In the world of Internet and the area of computer networks,
you will often come across the term Domain Name System or Domain Name
Service which is simply referred to as DNS. The working of DNS forms
one of the basic concepts of computer networks whose understanding is very much
essential especially if you are planning to get into the field of ethical
hacking or network security.
In this post, I will try to explain how Domain Name System
works in a very simple and easy to follow manner so that even the readers who
do not have any prior knowledge of computer networks should be able to
understand the concept.
What is a Domain Name System?
A “Domain Name System” or “Domain Name
Service” is a computer network protocol whose job is to map
a user friendly domain name such as “arindamcctvaccesscontrol.blogspot.com” to
its corresponding IP address like “173.245.61.120″.
Every computer on the Internet, be it a web server,
home computer or any other network device has a unique IP address allotted to
it. This IP address is used to establish connections between the server and the
client in order to initiate the transfer of data. Whether you are trying to
access a website or sending an email, the DNS plays a very important role here.
For example, when you type “www.google.com” on your
browser’s address bar, your computer will make use of the DNS server to
fetch the IP address of Google’s server that is “74.125.236.37″. After
obtaining the IP address, your computer will then establish a connection with
the server only after which you see the Google’s home page loading on your
browser. The whole process is called DNS Resolution.
With millions of websites on the Internet, it is
impossible for people to remember the IP address of every website in order to
access it. Therefore, the concept of domain name was introduced so that every
website can be identified by its unique name which makes it easy for people to
remember. However, the IP address is still used as the base for internal
communication by network devices. This is where the DNS comes in to action that
works by resolving the user friendly domain name to its corresponding machine
friendly IP address.
In simple words, domain names are for humans while IP
addresses are for network devices. The “Domain Name System” is a protocol to
establish a link between the two. Hence, it is not a surprise that you can even
load a website by directly typing its IP address instead of the domain name in
the browser’s address bar (give it a try)!
Types of DNS Servers and their Role:
The Domain Name System (DNS) is a distributed database
that resides on multiple computers on the Internet in a hierarchical manner.
They include the following types:
Root Name Servers:
The root servers represent the top level of the
DNS hierarchy. These are the DNS servers that contain the complete database of
domain names and their corresponding IP addresses. Currently, there are 13 root
servers distributed globally which are named using the letters A,B,C and so on
up to M.
Local Name Servers:
Local servers represent the most lower level DNS
servers that are owned and maintained by many business organizations and
Internet Service providers (ISPs). These local servers are able to resolve
frequently used domain names into their corresponding IP addresses by caching
the recent information. This cache is updated and refreshed on a regular basis.
How DNS Server Works?
Whenever you type a URL such as “http://www.google.com”
on your browser’s address bar, your computer will send a request to the local
name server to resolve the domain name into its corresponding IP address.
This request is often referred to as a DNS query. The local name server
will receive the query to find out whether it contains the matching name and IP
address in its database. If found, the corresponding IP address (response) is
returned. If not, the query is automatically passed on to another server that
is in the next higher level of DNS hierarchy. This process continues until the
query reaches the server that contains the matching name and IP address. The IP
address (response) then flows back the chain in the reverse order to your
computer.
In rare cases where none of the lower level DNS
servers contain the record for a given domain name, the DNS query eventually
reaches one of the root name server to obtain the response.
FAQs about Domain Name System:
Here is a list of some of the FAQs about DNS:
How does a “root name server” obtain the information about new domains?
Whenever a new domain name is created or an
existing one is updated, it is the responsibility of the domain registrar to
publish the details and register it with the root name server. Only after this,
the information can move down the DNS hierarchy and get updated on the lower
level DNS servers.
What is DNS propagation?
Whenever a new domain name is registered or an
existing one is updated, the information about the domain must get updated on
all the major DNS servers so that the domain can be reached from all parts of
the globe. This is called DNS propagation and the whole process can take
anywhere from 24 to 72 hours to get completed.
How often the DNS servers are updated to refresh the cache?
There is no specific rule that defines the rate
at which DNS servers should be updated. It usually depends on the organization
such as the ISP that maintains the server. Most DNS servers are updated on an
hourly basis while some may update their databases on a daily basis.
I hope you have now understood the working of DNS
in a very convincing manner. Pass your comments and share your opinion.