You are probably used to seeing Internet addresses that look like these
http://www.paranoidagnostic.net/category/sysadmin
cloned.milkmen@paranoidagnostic.net
The first is called a URL and is used for web pages, and the second is an email address. While these addresses both look quite different and are used for different purposes they both contain something called a Domain Name (or DNS name). In this case the domain name is “paranoidagnostic.net”.
Domain names are used to organize Internet addresses in an orderly way and to delegate authority for the creation of Internet addresses.
Top-level Domains
Internet domain names are organized according to a hierarchy. Levels in the hierarchy are denoted by periods in the domain name. When you read a domain name from left to right, the left is the lowest level and the right is the top-most level of the hierarchy. The lower levels are referred to as subdomains of the higher level domains./p>
For example, the DNS name “www.paranoidagnostic.net” shows three levels of the hierarchy:
- net is called the top-level domain
- paranoidagnostic is a subdomain of net
- www is a subdomain of paranoidagnostic.net
The top-level domains (TLDs) are very important. There are only a limited number of top-level domains and they are controlled by various authorities around the world. There are generally three types of top-level domains: US-only, country specific, and generic.
US-only TLDs are only available to US institutions and are under tight control. For example, “mil” is only for the US military, “gov” is only for the US government, and “edu” is only for accredited US post-secondary institutions.
Country-specific TLDs have two letter codes that usually (but not always) correspond to international standard two-letter codes for those countries. For example, the TLD for Canada is “ca” and the TLD for the United Kingdom is “uk”.
generic TLDs are usually available to anyone in the world. “com”, “net”, “org”, “biz”, “info” and a growing list of others are in this category.
Who can have a domain? How do you get one?
TLDs are created by the Internet Corporation for Assigned Names and Numbers (ICANN). Regular organizations cannot have TLDs. Individual people or organizations can obtain subdomains of TLDs. ICANN assigns a separate authority to govern each TLD and those authorities set their own rules about who can and cannot have a subdomain.
For example, the “UK” TLD is governed by Nominet. Nominet administers all UK subdomains and sets rules for how they can be named. In the UK TLD commercial organizations are put in a further subdomain of “.co.uk” and educational institutions in “sch.uk”. For example, a phone company in the UK could get a domain of “myphonecompany.co.uk” but not “myphonecompany.uk” or “myphonecompany.sch.uk”. In the UK authority for some domains is delegated to an organization other than Nominet. For example, subdomains of “parliament.uk” have their own system of rules.
Contrast that with the “CA” TLD. “CA” is governed by an organization called the Canadian Internet Registry Authority (CIRA). It does not have a special subdomain for commercial organizations. A phone company in Canada could obtain “myphonecompany.ca” for a domain name. Similar to the UK TLD government subdomains are restricted. Only the Canadian Federal Government can obtain subdomains of “gc.ca”.
Some countries have turned over control of their TLDs to commercial companies that allow anyone in the world to use them. For example “TV”, “FM”, and “AD” are all country-specific TLDs that are administered by commercial organization that treat them like generic TLDs.
Finding TLD Authorities an Policies
It is often very helpful to know who governs a TLD and what their policies are. For example, if you find a website might appear to be for a institution in a specific country and have a subdomain that appears from that country. In the UK and Canada (”.ca”) you could be sure that any site that ends in “.parliament.uk” or “.gc.ca” are associated with the government. But a website in other subdomains may not be authentic. Each country has its own authority and own rules so verifying who is real and who is not can be challenging.
Fortunately, the Internet Assigned Numbers Authority (IANA) keeps a list of all of the TLD authorities. You can find the contact information, usually including website addresses, for every TLD on that list. You can then contact the listed authority to find out what their policies are.
Notes
Note: The Internet’s domain name system is referred to as DNS (Domain Name System) and defined by many RFCs (Internet standards).
