【My Study Note】Anatomy of a Domain Name
Anatomy of a Domain Name
Any given domain name has three primary parts, and they all serve specific purposes.
Let’s take the domain name “www.google.com”, the three part here should be pretty easy to spot since they’re each set off from each other by a period.
They’re www, google, and com, the last part of a domain name is known as the TLD (Top Level Domain). In this case, it’s the .com portion of the domain name.
TLD (Top Level Domain)
There are only a certain restricted number of defined TLDs available, although that number has been growing a lot in recent years. The most common TLDs are ones you’re probably already familiar with .com, .net, .edu and so on.
You’ve probably also seen some country specific TLDs such as .de for Germany or .cn for China. Due to the growth of the Internet, many of the TLDs originally defined have become very crowded.
So today, a number of vanity TLDs are available, everything from .museum to .pizza. Administration and definition of TLDs are handled by a non-profit organization known as ICANN (the Internet Corporation for Assigned Names and Numbers).
ICANN
ICANN is a sister organization to the IANA, and together they help define and control both the global IP spaces, along with the global DNS system.
Domain Name
A domain is the name commonly used to refer to the second part of a domain name, which would be, google in our example.
Domains are used to demarcate where control moves from a TLD name server, to an authoritative name server. This is typically under the control of an independent organization, or someone outside of ICANN. Domains can be registered and chosen by any individual or company, but they must all end in one of the predefined TLDs.
subdomain
That www portion of this is known as the subdomain, sometimes referred to as a host name if it’s been assigned to only one host.
When you combine all these parts together, you have what’s known as a FQDN (Fully Qualified Domain Name).
While it costs money to officially register a domain with a registrar, subdomains can be freely chosen and assigned by anyone who controls such a registered domain.
Technically you can have lots of subdomain names, for example host.sub.sub.subdomain.domain.com can be completely valid. Although you rarely see fully qualified domain names with that many levels. DNS can technically support up to 127 levels of domain in total for a single fully qualified domain name.
There are some other restrictions in place for how your domain name can be specified. Each individual section can only be 63 characters long and a complete FQDN is limited to a total of 255 characters.