Domain Name Structure Overview

Overview

This lecture explains the structure of domain names, the roles of various components, and the organizations managing them.

A domain name consists of three main parts: subdomain, domain, and top-level domain (TLD).
Example: In www.google.com, "www" is the subdomain, "google" is the domain, and "com" is the TLD.
The subdomain (e.g., www) can be freely chosen by the domain controller.
A subdomain is sometimes called a host name if linked to one host.

TLD is the last part of a domain name, such as .com, .net, or .edu.
There are both generic TLDs (e.g., .com, .net) and country-specific TLDs (e.g., .de, .cn).
Vanity TLDs like .museum and .pizza are now available due to internet growth.
Administration and definition of TLDs are managed by ICANN.

Domains are the second part of a domain name (e.g., "google") and are controlled outside of ICANN after registration.
Domains can be registered by individuals or companies, but must end in an approved TLD.
A registrar is a company authorized by ICANN to sell unregistered domains.
Subdomains can be nested in many levels (e.g., host.sub.sub.domain.com).

Fully Qualified Domain Name (FQDN) includes all domain parts.
DNS allows up to 127 domain levels within a single FQDN.
Each domain section can be up to 63 characters; total FQDN length is limited to 255 characters.

TLD (Top-Level Domain) — The last segment of a domain name (e.g., .com).
Domain — The second part of a domain name, marking transfer of control to an organization or individual.
Subdomain — The portion before the domain, which can be assigned freely by the domain owner.
FQDN (Fully Qualified Domain Name) — The complete domain name, including all domain levels.
Registrar — A company authorized by ICANN to register domains.
ICANN — Internet Corporation for Assigned Names and Numbers, oversees TLDs and global DNS.