Interesting bits of information

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14 December 2013

Adrian Fowler

Adrian Fowler
Founder

A brief explanation into DNS. How a DNS Server works and what it does.
Adrian

What is a DNS Server

Each electronically connected resource, whether it be a personal computer, printer, mail server, web server or website etc. if connected to another device, for example your personal computer is connected to the internet, or your printer is connected to your local area network, has an IP address.

IP addresses are just numbers described as a numerical label assigned to each device. In the case of IPv4, for example 172.0.0.1, these can mean little to humans and be difficult to remember.

DNS Server is like an address book

DNS takes care of that by assigning a meaningful name to an IP address. Take for example http://www.web-lab.co it resolves to an IP address of 109.68.195.84. This is because something called a DNS entry was created, in the form of an A (Host) record. When someone types into the web browsers’ address bar  www.web-lab.co it automatically translates this into the numbers 109.68.195.84 because the record created for ‘www’ was told to do so and stored in a DNS record on a DNS server. This makes it a lot easier for humans to remember as it makes sense as we can remember things like web-lab.co, google.com, amazon.co.uk etc.

In the world, there are 13 Root Servers which act as global DNS Servers. Each record created by each and every one of us is stored on these DNS Servers. These Servers store public records only, so in other words, whatever web page is published publically, the domain for the web page, i.e. the bit after the www part and the bit before the .co.uk part will be pointing to an IP address. The same goes for email, if someone send you an email to (assuming this was your address) someone@somcompany.co.uk, the ‘somecompany.co.uk’ part is translated into an IP address (Called an MX Record in this case) and the email then is able to find its way to the correct email servers. Oncve the request is received to a domain, the DNS server decides if it’s an email, or a web page request and sends the traffic accordingly. All thanks to DNS servers.

For a Local Area Network (LAN) it is similar, but the DNS Servers aren’t made public, i.e. not accessible to the Internet. You may have a printer on your network, or a server sharing files and folders, these again have unique IP addresses which are named in a similar way. For example you may have a file server called SRV-1 which resolves to an IP address 192.168.0.10. So when you do a search for srv-10, you are in fact essentially asking for a search of 192.168.0.10 because the DNS Server configured on your LAN resolves the name to the IP address.

Interesting fact

Some of these DNS Server are located in places such as NASA, US Department of Defence, US Army, ICANN, University of Southern California, RIPE NCC etc., and each one of these 13 named authorities manage 100’s of individual DNS Servers around the world.

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