The Domain Name System (DNS) is made up of a hierarchy of 5 important components:
  • Root Level
  • Top-level Domains
  • Second-level Domains
  • Sub-Domains (Third-level Domains)
  • Host
For the Domain Name System to function properly, each component of the DNS hierarchy has a server that provides answers to queries initiated by the internet users. Take for example, if an internet user is interested in browsing www.microsoft.com, the root servers will accept the request but send it to the Top-Level Domain (TLD) Name Servers, because of the Top-Level Domain name (.com). The TLD Name Server stores the IP address of the Second-level Domain (microsoft.com) within the TLD Name (.com). It will then release the IP address of the website and forward the query to the Domain Name’s Server to continue the process of bringing up the website, www.microsoft.com.
To better understand the explanations provided above, let’s look at the specific differences among the Top-level Domains, Second-level Domains, and Third-level Domains (Sub-Domains).
  • Top-level Domains (TLDs): These are the first-tier domains, and there are many of them available at the moment. TLDs are actually divided into two distinct sub-categories: They are organizational hierarchy and geographical hierarchy.
    • Organizational Hierarchy: The examples of these Top-level Domains are given below:
      DomainPurpose
      .comcommercial organizations
      .edueducational organizations
      .govgovernment institutions
      .milmilitary groups
      .netmajor network support centers
      .orgNonprofit organizations and others
      .intInternational organizations
    • Geographical Hierarchy: These are TLDs that are localized to some certain geographical areas of operations, and they are closely connected to the main TLDs. For example, .uk TLD may have (i) ac.uk for a college or other academic institutions; or (ii) .co.uk for companies or commercial entities based in the U.K.
  • Second-level Domains (SLDs): This occupies the second-tier position in the DNS hierarchy. And it is usually the main part of the domain name that indicates who owns the domain and for what purpose. For instance, “microsoft.com” is the second-level domain of the www.microsoft.com
  • Third-level Domains (Sub-domains): Sub-domains are integral parts of the main domains, but they indicate a section or department within the main or root domain. Take for instance, “microsoft.com” is the main domain, and “it.microsoft.com” is a sub-domain which tells us that the domain is about the IT department of Microsoft. Similarly, “sales.microsoft.com” is a sub-domain for the sales department.
    In conclusion, Top-Level Domain (TLD) Name Servers are a group of servers that facilitate the generation of websites’ Internet Protocol (IP) addresses. Without these servers, it would be practically difficult for Domain Name System to function properly. The provision of IP addresses, which most devices such as computers, smartphones and so on understand makes it possible to browse several websites.
    Of special note, different kinds of sub-domains can be generated based on the usefulness of the departments they are representing. Recently, for examples, there are “customercare.website.com” and “csr.website.com”, where CSR stands for Corporate Social Responsibility. The good thing about sub-domains is that they reveal exactly the duties of their departments within a larger organization.