By using various web resources, I have gained knowledge about the DNS. The DNS is the essential part of the Internet. DNS stands for Domain Name System. Basically, the main purpose of the DNS is to convert or translate the Internet domain and host names to Internet Protocol Addresses and vice versa. DNS is a “hierarchically distributed database system” that matches host names to the IP addresses. The Domain names are alphabetical, so they are easy to remember and opposite to that, it is hard to remember the numerical IP addresses of the various billions and billions of websites in our brains.
History of DNS
In 1966, the ARPANET (Advanced Research Projects Agency Network) was established to connect the research centers across the United States to share the information faster. Till the late 1980s, total 320 computers were connected with each other within this network. The problem of remembering the numerical IP addresses rose between the people. So, a guy named Paul Mockapetris with the help of Jon Postel and Zaw-Sing Su, published RFC (Request for Comments) 882, which created the Domain Name System to make Internet navigation easier. Thus, it is said that, these guys have invented the DNS.
The primary use of the DNS is to ensure the availability of Websites and E-mails by mapping the domain names to IP addresses, which are represented as a series of numbers and letters. For example, 220.127.116.110(IPv4) or 1001:222:B03:0:0:3:10(IPv6). Specialized servers are used by the DNS to translate names such as www.google.com into IP addresses that allow data and information to reach its destination. This is called DNS resolution, which allows users to type easily memorable domain names in a web browser to reach different websites and send email messages.
The various levels of domains are described below.
1. Top-Level Domain
Top-Level Domain (TLDs) are the highest level of organization on the Web. There are commonly 2 types of TLDs: Generic TLDs such as .com, .net, .org; and Country Code TLDs such as .uk, .ca, .au.2. Second-Level Domain
This appears to the immediate left of the TLD. People, in general, register for the second-level domain to differentiate themselves from other websites.
3. Third-Level Domain
This is also called Sub-Domain, it is the portion of the domain name that appears before the second-level domain name. The most common third-level domain name is www, but can it can be of many other forms like blogs.xyz.com. The texts in bold is called Third-Level Domain.
How DNS works
Below I have described the few steps to provide the information about how the DNS works.
1. First, a User types a domain or web address, let’s say “www.google.com” into a browser. The browser sends a message to the network asking for help, this is called query.
2. The computer queries or contacts one of the machines that the ISP of the user has given to the computer, called Recursive Resolvers. It either should have the IP addresses cached, or is able to go out and recursively find it.
3. If Recursive Resolvers don’t have the address, they query the DNS root name servers for the IP address.
4. The Root name servers direct the ISP’s recursive resolvers to appropriate TLD name servers by matching the Top-Level Domain.
5. Each TLD has its own set of name servers. After the Resolver asks them for the IP address, they refer it to more appropriate set of authoritative DNS servers by reviewing the Second-Level Domain of the query.
6. The ISP’s recursive resolver then queries the referred authoritative DNS name servers for the IP address. Each domain has an assigned set of authoritative DNS name servers that are responsible for knowing everything about the domain, including the IP address(es).
7. The ISP’s Recursive Resolvers of the User retrieves the A record (which is the DNS record for mapping IP addresses) for www.google.com from the authoritative name servers and stores the record in its local cache in case anyone else queries it.
8. Finally, recursive server returns the A record to the User’s computer, which reads and passes the IP address to user’s browser then opens a connection to www.google.com. The entire process happens in a few parts of second and it is transparent to the end user.
The DNS is the necessary thing after having the website URL, to access the Internet. It is like a phone book of the Internet. Today, there are over 300 million registered domains and it is obvious that it is almost impossible for everybody to remember the numerical IP addresses to access various websites. So, the DNS is very essential thing in the world of Internet and Network.