The Domain System
A Domain name
or, more properly, a fully qualified domain name, has two or more parts separated by periods, such as www.webnamesource.com
Top level domains (TLD)
are the righthandmost part of a domain name, in the case of this example webnamesource. This is what most people mean by their domain name, as this is the part that an individual or company can register for their use.
Short names are easy to remember and type, but almost all three- and four-character .com names were registered long ago, and some TLD rules do not even allow short names,(or charge extra).
In addition, there are numerous two-letter TLDs, each of which is reserved for a particular country. These include ca for Canada, us for the United States, uk for the United Kingdom, ie for Ireland, cn for China, and so on. In each case, the government of the country either runs the TLD itself or contracts it out, either with or without restrictions. Prices vary from little more than the generic TLDs to $100/year.
Most country TLDs are restricted to residents of the country or businesses that can prove they are doing business in that county. However, there are exceptions. ws (Western Samoa), to (Tonga), cc (Cocos Is.), tv (Tuvalu), and bz (Belize) are among those allowing anyone anywhere to register in their database.
Second level domains (2LD)
are the part of a domain name just before the last dot, in the case of this example com. The most ubiquitous TLDs are com, net, org, info, and biz, because all are generic and international--anyone can use domains based on them, and the price is low (at least, some places it is. Others charge far more, and sometimes offer few benefits.)
A 2LD can typically be registered for up to 10 years. Note that attempts to register someone else's trademark are doomed to failure, for the owner can get it back, and there are no refunds.
Some country domains do not allow 2LD registrations. For instance, one can register in, say, co.uk or com.cn but not directly in uk or cn. These could be called 2.5LDs.
for a given TLD is the database of all registrations under the TLD.
for one or more TLDs is an authority that is trusted to make entries into the database(s) in question and enforce the rules for the TLD(s). It takes a large initial investment to become approved as an official registrar, so most of them subcontract registrations to trusted wholesalers and retailers so as to increase volume and recoup their investment.
Registrars are selling the right to use a 2LD for a specified period and are guaranteeing that their database will connect the 2LD to a machine specified by the domain's registrant.
is the person registering the domain. Typically, the database includes not only domain names registered under the TLD, but also the name, address, phone number, and eMail address of the person registering. This information is required, and is public. Anyone registering a domain and giving false information can have the registration cancelled. Anyone who does not keep the contact information current may not receive renewal notices, and may lose the domain when it expires.
Clearly the registrant does not own the domain, (s)he merely rents its use for a specified period.
An Internet Protocol (IP) number
is an address in the form 192.168.1.1 (there may be four or six numbers, each in the range 0-256). IP numbers identify specific machines and/or functions on those machines, and the registry serves to point the fully qualified domain name toward the correct machine. Numbers are obtained separately from names, usually in large blocks, and are part of the infrastructure that most registrants need not be concerned about.
A Domain Name System (DNS) table
A given physical machine may have many functions or serve many websites. In addition, a domain may have many subdomains. At some point along the traffic route, a DNS table for the domain contains authoritative information on the exact location of the sites it directs for. Typically, the registry points to the DNS, and it in turn sends traffic to the specific address. The DNS is usually on the machine where the site itself is located (necessary if one address has many sites), but this is not always the case. For redundancy, each 2LD needs to have two DNS servers, usually names like ns3.webnamehost.net and ns4.webnamehost.net, but which a registrant must obtain from the web host and provide to the registry before the name will be connected to the address--a process that can take up to three days. Some registries require the IP numbers that go with these nameservers as well. Others do not.
Good management tools from a registrar allow the registrant extensive control over the DNS, including the ability to point traffic to another DNS elsewhere.
A Third Level Domain (3LD) or Subdomain
is the part before the penultimate period. In the example above the www part is the 3LD and is typically used to refer to a website. Since http (HyperText Transfer Protocol, used for accessing websites) has now become the most common form of traffic, most people configure things so their website also comes up if the www is omitted. Another common 3LD is ftp, for traffic using the File Transfer Protocol, commonly employed to download (get) and upload (send) files, particularly for updating one's website. Some machines require either pop or mail to be used, 3LD style when obtaining mail from the server. Others allow this to be left out.
Some people save money by buying webhosting at a subdomain under someone else's domain. WebNameHost, for instance, allows people to buy subdomain hosting under one or more domains reserved for this purpose. Hosts that do this are acting as informal registrars of the 3LD used by the customer.
Many people create additional subdomains for specialty purposes, such as parking.webnamesource.com (to which domains that have been registered but not yet connected to a website can be pointed). In this particular case, the subdomain is a website, but it is not the one at www, and it would therefore not work to use www.parking.webnamesource.com unless a fourth level domain had been defined (which can be done.)
Further information can be found in the FAQ.