Have you ever wondered what happens when you type a URL into your browser and press Enter? The process is quite complex and involves several steps, including DNS resolution, establishing a TCP/IP connection, navigating through firewalls and load balancers, and serving content from various servers and databases.

Let's walk through the steps involved so as to understand what happens when you type google.com in your browser.

DNS Request

When you enter a URL into your browser, the first thing that happens is a DNS (Domain Name System) lookup. DNS is a hierarchical system that maps domain names to IP addresses. The DNS lookup is necessary to find the IP address of the web server that hosts the website you're trying to access.

Here's an example of a DNS request for google.com:

$ nslookup www.google.com
Server:         192.168.0.1
Address:        192.168.0.1#53

Non-authoritative answer:
Name:   www.google.com
Address: 216.58.223.228
Name:   www.google.com
Address: 2c0f:fb50:4003:802::2004

This command sends a DNS request to your local DNS server, which then sends a request to the DNS server responsible for the top-level domain (.com). The top-level domain server responds with the IP address of the DNS server responsible for the google.com domain. Your local DNS server then sends a request to the google.com DNS server, which responds with the IP address of the web server hosting google.com.

TCP/IP

Once your browser has obtained the IP address of the web server, it establishes a TCP/IP (Transmission Control Protocol/Internet Protocol) connection with the server. TCP is responsible for establishing a reliable, ordered, and error-checked connection between two applications, while IP is responsible for routing packets of data between hosts on the internet.

Here's an example of a TCP/IP connection using the telnet command:

$ telnet www.google.com 80
Trying 216.58.223.228...
Connected to www.google.com.

This command establishes a TCP connection with the web server hosting google.com on port 80 (the default HTTP port). Once the connection is established, your browser sends an HTTP request to the server, asking it to send back the web page you requested.

Firewall

Before the TCP/IP connection can be established, it must first navigate through any firewalls or proxy servers that may be in place. Firewalls are network security systems that monitor and control incoming and outgoing network traffic based on predetermined security rules. They can prevent unauthorized access to your network and protect your systems and data from security threats.

HTTPS/SSL

If the website you're accessing uses HTTPS (HTTP Secure), the TCP/IP connection will be encrypted using SSL (Secure Sockets Layer) or TLS (Transport Layer Security) to ensure the privacy and security of the data being transmitted. SSL/TLS use public key cryptography to establish a secure connection between the client and the server. This prevents third parties from intercepting or tampering with the data being transmitted over the internet.

Load-balancer

In some cases, the web server hosting the website may be overloaded with traffic, or there may be multiple web servers handling requests for the same website. In these cases, a load balancer is used to distribute the incoming traffic evenly across multiple servers to ensure that no single server is overwhelmed. Load balancers can be hardware or software-based, and they use various algorithms to determine how to distribute the traffic.

Web server

Once the TCP/IP connection is established and any necessary security measures have been put in place, the web server hosting the website sends back the requested web page to your browser. Web servers are software applications that run on web servers and are responsible for serving content to clients over the Internet.

Application server

In some cases, web pages may be dynamically generated based on user input or other factors. In these cases, an application

Web server

Finally, the request reaches the web server. The web server receives the request and begins to process it. The web server is responsible for sending back a response to the client. In this case, the web server will generate an HTML page with the search results.

Application server

The web server then sends the request to the application server. The application server is responsible for executing the server-side code and generating the dynamic content that the user sees. In this case, the application server will execute the search query and return the results to the web server.

Database

The application server then sends a request to the database to retrieve the search results. The database will execute the query and return the results to the application server.

Response

Finally, the application server sends the search results back to the web server. The web server then sends the response back to the client, which is the user's browser. The response contains the search results in the form of an HTML page, which the browser will render and display to the user.

Conclusion

When you type google.com into your browser and press Enter, a complex series of processes begins. The browser sends a DNS request to translate the domain name into an IP address. The browser then establishes a TCP/IP connection to the server, passes through any firewalls, and negotiates an SSL/TLS connection if necessary. The server then passes the request to a load balancer, which distributes the request to a web server. The web server sends the request to an application server, which executes server-side code and retrieves data from the database. The application server then sends the search results back to the web server, which sends the response back to the browser. All of this happens in a matter of seconds, allowing you to quickly and easily search the web.