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Domain Name System (DNS)

The Domain Name System is the distributed naming system that connects domain names with internet resources such as servers, email systems, and other services.

The Domain Name System, or DNS, is the distributed naming system used to connect domain names with internet resources.

Its best-known function is translating a human-readable domain name into information computers can use to locate the relevant service.

ICANN describes DNS as the system that connects domain names to their associated internet addresses. ICANN's DNS overview

MDN describes DNS as a hierarchical, decentralized naming system for internet-connected resources. MDN's DNS glossary

What DNS Does

Suppose someone visits:

example.com

Their browser ultimately needs to know where requests for that hostname should go.

DNS can provide information such as:

  • IP address
  • Mail servers
  • Verification values
  • Service locations
  • Delegated nameservers

Different DNS Record types represent different information.

DNS Is More Than Website Routing

DNS can affect:

  • Website traffic
  • Email
  • Subdomains
  • Domain verification
  • Third-party services
  • APIs
  • Email-security configuration
  • CDN routing

Changing DNS therefore deserves more care than simply:

“Point the domain at the new website.”

How Resolution Works

A simplified lookup may involve:

Browser
   ↓
DNS resolver
   ↓
DNS hierarchy
   ↓
Authoritative nameserver
   ↓
DNS record
   ↓
Destination

The authoritative Nameserver provides the definitive records for the domain's DNS zone.

Why It Matters

A perfectly healthy website can be unreachable if DNS points somewhere else.

Likewise, changing website DNS incorrectly can affect unrelated services such as email.

This makes DNS one of the most important systems to document before migrations.

Common Problems

Common problems include:

  • Wrong A record
  • Missing CNAME
  • Incorrect nameservers
  • Email records removed
  • Old DNS provider still assumed to be active
  • Records copied incompletely
  • TTL misunderstood
  • DNSSEC misconfigured
  • Several people editing DNS without documentation

How to Improve

Treat DNS as production infrastructure.

Before changing records:

  • Understand what the record does
  • Record the previous value
  • Check TTL
  • Identify services depending on the hostname
  • Verify the new value
  • Plan rollback where appropriate