Domain names are classified into the following levels:
- Root domain: . (a dot)
- Top-level domain: for example, .com, .net, .org, and .cn
- Second-level domain: subdomain names of the top-level domain names, such as example.com, example.net, and example.org
- Third-level domain: subdomain names of the second-level domain names, such as abc.example.com, abc.example.net, and abc.example.org
- The next level domain names are similarly expanded by adding prefixes on the left of the previous-level domain names.
- A domain name is segmented using dots (.).
- Each label can contain letters, digits, and hyphens (-) and cannot start or end with a hyphen.
- A domain name label cannot exceed 63 characters.
- A domain name is not case-sensitive and does not exceed 254 characters, including the dot added at the end by default.