Domain Name System (DNS)

networking dns

Definition

Def

The Domain Name System (DNS) is the distributed, hierarchical naming system that maps human-readable domain names such as example.org to resource records, most commonly IP addresses for servers on the Internet. DNS stores these mappings in zones served by authoritative name servers and answers lookup requests through recursive resolvers, so clients can locate services without knowing numeric network addresses.

Resolution modes

DNS resolution is commonly organised by who follows the delegation chain from the root of the namespace to the authoritative name server.

Iterative

Definition

Iterative DNS Resolution

Iterative DNS resolution is a DNS lookup strategy where the client, usually the local DNS resolver, queries DNS servers step by step. Each server either returns the requested record or a referral to another DNS server that is closer to the authoritative answer.

$$\text{Local DNS}\to \text{Root}\to \text{TLD}\to \text{Authoritative DNS}$$

The queried servers do not resolve the full name themselves. They only answer with the best information they have, such as “ask this next DNS server”.

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Recursive

Definition

Recursive DNS Resolution

Recursive DNS resolution is a DNS lookup strategy where the queried DNS server takes responsibility for resolving the full domain name on behalf of the client. The client sends one query and expects a final answer, such as an A record containing the IP address.

$$\text{Host}\to \text{Local DNS Resolver}$$

The resolver then performs the remaining DNS queries internally and finally returns the resolved result to the host.

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