Behind the scenes of modern browsers

The equivalent of typing a URL is typing an IP address. However, since it is impossible for a user to remember an infinite number of IP addresses, DNS records were created. The Domain Name System is a database that stores names associated with a given IP address that identifies a host web server on the web. A DNS record is, in fact, a friendly name that allows us to access a difficult to remember IP by typing a site’s name in the URL.

But where does the DNS lookup take place? To answer that question, the first lookup is performed on 4 different cache memories.

Now, what if the site we are looking is not in those caches? In that case ISP’s DNS server will execute a query to find our target IP. This query will be a recursive call to search multiple DNS servers around the world and it will move from one server to another until we either find the IP we want or an error response is returned.

Nowadays most sites contain a third-level, second level and top level domain. Each of these level contains their own name server, which is queried during the DNS lookup process.

For example, for aws.amazon.com, the DNS resolver will contact the root name server first. This will redirect the query to the .com domain name server, which will find the matching IP for amazon.com, which will search for the server corresponding to aws.amazon.com

This is possible thanks to the transmission of packets that contain information about the content and destination of the request. These packets travel over the Internet throughout multiple networking equipment between the client and the server before the correct DNS server is reached. Here is where routing tables come into play, thus helping to figure out the fastest possible way for a packet to reach its intended destination.

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