DNS (Domain Name System)

Definition

The Domain Name System (DNS) is the internet's hierarchical naming system that translates human-readable domain names, like example.com, into the numeric IP addresses computers use to locate and connect to each other.

Overview

DNS functions as the internet's phone book: rather than remembering a server's numeric IP address, users type a memorable domain name, and DNS resolves it to the correct address behind the scenes. A DNS lookup involves a chain of servers — a recursive resolver (often run by an ISP or a public service), root servers, top-level domain (TLD) servers for extensions like `.com` or `.org`, and finally the authoritative name server for the specific domain, which holds the actual DNS records and returns the answer. DNS records come in several types serving different purposes: A records map a domain to an IPv4 address, AAAA records map to IPv6, CNAME records alias one domain name to another, MX records specify mail servers, and TXT records hold arbitrary text often used for domain verification or email security policies like SPF and DKIM. Because DNS lookups happen before almost every web request, DNS performance and reliability directly affect page load time, which is why Content Delivery Network (CDN) providers and dedicated DNS services invest heavily in fast, globally distributed, redundant DNS infrastructure. DNS is also a common attack surface: DNS spoofing, cache poisoning, and DDoS attacks against DNS infrastructure can redirect or take down traffic at scale, which is why extensions like DNSSEC (which cryptographically signs DNS responses) exist to verify that a DNS answer hasn't been tampered with in transit. Configuring DNS records correctly — pointing a domain at a server, setting up a subdomain, or verifying domain ownership for a SSL/TLS certificate — is one of the most basic but essential skills in deploying anything on the web. It is often mentioned alongside HTTP/2 in this space.

Specification

• Translates human-readable domain names into numeric IP addresses
• Hierarchical lookup chain: recursive resolver, root, TLD, authoritative servers
• Multiple record types — A, AAAA, CNAME, MX, TXT — for different purposes
• Caching at multiple levels to speed up repeated lookups
• DNSSEC extension for cryptographically verifying DNS responses
• Critical infrastructure often targeted by spoofing and DDoS attacks

Use Cases

History

The Domain Name System was invented in 1983 by Paul Mockapetris, at the request of Jon Postel, to replace the early Internet's single, centrally maintained HOSTS.TXT file with a distributed, hierarchical, and dynamic database mapping names to addresses. Mockapetris authored the original specifications, RFC 882 and RFC 883, in 1983, and wrote the first DNS server implementation, called "Jeeves." Those documents were superseded in November 1987 by RFC 1034 ("Domain Names — Concepts and Facilities") and RFC 1035 ("Domain Names — Implementation and Specification"), which remain the foundation on which all DNS implementations are built. DNS's delegated, hierarchical design is a large part of why the Internet's naming system scaled to billions of hosts.

Frequently Asked Questions

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