Domain Name System
The hierarchical, distributed naming system that maps human-readable domain names to IP addresses and other network records.
Humans remember names such as gor.bio; computers need numbers such as 66.29.159.129. The Domain Name System (DNS) is the distributed database that performs this translation, and nearly every Internet service — web browsing, email, messaging, remote access — depends on it before a single byte of application data is exchanged.
DNS is hierarchical. The root zone delegates authority to top-level domains (TLDs) such as .com, .org, and .bio; each TLD delegates to the operators of second-level domains; and each domain operator publishes the records for their own names. Responsibility is split across three roles: authoritative nameservers hold the actual records for a zone; recursive resolvers (typically operated by ISPs or public services) find and cache those records on behalf of clients; and the root and TLD servers are the fixed starting points of the lookup chain.
When a client asks a resolver for www.example.com, the resolver walks the chain — root server, .com server, example.com server — or, on later queries, answers directly from its cache. Caching is essential to the design: records carry a time-to-live (TTL), and resolvers reuse cached answers until they expire, which keeps the number of queries that reach authoritative servers small.
The most common record types are:
| Type | Purpose |
|---|---|
| A | IPv4 address of a name |
| AAAA | IPv6 address of a name |
| CNAME | alias to another name |
| MX | mail server for a domain |
| TXT | arbitrary text, e.g. verification records |
| NS | authoritative nameserver for a zone |
Queries normally travel over UDP port 53, with TCP fallback for large responses and zone transfers. Because DNS answers were historically unauthenticated, attackers could forge responses; DNSSEC addresses this by signing records with cryptographic keys, allowing resolvers to verify authenticity. DNS is also a control point: providers use it to filter domains, and content delivery networks use it to steer clients to the nearest edge server. Web browsers depend on it for every HTTP request.
Tags
dns internet infrastructure networking