IP Addresses and Domains

In computer networks, every single machine is identified by a numerical label called an IP address like 203.0.113.1 (IPv4) or 2001:0db8:0f61:a1ff:0000:0000:0000:0080 (IPv6). As IP addresses are hard to remember, the Domain Name System has been invented. DNS allows IP addresses to be mapped to names, exactly in the same way as a telephone directory maps phone numbers to people’s name. Before contacting a machine, its name must be resolved, which means translated to the corresponding IP address. This is done by sending a name resolution request to a DNS server which will answer with the IP address.

Names used in DNS, called domain names, have a particular structure. They are basically divided in two parts : the first, or top, level domain also called extension or TLD, and the second level domain. For example, in rudeotter.com the first level domain is ‘.com’ and the second level domain is ‘rudeotter’.

 

Domain Name Registration

On the internet, the attribution of names is done by specialized hierarchical organisms. At the top of the hierarchy is ICANN who is responsible for all the TLDs (.com, .org, .us, .fr, …). Then comes the different registries, each registry is responsible for one top level domain. ICANN and registries’ roles are purely technical. At the third level of the hierarchy are the registrars, they are the commercial companies which take the different registration requests from people and reserve the domain name at the main registry. The pricing mainly depends on the TLD used, the length of ownership and the country of registration.

During the registration process, contact information with a few pieces of technical information must be provided. Such information are stored in a database called WHOIS database. However, at this level, the newly registered name still doesn’t map to an IP address. To do so, most of the registrars, like 1&1 or OVH, provide a user interface to update the corresponding entry in their own DNS servers. Then, the modifications will be echoed on all the DNS servers over the world.

Once the domain name has been acquired, the owner is solely responsible for it. With the domain name, one can create subdomains, which are parts of the domain identified by different names. Again, like domain names, the subdomain names are divided in levels, separated by dots. For example, blog.rudeotter.com is a subdomain of rudeotter.com. The DNS servers must be configured to handle these different subdomains.

After expiration of the domain name, the corresponding entries in the WHOIS database and in all the DNS servers over the world are deleted. To avoid that, it is important to start the renewal process soon enough.

For further reading after this brief introduction to DNS, try the tags DNS or domain registration.

This is a guest post by Marcus Lyons.

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