DNS resolution is a distributed lookup, not a search of one central database. DNS records are organized into zones and served by name servers. A resolver starts with information about a name server and can either obtain the requested data or receive a referral to another server that is responsible for a closer part of the DNS tree. RFC 1034 describes this distributed model.
In a typical lookup, the device does not contact every DNS server itself. Client-side software called a stub resolver sends a query to an upstream recursive resolver. That resolver handles the work needed to obtain an answer. An authoritative server holds the DNS data for a zone and answers queries about it. These roles are defined in RFC 9199.
How a domain name is resolved
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The client sends a query. The stub resolver asks an upstream recursive resolver for a particular record type associated with a name.
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The recursive resolver checks available data. It can answer using data already in its cache. If it has no usable answer, it queries DNS servers and follows referrals toward the servers responsible for the name.
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An authoritative server responds. A server authoritative for the relevant zone can provide the requested record. A server that is not responsible for the needed data may refer the resolver to another server.
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The resolver replies to the client. The response can contain the requested data, aliases encountered along the way, or an error. The client then uses the result as appropriate.
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The recursive resolver’s work is often iterative: it follows referrals from one server to another until it has an answer or an error to return. The client’s request for recursive service and the resolver’s iterative queries are different parts of the process. RFC 1034 and RFC 9199 describe this interaction.
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Recursive and iterative queries are different
With a recursive query, the client asks the server to pursue the lookup and return an answer or an error, rather than passing a referral back for the client to follow. A non-recursive response may instead provide data the server already has, an error, or a referral to another server.
In DNS messages, the RD bit requests recursive service. The RA bit indicates that the server is willing to provide it; RA alone does not prove that recursion was performed. RFC 1034 says a client can check that both RD and RA are set in the reply to verify recursive mode. Read RFC 1034.
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Why DNS answers may be cached
A resolver can keep DNS data it has obtained and reuse it for later queries. This avoids repeating non-local lookups and can make repeat retrieval more efficient. Cached records have a time to live (TTL); when the TTL expires, the cached data is discarded.
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Resolvers can also cache negative results, such as a response indicating that a name or requested data was not found. A DNS change may therefore not appear to every resolver at once: a resolver can continue using relevant cached positive or negative information until its TTL expires. There is no single universal propagation duration; it depends on the cached data and its lifetime. RFC 1034 and RFC 1035 cover DNS caching and responses.
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A lookup may encounter a CNAME record, which identifies an alias for another name. There can be one or more aliases before the resolver reaches the data requested by the client.
Not every failed lookup means the same thing. The queried name might not exist, the name might exist but lack the requested record type, or a server problem might prevent a successful response. DNS distinguishes name errors from cases where requested data is absent, even if an application presents them in a similar way. The protocol also defines temporary and format-related response codes. RFC 1034 and RFC 1035 describe these distinctions.
What DNS over HTTPS changes
DNS over HTTPS (DoH) carries DNS queries and responses in HTTPS exchanges. It changes the transport between a client and its selected resolver, not the basic purpose of DNS resolution. RFC 8484 specifies that the HTTPS channel provides integrity and confidentiality between those endpoints. RFC 8484.
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The client’s configuration determines which DoH server it uses, and resolver choice can influence the results it receives. There is also a bootstrap dependency: a client cannot use a DoH server to perform the initial DNS lookup of that same server’s hostname. DoH therefore changes how a query travels and which resolver receives it; it does not remove the need to find DNS records. RFC 8484.
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