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The domain name to IP resolution process – Part II/IV – DOMAIN NAMES

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Published on: May 25, 2010 by Arnold Pablo

The domain name to IP resolution process – Part II/IV – DOMAIN NAMES


Before I go on to the query process, I would like to present a small briefing about Domain Names basics :

The Domain Name System uses a tree (or hierarchical) name structure. At the top of the tree is the root node followed by the Top-Level Domains (TLDs), then the Second-Level Domains (SLD) and any number of lower levels, each separated with a dot. TLDs are split into two types:

1. Generic Top-Level Domains (gTLD): For example, .com, .edu, .net, .org, .mil, etc.

2. Country Code Top-Level Domains (ccTLD): For example, .us, .ca, .tv, .uk, etc.

For instance abc.com, is actually a combination of an SLD name and a TLD name and is written from left to right with the lowest level in the hierarchy on the left and the highest level on the right:


The term Second-Level Domain is technically precise in that it defines nodes at the second level within the domain name hierarchy. There are also Third-Level Domains, which are especially relevant with ccTLDS. Any name just which is to exist in the Internet’s name space just to the left of the gTLD or ccTLD ( i.e. SLD ) should be brought from an Accredited Registrar or simply, Registrar.

So what is www.abc.com?

From our reading previously on domain names basics, we can see that if we assume a domain name www.abc.com, is built up from www and abc.com. The domain name abc.com part was delegated from a gTLD registrar, which in turn was delegated from ICANN. The owner of the domain chose the www part since they are now the delegated authority for the abc.com domain name. They own everything to the left of the delegated domain name, in this case abc.com *. The leftmost part, the www in this case, is called a host name. Keep in mind that only by convention do web sites use the host name www (for World Wide Web), but a web site can be named efg.abc.com—few may think of typing this into their web browser, but that does not invalidate the name! Every computer that is connected to the Internet or an internal network and is accessed using a name server has a host name.

Consider some examples:

www.abc.com  a company web server

ftp.abc.com  a company file transfer protocol server

pc17.abc.com  a normal PC

A host name must be unique within the delegated domain name, but can be anything the owner of abc.com wants. Say, he can make ftp.abc.com as the web server. There is no protocol or convention to name web servers starting with www. It is usually given for better understanding that the name starting with www will be the web server and that starting with ftp will be the ftp server.

One more thing to note is that q1.abc.com & q2.abc.com need not be 2 different hosts (separate machines). It can also be 2 different sub-domains of abc.com on the same host!

To summarize: the owner can delegate, in any way they want, anything to the left of the domain name they own (or were delegated). The delegated owner is also responsible for administering this delegation.

* For .name TLD, the registry handling it, Verisign Inc., places some restrictions regarding the registration of third level domain names and it’s ownership. You may find further details on it at :


Category : Linux, Training

Arnold Pablo

Arnold Pablo

Technology always fascinated me and continues to do so. I started my career back in 2004 as a Junior System Admin and worked in various capacities both in technical and managerial roles. I love to experiment and try out new OSS projects and in free time, go for cycling to the interiors of God's own country, Kerala!

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