DNS
DNS is the internet's distributed naming system that resolves human-readable domain names into IP addresses through a hierarchy of servers.
DNS, the Domain Name System, is the distributed directory of the internet. It maps human-friendly domain names, such as example.com, to the numeric IP addresses that computers use to find each other.
How It Works
DNS is a hierarchical, distributed database. When an application needs to resolve a name, a resolver queries a chain of servers: root servers point to top-level domain servers (such as .com), which point to the authoritative servers for the specific domain, which return the answer. Resolvers and clients cache results for a duration set by each record's time to live (TTL), so repeated lookups are fast.
DNS stores several record types. A and AAAA records hold IPv4 and IPv6 addresses, CNAME records alias one name to another, MX records direct email, and TXT records carry arbitrary text used for verification and policy. Queries traditionally travel over UDP for speed, falling back to TCP for large responses, with encrypted variants like DNS over HTTPS adding privacy.
Why It Matters
Almost every internet interaction begins with a DNS lookup, so DNS is critical infrastructure. It also enables flexibility: services can change servers or IP addresses without changing the names users know. DNS-based routing supports load balancing, failover, and steering users to the nearest CDN edge.
The trade-offs center on caching and propagation. TTLs balance freshness against performance, and changes can take time to spread. Because DNS is foundational, outages and misconfigurations are highly visible and security hardening, such as DNSSEC, matters.
Related Terms
DNS queries use UDP and TCP, steer traffic to CDNs, and precede TLS handshakes in establishing connections.