DNS refresher

A refresher on DNS

Domain name anatomy

Domain name

A string of text that maps to a numeric IP address. Domain names are typically broken up into two or three parts separated by dots.

Examples: “namebase.io”, “coinbase.com”, “learn.namebase.io”, “turbomaze/”, “.com”

Top-Level Domain (TLD)

The right-most section of a domain name (often referred to as the “extension”), identifying the general namespace that a domain name is part of.

Examples: “.com”, “.net”, “.org”, “.io”

Second-Level Domain (SLD)

The section of the domain name immediately to the left of the TLD. Also referred to as the “apex domain”, but often misnamed as the "subdomain". This typically identifies specific company or organization the domain name belongs to.

Examples: “namebase” is the SLD in “namebase.io”, “google” is the SLD in “google.com” and “mail.google.com”

Third-Level Domain or Subdomain

The section of the domain name to the left of the SLD.

Examples: “learn” is the subdomain in “learn.namebase.io”, “mail” is the subdomain in “mail.namebase.io”

Root zone

At the top of the DNS hierarchy is a file called the root zone where TLD ownership info is recorded. The root zone is managed by the ICANN, which determines who gets what TLD — "who" in this case means governments, non-profits, and for-profit corporations like Verisign which owns ".com". In other words, the entire traditional DNS system is controlled at the top by a single entity, ICANN.

Root server

What's a root server?


What are nameservers?


What's a resolver?


What's a registrar?


What's a registry?