Simple definition
DNS lets you use easy-to-remember names, such as boiteaoutilsinformatique.fr, instead of entering a server’s IP address directly.
Technical definition
The Domain Name System is a distributed, hierarchical naming system. Resolvers query DNS servers for records such as A, AAAA, CNAME, MX or TXT and temporarily cache the answers.
What is it used for?
DNS is used to find a website’s address, locate a mail server, or allow computers in a Windows domain to discover domain controllers and other services.
Practical example
Before opening a website over HTTPS, a browser resolves the site’s domain name to an IP address and then connects to the corresponding server.
Common issues
- DNS server unavailable
- Missing or incorrect DNS record
- Stale answer stored in cache
- Propagation delay after a DNS change
Related terms
IP address · DHCP · SMTP · SPF · DKIM · DMARC
Key point: DNS behavior depends on the resolver, authoritative servers, caching and the records configured for the domain.