DNS:The Internet Mapper

The internet generation folks must have across the term DNS at some point of their lives. We have seen messages like DNS error or cannot find server. This post unravels the working of DNS.

What is DNS?

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 “facebook.com” to its corresponding IP address like “173.252.110.27″.

Need and Working

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.

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:

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.

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