DNS, Domain Name Server

Well, In this article, you wondered where DNS came from,.. It also help you understand why DNS servers are run mostly on LINUX and and UNIX- type system. We then get to see the layers of the OSI Models on which DNS works and, towards the end of the page, you will find out how the Domains (and DNS servers) are structured on the Internet to ensure uptime and effectiveness.

The history, DNS has began in early days when the internet was only the small network created by Department of Defense for research purposes. Host names (simple computer names) of computers were manually entered into a file (called HOSTS) which was located on a central server. Each site/computer that needed to resolve host names had to download this file. But as the number of hosts grew, so did the HOSTS file (Linux, Unix, Windows and NetWare still use such files) until it was far too large for computers to download and it was generating great amounts of traffic.

The Domain Name System is a 'hierarchically distributed database', which is a fancy way of saying that its layers are arranged in a definite order and that its data is distributed across a wide range of machines (just like the roots of a tree branch out from the main root).

Most companies today have their own little DNS server to ensure the computers can find each other without problems. If you're using Windows 2000 and Active Directory, then you surely are using DNS for the name resolutions of your computers. Microsoft has created its own version of a "DNS" server, called a WINS server, which stands for Windows Internet Name Service, but this is old technology and uses protocols that are nowhere near as efficient as DNS, so it was natural for Microsoft to move away from WINS and towards DNS, after all, the whole Internet works on DNS


The DNS protocol normally uses the UDP protocol as a means of transport because of its small overhead in comparison to TCP; the less overhead a protocol has, the faster it is !

In the case where there are constant errors and the computer trying to request a DNS resolution can't get an error free answer, or any answer at all, it will switch to TCP to ensure the data arrives without errors.

The Internet Domain Name Server Hierarchy

This interesting section will help you understand how domain names on the Internet are structured and where DNS servers fit in to the picture. When you think about the millions of domain names registered today, you probably think that you have to be superhuman to manage such a structure of DNS Server.

Well that's not that case. The DNS structure has been designed in such a way that no DNS Server needs to know about all possible domains, but only those immediately above and below it.

The picture below shows part of the Internet DNS hierarchical structure:

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Let's explain how it works :

Internic controls the "root" domain, which includes all the top level domains. These are marked in a green oval for clarity. Within the green oval you have the ROOT DNS servers, which know all about the authoritative DNS servers for the domains immediately below them e.g firewall.cx, cisco.com, microsoft.com etc. These ROOT DNS servers can tell you which DNS server takes care of firewall.cx, cisco.com, microsoft.com and the rest.

Each domain, including the ones we are talking about (cisco, firewall, microsoft), have what we call a "Primary DNS" and "Secondary DNS". The Primary DNS is the one that holds all the information about its domain. The Secondary acts as a backup in case the Primary DNS fails. The process in which a Primary DNS server sends its copy to the Secondary DNS server is called Zone Transfer and is covered in the DNS Database section.

Today there are hundreds of websites at which you are able to register your own domain and, once you've done that, you have the power to manage it yourself. In the example above, Cisco bought the "Cisco.com" domain and then created your resource records. Some examples of resource records for the Cisco domain in our example are: support , www and routers. These will be analysed in depth on the next pages.

So here comes the million dollar question :)

Well lets say, it simple to understand a dns was originally converted in ip protocol so it easy to navigate a name rather than an ip protocol

Address resolution mechanism

Domain name resolvers determine the appropriate domain name servers responsible for the domain name in question by a sequence of queries starting with the right-most (top-level) domain label.

A DNS recursor consults three nameservers to resolve the address www.wikipedia.org.

The process entails:

1. A network host is configured with an initial cache (so called hints) of the known addresses of the root nameservers. Such a hint file is updated periodically by an administrator from a reliable source.
2. A query to one of the root servers to find the server authoritative for the top-level domain.
3. A query to the obtained TLD server for the address of a DNS server authoritative for the second-level domain.
4. Repetition of the previous step to process each domain name label in sequence, until the final step which returns the IP address of the host sought.