What is DNS ? How does it work ?

Question: What is DNS ? How does it work ?

Answer 

DNS, or the Domain Name System, translates human readable domain names (for example, www.amazon.com) to machine readable IP addresses (for example, 192.0.2.44).

There are 4 DNS servers involved in loading a webpage: 

DNS recursor/ DNS resolver: It is basically provided by the ISP (like Jio, Airtel, Idea). The DNS recursor is a server designed to receive queries from client machines through applications such as web browsers. Typically the recursor is then responsible for making additional requests in order to satisfy the client’s DNS query.

Root Name Server: It is operated by 12 organizations. There are 13 sets of root name servers. A name server is a computer that answers questions about domain names, such as IP addresses. These 13 servers act as a kind of telephone switchboard for DNS. They don’t know the answer, but they can direct DNS queries to someone that knows where to find it.

TLD Name Server: The top level domain server (TLD) is the next step in the search for a specific IP address, and it hosts the last portion of a host name (In example.com, the TLD server is “com”). Each TLD, such as those for .com, .org, and .us, has its own set of name servers, which act like a receptionist for each TLD. These servers don’t have the information we need, but they can refer us directly to the servers that do have the information.

Authoritative Name Servers: The authoritative name server is the last stop in the name server query. These authoritative name servers are responsible for knowing all the information about a specific domain, which is stored in DNS records. The authoritative name server has access to the requested record and it will return the IP address for the requested host name back to the DNS Recursor that made the initial request.

A user opens a web browser, enters www.example.com in the address bar, and presses Enter.

The request for www.example.com is routed to a DNS resolver, which is typically managed by the user's Internet service provider (ISP), such as a cable Internet provider, a DSL broadband provider, or a corporate network.

The DNS resolver for the ISP forwards the request for www.example.com to a DNS root name server.
The DNS resolver for the ISP forwards the request for www.example.com again, this time to one of the TLD name servers for .com domains. The name server for .com domains responds to the request with the names of the four Amazon Route 53 name servers that are associated with the example.com domain.
The DNS resolver for the ISP chooses an Amazon Route 53 name server and forwards the request for www.example.com to that name server.
The Amazon Route 53 name server looks in the example.com hosted zone for the www.example.com record, gets the associated value, such as the IP address for a web server, 192.0.2.44, and returns the IP address to the DNS resolver.

The DNS resolver for the ISP finally has the IP address that the user needs. The resolver returns that value to the web browser. The DNS resolver also caches (stores) the IP address for example.com for an amount of time that you specify so that it can respond more quickly the next time someone browses to example.com. For more information, see time to live (TTL).

The web browser sends a request for www.example.com to the IP address that it got from the DNS resolver. This is where your content is, for example, a web server running on an Amazon EC2 instance or an Amazon S3 bucket that's configured as a website endpoint.
The web server or other resource at 192.0.2.44 returns the web page for www.example.com to the web browser, and the web browser displays the page.