Domain Name Extensions
This article discusses domain name extensions and why it's important to pick the right extension when selecting a domain name.
You may also like to read the Domain Name Extensions Definitions, which lists each extension and what it is used for.
What Is A Domain Name Extension?
A domain name extension is the last part of a domain name. It is the part that follows the "name" part of your domain.
For example, in the domain name
quackit.com the domain extension is
Domain Name Extension vs Top-Level Domain
A top-level domain is the part that comes after the final dot (for example,
Domain extensions, on the other hand, is anything that follows your chosen name (for example
Often a domain name extension is simply the top-level domain, but this isn't always the case. Some domain extensions include more than just the top-level domain - they also contain a country code second-level domain (ccSLD) which precedes the top-level domain (for example
Here's an example to demonstrate what I mean:
myth.CO.NZ← Domain extension is highlighted
myth.co.NZ← Top-level domain is highlighted
myth.CO.nz← Country code second-level domain highlighted
In this example,
.co.nz is the domain extension used for companies based in New Zealand.
Here's a breakdown of the domain extension:
- Domain name extension:
- Top-level domain:
- Country code second-level domain:
In this case, the ccSLD indicates that it is a company. If it was an organization, the ccSLD would be
.org and the full extension would be
.org.nz. Note that both cases (
.org.nz), the top-level domain would be
Restricted Domain Extensions
Some domain name extensions have restrictions on who can register them.
Sponsored Top-Level Domains (sTLD) such as .AERO and .GOV are sponsored by private agencies or organizations that establish and enforce rules restricting the eligibility to use the top-level domain.
Generic-Restricted Top-Level Domains such as .BIZ and .PRO are intended to be restricted and ascertained more stringently than generic top-level domains.
Many country code domains have restrictions too. Typically, you need to be an entity from that country before you can register a name.
For example, to register a
.com.au domain name, you must be:
- an Australian registered company; or
- trading under a registered business name in any Australian State or Territory; or
- an Australian partnership or sole trader;
- a foreign company licensed to trade in Australia; or
- an owner of an Australian Registered Trade Mark; or
- an applicant for an Australian Registered Trade Mark; or
- an association incorporated in any Australian State or Territory; or
- an Australian commercial statutory body.
Not all domain name extensions are created equal!
If your domain extension is not recognized by the Internet Corporation for Assigned Names and Numbers (ICANN) and/or your national authority, you could run into problems later on.
.com.au example is an internationally and nationally recognized domain extension. The top-level domain (
.au) is internationally recognized by ICANN, and the second-level country code (
.com) has been implemented by auDA, the Australian Domain Name Administrator (as formally endorsed by the Australian Government).
Some domain name extensions being offered on the Internet are not properly recognized as such. This is particularly true for the so-called "free domain names".
For example, at first glance, the domain extension
.uk.co might appear to be the domain extension for UK based companies. But it is not.
The correct extension for UK based companies is
.co.uk because the top-level domain (
.uk) is reserved for the UK (as specified by ICANN).
While the top-level domain
.co is a recognized top-level domain, it is actually intended for Colombia.
Unless you understand this, you could be sold a domain name that is at risk of disappearing. In fact, this is exactly what happened to those who registered domains under the
.uk.co extension - they lost their domain names!
Until 16 February 2003, a company called Net Registrar was offering "domain names" with the
uk.co extension. But then the Columbian government took over administration of the
.co top-level domain. The result was that all customers with a
.uk.co lost their "domain names" (which were really only sub-domains anyway).
How did this happen?
Net Register was simply a company who chose to register
uk.co as a domain name. Therefore, the
uk part of the domain wasn't actually part of the extension. As with anyone who has a domain name, they could set up sub-domains (i.e.
Most companies use sub-domains for different parts of their own corporate website. Net Register chose to use sub-domains for customers, but offered them as "domain names" (for example
Unfortunately, most customers wouldn't have known the difference between a domain name and a sub-domain. What these customers didn't realize was that, by registering
theirdomain.uk.co, they were only registering a sub-domain of the
uk.com domain name.
So, when the Columbian government took over administration of the
.co top-level domain, all customers lost their domain names!
Choose an ICANN Recognized Domain Name
So, how can I prevent this from happening to me?
Before you register a domain name, check that the top-level domain is recognized by ICANN and that its country code second-level domain is correct. You can check your domain extension here.
Alternatively, you can go straight to ZappyHost to register an ICANN recognized domain name.