What happens when you type google.com in your browser and press Enter

1. DNS Request

The Domain Name System (DNS) is the first step in accessing any website. Here’s what happens:

• Browser Initiation: You type “https://www.google.com" in your browser and press Enter.
• DNS Resolution: Browser Cache Lookup: First, your browser checks its cache to see if it recently resolved “www.google.com" to an IP address. If found, it skips further DNS resolution steps and proceeds directly.
• Operating System DNS Resolver: If the domain name is not found in the browser cache, the browser queries the operating system’s DNS resolver.
• ISP DNS Resolver : If the operating system’s resolver doesn’t have the IP address for “www.google.com” cached, it sends a recursive DNS query to the DNS resolver provided by your ISP. The ISP’s DNS resolver checks its cache to see if it has a recent record of the IP address for “www.google.com". If not found in its cache, the ISP’s DNS resolver continues the recursive query process.
• authoritative DNS servers: It queries root DNS servers to find the authoritative DNS servers for the top-level domain (TLD), in this case, “.com”. Then, it queries the authoritative DNS servers for “google.com” to obtain the IP address of “www.google.com".
• IP Address Retrieval: Once the IP address for “www.google.com" is resolved, it is cached for future use.

2. Establish TCP/IP

When you click a link to a website, your computer and the web server need to establish a TCP connection to talk to each other. This happens in three steps:

• Three-Way Handshake: 1- The browser initiates a TCP connection with the server by sending a SYN packet. 2- The server responds with a SYN-ACK packet. 3- browser acknowledges this with an ACK packet.

This establishes a reliable connection between the browser and the server.

3. Firewall

the firewall checks to ensure that the particular request you are making is allowed before permitting it. Also, if the server you are trying to access is also behind a firewall, a similar check will be done before you are finally able to connect to the server. Firewall inspection has different methods, but it generally involves examining data packets that enter or leave your network. Here’s how it works:

• packet filtring: is a fundamental technique used in network security to control the flow of data packets entering or leaving a network. It operates at the network layer (Layer 3) of the OSI model and examines packets based on predetermined criteria, such as source/destination IP addresses, source/destination port numbers, protocol types (e.g., TCP, UDP), and other header information.
• statefull inspection: also known as dynamic packet filtering, enhances network security by examining not only individual packets but also the context of the entire communication session. This approach operates at the network and transport layers (Layers 3 and 4) of the OSI model.
• Deep Packet Inspection (DPI): ) is an advanced method of packet filtering that goes beyond traditional header-based analysis. DPI examines the actual data (payload) within packets at layers higher than the network layer (Layer 7 of the OSI model), such as the application layer.

4.Load Balancer Handling:

Many large websites like Google use load balancers to distribute incoming traffic across multiple servers for improved performance, scalability, and availability. Traffic Distribution: Before forwarding your request to a specific server, the load balancer performs: Load-Balancing Algorithm: Determines which server (e.g., based on current load, geographic proximity) will handle your request. Forwarding: Once a server is selected, the load balancer forwards your TCP connection request to that server.

5. https/ssl connection:

After establishing the connection, your browser now sends a request for the webpage using an encryption protocol like Secure Sockets Layer (SSL) or Transport Layer Security (TLS) in order to encrypt the data that will be shared between your computer and the server. This type of encryption is what is responsible for the “s” in “https” which also implies that the connection is secure. SSL/TLS Handshake:

Client Hello: Your browser sends a Client Hello message to the server, specifying supported SSL/TLS versions and encryption algorithms. Server Hello: The server responds with a Server Hello message, choosing a compatible SSL/TLS version and encryption algorithm from the client’s list. Certificate Exchange: The server sends its digital certificate, which includes its public key used for encryption. Key Exchange: Your browser generates a symmetric session key and encrypts it with the server’s public key from the certificate. Session Established: Once both parties agree on the session key, they can securely exchange encrypted data for the remainder of the session.

6. Web Server Processing:

With the HTTPS session established, the selected web server processes your HTTPS request: Request Handling: Parses the HTTPS request (e.g., GET / HTTP/1.1) to determine the requested resource. Dynamic Content Generation: Executes backend application logic if necessary (e.g., fetching search results from a database).

7. Database:

For dynamic content, the web server may interact with databases: Query Execution: Retrieves necessary data (e.g., search results, user information) from databases. Data Formatting: Prepares the retrieved data for inclusion in the HTTP response.

8. HTTP Response Generation:

The web server constructs an HTTPS response: Status Line: Indicates the HTTP version and status code (e.g., 200 OK). Headers: Includes metadata about the response (e.g., Content-Type, Content-Length). Response Body: Contains the actual content of the webpage (HTML, CSS, JavaScript, images).

9. Transmission and Rendering:

The server sends the HTTPS response back through the established TCP connection. Browser Rendering: Your browser receives the response, processes HTML, CSS, and JavaScript, and renders the webpage on your screen.

Conclusion

when you initiate a request by typing “https://www.google.com" in your browser, the process involves DNS resolution to find the server’s IP address, TCP/IP connection establishment for reliable communication, load balancer involvement for distributing traffic, HTTPS protocol negotiation for secure data exchange, web server processing for handling requests, application server interaction for executing business logic and possibly database interaction for data retrieval. Each component collaborates to ensure efficient, secure, and responsive delivery of web content, especially critical for services like Google’s search engine that handle massive amounts of user traffic and dynamic content.