Domain Name System (DNS)
The Domain Name System (DNS) was conceived in 1984, basically a lookup translation table converting machine readable IP addresses into human understandable names. Locating a website by its name www.example.com rather than entering 188.8.131.52 in the browser address bar makes eminently more sense. These translation tables – name servers – are dotted across the Internet and contain specific references to website/IP addresses on their own local list, pointers to other name servers who may be able to locate the desired computer should it not be found locally and a cache (temporary list) of recently requested domain names.
Name servers are maintained and updated on a daily basis as IP addresses change or are added when new websites come online. Millions of people and automated systems maintain this distributed naming system worldwide and it is accessed by billions of surfers each day, requesting not just websites but email addresses and FTP servers. It is the biggest and most active distributed database in the world. There are special name servers called root servers which hold the addresses of all the Top-Level Domains (TLDs like .com, .co.uk, .net. .org, etc.). These are frequently interrogated whenever an unknown domain name (website) is requested and point the requesting name server to the address of the server holding the translation table or map for the requested website.
Obviously a single name server holding all internet addresses would be immediately brought to its knees so there are several servers duplicating domain addresses at various levels of the system and hundreds of thousands worldwide which, as well as speeding up the process of web access, serve as a layer of inbuilt redundancy should local failure occur.
All name servers are not updated immediately – which is why a new website is not instantly visible across the Internet. Additions to name server lists take time to propagate around the world but are usually achieved within a day or two.
Various organizations are responsible for individual TLDs, ensuring duplicate domain names cannot exist. These often country-specific organisations employ registrars, businesses accredited to register and lease domain names to companies and individuals.
Nowadays the registration process is automated and remarkably simple. Choose a domain name, check it is not already registered, select the lease period (no, you don’t actually own the domain but the right to use it for a period of time, a minimum of one or two years) … and pay for it.
The domain is then added to the registrar’s local domain name server and propagated to the world’s root name servers. Whether a website exists for the domain is immaterial, its potential existence and location is described and forwarded. Web hosting companies may or may not be registrars which means a domain may be registered with one company but hosted – made visible to the Internet through a web server – by another. In this instance, the domain will be registered and a change must be made to the default name servers list to point to another set of name servers owned by the hosting company.
Actually developing a website is another matter. With the creation of HTML (HyperText Markup Language), Tim Berners-Lee offered developers the opportunity to apply special tags to describe the structure and shape of documents – web pages. The initial minimal set has been supplemented to include about 90 tags serving different purposes such as presenting headings, titles and lists to embedded multimedia and graphical objects – though not without some disdain since Berners-Lee at one time was at odds with Netscape for introducing the image tag which he felt was making the Web frivolous.
Once a website or indeed any internet destined documents have been constructed they are invariably transferred to the host server by means of FTP (File Transfer Protocol) by opening a channel to the web server using either a browser connection string, for instance, ftp.yourdomain.com entered into a browser address bar or via a dedicated FTP client, a software program designed specifically for the bi-directional transfer of files. Some are standalone, some are an inbuilt feature of website design programs.
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Article: Domain Name Sysetm (DNS) (Part.5) written by Vincent Zegna and Mike Pepper. Published 23rd November 2005.