A Guide to Understanding Domain Names
As an aid to explaining domain names and to help you to understand them we will compare them to something everyone is already familiar with.. your house address.
If we examine a standard house address you see that it is divided into: house name/No, street address, town or city, county, country i.e. 1231, King street, Twickenham, Middlesex, UK. The address has a structure which is hierarchical starting at the top with the country. Figure 1 shows this structure.
Figure1: Structure of Typical house address
A domain name is used to identify a Website in the same way as your house address identifies your house. If we examine a fully qualified domain name (FQDN) i.e. www.juice.com in more detail then
www = name of server (physical machine)
juice.com = domain name (note: doesn't include the server name)
and juice = sub domain of com
and
com= Top level domain name
The domain name structure is a hierarchical structure just like the house address The top of the structure however is not the Country name but a dot (.). When entering a domain name into a browser it is normal to omit the dot(.). In which case it is inserted automatically by the computer.
Underneath the dot are what are known as the top level domains (TLDs) which are strictly controlled (com, net, UK) Underneath the top level domains are second level domains like IBM, Microsoft and Juice in our example.
This second level name is typically the name of an organisation and control over this name is given to that organisation, which can then divide it into third level domains etc as it wishes. At any level a domain can contain sub domains or computer names (i.e. www). The structure is shown in figure 2.
Figure 2 Domain Name system Hierarchy
As another example for those familiar with the standard file system. A domain is equivalent to a folder and a computer name equivalent to a file and a folder can contain either a file or a folder.
To completely define the location of a file you have to specify all of the folders and you write it like this c:\examples\index.htm. A FQDN is similar except we write it from bottom to top –www.juice.com.
A domain name can be considered to be a company or organisational name. The domain name doesn't include the server name .If we compare this with our house address then the domain name is equivalent to specifying an address as far as the street name but doesn't include the house number/name.
If we include the house number/name (server name) then this is called the fully qualified domain name (FQDN).
When applying for a name you apply only for the domain name (street name) and you can call the servers/hosts/websites anything we want. It is like being a property developer who builds a housing estate. He applies for the street names to the local authority and he names or numbers them as he wants.
Why is it always WWW?
If this is the case then why are all our Web servers named www? ..It is simply a convention on the internet so as to make it easier to remember the Web addresses -but they don't have to be.
You may find that some private sites deliberately choose another name for the server so as to discourage uninvited visitors. You will also find that it is possible to omit the www and still access the website. In this case the DNS system effectively inserts it for you.
Related Articles and Resources:
- Domain Names
- Choosing a domain Name- Part 1
- Choosing a domain Name- Part 2
- Top Level Domain Names
- Understanding Domain Names
- Check Domain Name Availability
- Choosing a Domain Name Registrar
- How to Register a Domain Name
- Understanding URLs
