Up to now we have only been discussing about reaching devices and server by using their network IP address. However, when using the Internet it is quite more frequent to use domain names instead.
Would you visit:
or would you rather visit:
The Domain Name System allows the translation of a domain name into the corresponding IP address. For the purpose of this tutorial, you can think of it as a big table with two columns and several rows. Each row contains a domain name in the first column and an IP address in the second column. Domain Name Servers can, on request, read this table and translate a domain name with the corresponding IP, that is then used for processing network requests. Domain names are a semantical layer that sit on top of the IP addresses system. DNS links the names layer with the IP layer.
DNS is used every time you (and the other billions of Internet users) visit a website by using a domain name. Every time the same people send an e-mail at an address like firstname.lastname@example.org (as opposed to email@example.com). So it is one of the foundations of the Internet as we use it every day.
“The Domain Name System (DNS) is a hierarchical distributed naming system for computers, services, or any resource connected to the Internet or a private network. It associates various information with domain names assigned to each of the participating entities. A Domain Name Service resolves queries for these names into IP addresses for the purpose of locating computer services and devices worldwide. By providing a worldwide, distributed keyword-based redirection service, the Domain Name System is an essential component of the functionality of the Internet.”
You may have noticed, on configuring internet access for a device that DNS is indeed one of the parameters you should somehow deal with. Sometimes DNS can be obtained automatically from your ISP, other times you have to enter it manually. See for example the basic configuration settings for a router in Figure 1-11 on this page. DNS is so important that you generally need to enter a primary DNS, and a secondary DNS (that will be used if the primary DNS fails).
Internet addresses or Uniform Resource Locators (URLs) will be discussed in detail in a subsequent chapter of this tutorial.
You can continue reading about the Linux operating system in Chapter 2