What is a Domain Name System DNS ?
-In the world, networking computers don’t go by names
like we do, they go by numbers because this is how computers and other similar devices
communicate and identify with each other over a network which is by using
numbers such as IP addresses,
in order to bridge the communication gap between
computers and humans and make the communication a lot easier networking
engineers developed DNS,
DNS stands for a domain name system, and DNS resolve
names to numbers to be more specific it translates domain names to IP addresses
For each IP address, there is a name of a network
interface (computer)—or to be exact, a domain name. This domain name can be
used in all commands where it is possible to use an IP address. A single IP
addresses can have several domain names affiliated with it. The relationship
between the name of a computer and an IP address is defined in the Domain Name
System (DNS) database. The DNS database is distributed worldwide.
DNS Brief History :
- Thirty years ago when you were willing to visit a website you had to know the IP address of that site, because computers were and
still only able to communicate using numbers:
Here is an example of an IP address 102.54.94.97.
it is long and hard to remember, therefore we needed a
way to translate computer-readable information into human-readable information
in 1983 Paul Mockapetris designed the Domain Name System and wrote first
implementation, then mapped IP address to domain names, and voila
A DNS was born, this system still serves as the mainstay of the modern internet;
today
DNS structure
-The DNS process domain names following their
hierarchical structure a dm=omain name is composed of different parts separated by “dots” and each part
represents a hierarchy in the domain name structure and this hierarchy descent
from the right to the left part of the domain name.
-The drawing above shows a partial DNS hierarchy. At the top is what is called the
root and it is the start of all other branches in the DNS tree.
- DNS is hierarchical in
structure. A domain is a subtree of the domain namespace. From the root, the
assigned top-level domains in the U.S. are:
GOV – Government body.
EDU
– Educational body.
INT
– International organization
NET
– Networks
COM
– Commercial entity.
MIL
– U. S. Military.
ORG
– Any other organization not previously listed.
How a DNS works
-The DNS directory that matches the names to
numbers aren’t located all in one place in some dark corner of the internet.
Like the internet itself, the directory is distributed around the world, stored
on domain name servers that all communicate with each other on a very regular
basis to provide updates and redundancies. with more than 337 million domain
names and still going,
Every time a DNS query is made, the
root servers are the first servers to be contacted. However, there is no need
to contact the root servers every time a query is made since results can be
obtained from the DNS cache which stores information for recent previous
queries. If the DNS server does not find the results in the cached copies it asks
a series of servers through a process called recursion until it reaches the
authoritative name servers for that domain.
Each named site can correspond to more
than one IP address. In fact, some sites have hundreds or more IP addresses
that corresponds with a single domain name. For example, the server your
computer reaches for www.google.com is likely completely different from the server
that someone in another country would reach by typing the same site name into
their browser
DNS information is shared among many
servers, but is also cached locally on client computers. Chances are that you
use google.com several times a day. Instead of your computer querying the DNS
name server for the IP address of google.com every time, that information is
saved on your computer so it doesn’t have to access a DNS server to resolve the
name with its IP address.
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