What is DNS?

The Domain Name System is a distributed, hierarchical database and query protocol. It lets clients retrieve typed information associated with names, including addresses, mail routing, authoritative servers, service data, and verification records.

Names and Resource Records

DNS does more than translate one hostname into one IP address. An A record holds an IPv4 address, AAAA an IPv6 address, MX mail-routing data, NS authoritative server names, and many other types carry different data. One name can have several records or no address record at all.

Hierarchical Names

A fully qualified domain name identifies a path in the DNS tree. In www.example.com., the final dot represents the root, com is below it, example is below com, and www is a name within that domain. The trailing dot is often omitted in user interfaces but matters when distinguishing absolute from locally relative names in configuration.

Distributed Authority

DNS authority is delegated down the hierarchy. Root servers direct resolvers toward top-level-domain servers, which direct them toward authoritative servers for delegated zones. Organizations manage their own authoritative data without storing the entire global namespace on one central server.

Resolution and Caching

A host's stub resolver usually sends a query to a recursive resolver. That resolver can answer from valid cache or query the hierarchy on the client's behalf. Record TTLs limit how long cache entries can normally be reused, improving scale but delaying visibility of changes until caches refresh.

DNS success does not prove route, transport, TLS, or application health. DNS failure can also arise before any external query because /etc/hosts, search suffixes, local caches, or name-service policy affect the system resolver.

Summary

You can now describe DNS as a typed, cached, hierarchical data system.

1. Distinguish DNS resource-record types by purpose.
2. Read a fully qualified name from the root downward.
3. Identify delegation and authoritative responsibility.
4. Separate name resolution from application connectivity.