Domain Name Service - DNS Explained

DNS Explained ...

Many people have heard the term DNS (Domain Name Service) without understanding what it means or what it does. Learn why DNS is essential to the smooth operation of the Internet. Without it, users would have to learn to use IP Numbers instead of Domain names. DNS uses a system of name resolution is the Internet equivalent of a telephone directory and this Internet DNS tutorial demonstrates how it operates. This howto is intended to unravel in simple terms, what DNS is and how it works but you should note that it does not cover dynamic DNS which is a different subject.

Two Different Methods ...

Let us presume that you are sitting at your computer and that you are connected to the Internet. You decide that you would like to visit W3C, the World Wide Web Consortium Website which may be thousands of miles away, across oceans and continents. There are two different methods that you can use to achieve this, one primarily designed for human beings and the other primarily designed for computers and the Internet.

The first method is to use a domain name (e.g. 'www.w3.org') and I am sure that most Internet users can think of several examples of domain names. The second method is to use an IP Address (e.g. '128.30.52.24') and I would bet that very few of you could think of or remember examples of IP Addresses. Yet from your point of view they will both achieve an identical end result, that is to connect you to the World Wide Web Consortium Website. We have provided the adjoining graphic to illustrate this and if you would like to try both options for yourself then please do so.

The Internet's Method ...

I don't think that any of us would win too many prizes for correctly guessing which of these two methods the Internet is capable of using. On the basis that computers can understand numbers but they can't understand human names and phrases, then the Internet's method of connecting you to www.w3.org has to be the IP Address which is a number.

The actual process is as follows. You type an IP Address into your browsers Address bar and the browser transmits this IP Address to the computer belonging to your ISP (Internet Service Provider) that controls your connection to the Internet. The ISP's computer then routes you through the Internet to connect you to your destination (e.g. 'www.w3.org'). Apart from controlling your access to the Internet this routing is the only job that the ISP's computer does, and it cannot understand domain names.

The Human Method ...

Human beings would soon realise their limitations if the had to use IP Addresses all the time to make their Internet connections, so a system was developed called DNS (Domain Name Service) which enables humans to make their Internet connections using human type names and descriptions (i.e. domain names).

The best analogy I can use to describe DNS is to compare it to telephone directories, the difference being that telephone directories are based on a geographical area (e.g. city, town, etc.) whereas DNS is based on the top-level portion of the domain name (e.g. ".com", ".co.uk", etc.). You should remember that there are literally hundreds of top-level domains, many that you are probably not even aware of (e.g. ".to" for Tonga, ".au" for Australia, etc.) in the same way there are hundreds of telephone areas in a country. The other difference is that DNS returns an IP Address (number) from a domain name, whereas telephone directories return a telephone number from a persons name.

DNS Server Types ...

At this stage I am going to to jump ahead a little to tell you that the Domain Name Service has special Host servers dotted around the Internet and that there are three different types of these (DNS) nameservers.

• ROOT NAME SERVERS
  These are the top level servers in the DNS system and their are only thirteen of these rootservers throughout the world. A root server is there to control a database that contains the location of DNS primary name servers for every top-level domain in the world (e.g. "com", "co.uk", etc). Local name servers send them the top-level portion of a domain name (e.g. "com", "co.uk", etc) and they look-up and return the IP Address of the primary name server that contains the DNS database for that particular top-level domain.

• PRIMARY NAME SERVERS
  A primary name server controls the DNS database for a given top-level domain (e.g. "com", "co.uk", etc.). Local name servers send it the second-level portion of a domain name (e.g. 'web-wise-wizard') and it looks-up and returns the corresponding IP Address (e.g. '216.147.58.27') to the requesting local name server.

• LOCAL NAME SERVERS
  Local name servers are your point of contact with the DNS system (more of that later). Your browser sends the local name server a domain name (e.g. 'web-wise-wizard.com'). They split the domain name and start by sending the top-level portion of the domain name (e.g. "com") to a DNS root name server. The root name server looks-up and returns the address of the DNS primary name server that contains the corresponding database for that top-level domain. The local name server then sends the second-level portion of the domain name (e.g. 'web-wise-wizard') to the specified primary name server which looks-up and returns the IP Address for the domain. The local name server then returns the IP Address to your browser.

The thirteen root name servers are all operated by Network Solutions Inc. and Network Solutions estimate that 70% of all Internet traffic is used by the DNS system. This does not bode well for DNS in the longer term but in the meantime it's the only system we have and it does work fairly well.

Local Name Servers ...

There is still one link in the chain that we have not discussed yet. When you first type your URL into the browsers Address bar how does the browser know how to find a DNS local name server to start the process of converting your target domain name into an IP Address?

If you remember our earlier discussion the browser only has one link to the outside world, which is to your ISP's computer that handles your connection to the Internet and this computer only understands and accepts IP Addresses.

The answer is straightforward and if you have ever manually configured a TCP/IP connection to the Internet, you may realise that you know the answer to this question.

Part of the TCP/IP connection setup (usually in Dial-Up-Networking) for any connection to the Internet includes two IP Addresses. In Windows NT these are called Primary DNS and Secondary DNS and the adjoining graphic demonstrates their usage. Strictly speaking only one of these IP Addresses is necessary but the rules of the Internet dictate that DNS servers must always operate in pairs, in case one breaks down or becomes unavailable.

These two IP Addresses both point to DNS local name servers (not DNS root name servers or DNS primary name servers) and so that you can start to put DNS local name servers into context I am going to tell you a secret.

DNS local name servers are the same the world over and technically you don't have to use the servers specified in your ISP's TCP/IP setup.

A Small Experiment ...

Which brings us to a totally unrelated point. If you are having problems with your Internet connection, especially at peak times, there is a more than even chance that the problem lies with your DNS local name server being overloaded and not your target 'http' server which usually gets the blame. Remember that 70% of Internet traffic is DNS traffic.

Try swapping the two IP Addresses around. If for example, your ISP has 10,000 Internet connections and they are all using the same primary DNS local name server at the same time then swapping the IP Addresses around could mean that you get exclusive usage of the secondary DNS local name server. Internet connection problems solved!

Before trying this make sure that you carefully take a note of both IP Addresses so that if you later make a mistake and get into trouble you can revert to the original configuration.

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