Domain Name Server (DNS)

  • Each computer in a TCP/IP network is uniquely identified by its IP address.

  • So when a user wants to access another computer they have to know the IP address of that computer. It is hard to remember every IP you need.

  • Hence, domain names are mapped to IPs.

  • So is a domain name, which is mapped to the IP address of GitHub Pages. When you go to, you get a GitHub webserver’s IP and when you request a page, it serves the content you’re seeing now.

Each domain name ends with a suffix

  • A suffix represents a TLD (top level domain)
  • .com,, .org are common tlds, but many exist
  • Some domains

Domain levels

  • right at the top
Top-level examples

uk, com, edu

2nd level domains

gov, co,nhs

3rd level (TLDs)

data, education, amazon

They are arranged hierarchically.

For instance

ocr is the domain name org is the second level domain and uk is the top level domain

Fully-qualified Domain Names (FQDN)

  • The website domain name along with the host server name is called a fully qualified domain name
  • www, mail and ftp are some examples of host server names. (any subdomain)
  • Root
    • .
  • TLD
    • com
  • Domain
    • ionos
  • Hostname
    • www

Internet Registrars

  • The companies that hold domain name rights and can register a domain for you
  • Registrars are accredited by a governing entity
  • Internet registrars are responsible for storing the details of domain names along with the companies they are registered to.

Transport over the internet