Domain Hierarchy
Last updated
Last updated
Domain hierarchy refers to the structured, layered organization of domain names within the Domain Name System (DNS). It breaks down domain names into different levels, starting from the most general (root) to the most specific (subdomains). This hierarchy is read from right to left in a domain name.
The topmost level of the hierarchy, often represented by an implicit dot at the end of a domain name. It doesn’t appear in URLs but is the starting point for DNS resolution.
This is the first visible layer after the root and is the rightmost part of a domain name, such as:
Generic TLDs (gTLDs): .com, .org, .net, etc., which are used for general purposes and not restricted to specific countries.
Country Code TLDs (ccTLDs): .uk, .jp, .us, etc., which are used to represent specific countries or territories.
The Second-Level Domain (SLD) is the part of the domain name immediately before the TLD, representing the main label for a website. Organizations and individuals register SLDs relevant to their brand or purpose, such as example.comor amazon.co.uk. SLDs are typically limited to 63 characters.
Subdomains are labels added to the front of a domain name, sitting on the left side of the SLD. They allow website owners to create separate sections within their main domain, such as blog.example.com or shop.google.com. Subdomains follow the same creation restrictions as SLDs, including character limits, and are separated by periods from the main domain.
Here, we will talk about - What is the difference between a third-level domain and a subdomain? For example, in x.y.z.com, how would the components be broken down?
In the domain x.y.z.com, the third-level domain and subdomain are essentially the same concept, though they are often described differently depending on the context.
.com
TLD
This is the highest level in the domain hierarchy, indicating the category or type of domain, such as .com, .org, or a country-specific TLD like .uk.
z
SLD
This is the main domain name registered under the TLD. In this case, z is the second-level domain, which could represent a company or website.
y
Third-Level Domain
This is the next level after the second-level domain. Here, y is considered the third-level domain because it is directly under the second-level domain (z.com).
x
Fourth-Level Domain
This is an additional subdomain under the third-level domain (y.z.com). The term "subdomain" is generally used to refer to any domain name that is part of a higher-level domain.
Third-Level Domain: Refers specifically to the domain that comes after the second-level domain (e.g., y in y.z.com). It’s part of the domain hierarchy and is counted from the right.
Subdomain: A broader term that refers to any domain that exists under a higher-level domain. In x.y.z.com, both x and y are subdomains of z.com, but y is also specifically the third-level domain.
In short, all third-level domains are subdomains, but not all subdomains are third-level domains. Subdomains can go beyond three levels (like x.y.z.com) and still be called subdomains.
Note: The maximum length of a domain name, including the TLD, is 253 characters. This includes the total length of the domain name and all its labels (e.g., subdomain.example.com). Each label within the domain name can be up to 63 characters long.
