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.

CheckWhy is DNS more than a hostname-to-address list?

It permanently assigns MAC addresses to every Ethernet frame. It stores typed records for several kinds of service and delegation data. It guarantees that every named application is healthy.

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.

CheckWhat does the final dot in www.example.com. represent?

The DNS root and an absolute name. A wildcard for every top-level domain. An instruction to use only IPv4.

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.

CheckWho provides definitive data for a delegated DNS zone?

Any browser that previously visited the site. The zone's configured authoritative name servers. Every router carrying a packet to the address.

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.

CheckWhat does a DNS record TTL primarily control?

How many routers an IP packet may cross. How long the application must remain healthy. How long a resolver may cache the record under normal rules.

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.