Source
Domain Name System
Background material for the terms, structure and process of resolution.
DNS is a hierarchical distributed naming system that maps domain names to IP addresses and delegates responsibility along the domain tree through authoritative DNS servers.
Hierarchy of DNS servers
The DNS namespace is a tree: root → TLD → domain. Each zone is served by authoritative servers, and a recursive resolver caches responses.
DNS server hierarchy
Select a level to highlight its role in the system
Recursive Resolver
Caching and recursive queries
Root Name Servers
Delegation to TLD
TLD Name Servers
.com, .org, .ru, etc.
Authoritative Servers
Domain zone records
Interactive resolve process
A recursive resolver goes through the hierarchy of DNS servers, receives references to authoritative servers and returns a response to the client, storing it in the cache.
Domain name resolution
Click a step or use the controls to play through the sequence
Active Step
Click "Start" to run the domain name resolution flow.
Cache
Responses are cached by the resolver and client to reduce latency of subsequent queries.
What is important to remember
Caching and TTL
Recursive resolvers and clients cache entries, reducing the load on authoritative servers.
Zones and delegation
Root and TLD servers are not responsible for specific domains, but direct the request to the zones below.