Host Names and Domain Names

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Domain is a section of the internet operated by a single authority, such as a university or a business.

• internet is based on domains

Domain names are the familiar, easy-to-read names that are used to navigate the internet.

• easier for humans to remember than IP addresses
• E.g. google.com
• Every domain must be registered with ICANN

Structure

• Internet Protocol (IP) uses a binary address value to locate a host on an internetwork
  • formatted in:
    • dotted decimal (IPv4)
    • or hex (IPv6) notation
  • not easy to remember or input correctly
• a “friendly” name is also typically assigned to each host
  • 2 kinds:
    • host name
      • is configured when the OS is installed
      • must be unique on the local network
    • fully qualified domain name (FQDN)
      • used to avoid duplicate host names on the Internet
      • provides a unique identity for the host belonging to a particular network
      • made up of the host name + domain suffix

Example

nut.widget.example.

• host name is nut
• the domain suffix consists of:
  • the domain name widget
  • and top-level domain (TLD) .example
• could include subdomains between host and domain name
• trailing dot represents the root of the hierarchy

Important

• when configuring name records, an FQDN must include the trailing period to represent the root
  • can be omitted in most other cases

Domain Registrar

• domain name must be registered with a registrar to ensure it is unique within a TLD
  • once registered, cannot be used by others
  • same domain name can be registered with different TLDs as distinct
• multiple hosts can exist within a single domain
  • but FQDNs must follow certain rules:
    • host name must be unique within the domain
    • total length of an FQDN cannot exceed 253 characters
      • each label (part defined by a period) cannot exceed 63 characters excluding .
    • DNS label should use letter, digit, and hyphen characters only
      • label should not start with a hyphen
      • punctuation characters should not be used
    • DNS labels are not case-sensitive
• internet registries may have their own restrictions