Understanding The Anatomy of a URL: What Happens When You Type "google.com" in Your Browser and Press Enter

In the vast world of the internet, every action you take—clicking, tapping, or typing—triggers a complex sequence of events. It's like navigating a network of roads. Each URL you type into your browser serves as a digital address, leading to a destination housed within servers scattered across the globe. But what really happens when you type "google.com" and press Enter?

0. URL Aliasing

Every URL across the internet is made up of:

• Protocol
• Subdomain
• Domain Name
• Path/Page

However, we only typed "google.com", so how does the browser magically come up with the full URL "https://www.google.com"?

Before initiating the DNS request, the browser may perform URL aliasing. In this step, if the entered URL lacks a protocol (e.g., "https://" or "https://"), the browser assumes the default protocol, typically "https://". Additionally, if the URL lacks a subdomain (e.g., "www"), the browser may prepend "www" to the domain name. After aliasing, the browser proceeds with the DNS resolution process described in the subsequent step.

1. DNS Request

Every website is hosted on a separate IP address-based machine. Since IP addresses are difficult to remember, we must convert them into a language that is understandable to humans ("google.com" is simpler to remember than "142.251.37.238"). In order for the browser to find the website, the DNS server's next task is to translate it back to its original IP address. Upon entering https://www.google.com into your browser and hitting Enter, a DNS (Domain Name System) request is made.

How DNS Server Works?

1. The user types www.google.com into the address box and hits Enter.
2. The computer sends a DNS request to the DNS resolver, which is usually provided by your Internet Service Provider (ISP) or a public DNS resolver like Google DNS.
3. If the DNS server does not have the IP address for "www.google.com" cached locally, it starts the resolution process by querying the root DNS servers. These servers maintain information about the authoritative DNS servers for top-level domains like ".com", ".org", etc.
4. The root DNS servers direct the DNS query to the appropriate TLD (Top-Level Domain) DNS server, in this case, the ".com" TLD server.
5. The ".com" TLD server responds with the IP addresses of the authoritative DNS servers responsible for the "google.com" domain.
6. The user's DNS server then sends a query to one of Google's authoritative DNS servers, asking for the IP address of "www.google.com".
7. Google's authoritative DNS server responds with the IP address associated with "www.google.com", such as 142.251.37.238.
8. The user's DNS server caches the IP address for future use to improve performance and reduce the need for repeated queries.
9. Finally, the user's device receives the IP address for "www.google.com" from their DNS server. The web browser can now send an HTTP request directly to that IP address to fetch the webpage from Google's servers.

How to know the IP of a given domain?

In order to know the IP of any domain, you can use the 'nslookup' command to get information from the DNS server.

$ nslookup google.com        

?? This means that if you type 142.251.37.238 into the browser, it will have the same effect as typing google.com.

2. TCP/IP

After the DNS request is completed, your browser establishes a TCP/IP connection with the web server hosting www.google.com. TCP/IP is a set of protocols that allows computers to communicate over the internet. TCP ensures reliable, ordered, and error-checked delivery of data between devices, while IP handles the routing of packets across networks.

First, a TCP handshake takes place. Your browser sends a SYN (synchronize) packet to the web server, which responds with a SYN-ACK (synchronize-acknowledgement) packet. Your browser then sends an ACK (acknowledgement) packet to the web server, establishing a connection.

Once the TCP connection is established, your browser can send an HTTP request to the web server, requesting the webpage at https://www.google.com. This request and subsequent data exchange occur within the established TCP connection, ensuring reliable communication between your browser and the web server.

3. Firewall

Before the HTTP request reaches the web server, it may pass through a firewall. A firewall is a network security device that monitors and filters incoming and outgoing network traffic based on predetermined security rules.

The firewall ensures that only authorized traffic is allowed to reach the web server, protecting it from potential threats and attacks. It may inspect the HTTP request and block any suspicious or malicious requests.

4. HTTPS/SSL

When you enter https://www.google.com, the 'https' in the URL indicates that you are using the HTTPS (Hypertext Transfer Protocol Secure) protocol. HTTPS adds an extra layer of security to the communication between your browser and the web server.

The HTTPS protocol uses SSL (Secure Sockets Layer) or TLS (Transport Layer Security) to encrypt the data transmitted between your browser and the web server. This encryption ensures that the data cannot be intercepted or tampered with by unauthorized parties.

During the establishment of the TCP connection, your browser and the web server perform an SSL/TLS handshake. This handshake involves exchanging digital certificates to verify the authenticity of the web server and establish an encrypted connection.

What is an SSL Certificate?

An SSL server certificate is a digital certificate issued to the server for two main purposes:

1. To authenticate the server’s identity
2. To create a secure communication channel with the client.

The SSL server certificate uses public key infrastructure (PKI) to maintain the integrity and confidentiality of the data. It consists of a public and private key pair. The private key is stored on the server, whereas the public key is bundled together with the certificate and shared with the client during the SSL handshake. Once the certificate is installed on the web server, it switches the protocol to HTTPS, and the secure padlock symbol appears on the site.

5. Load Balancer

In order to handle a large number of requests and distribute the load evenly, popular and large websites like www.google.com often use load balancers. A load balancer acts as a traffic manager, distributing incoming requests across multiple web servers.

When your HTTP request reaches the load balancer, it determines which web server to send the request to based on various factors such as server availability, server load, or geographic proximity. The load balancer helps ensure that the web servers can handle the incoming requests efficiently and prevent overload.

6. Web Server

Once the HTTP request reaches the web server, it can process the request and generate a response. The web server is responsible for hosting the website and serving the requested webpages or resources.

The web server receives the HTTP request, retrieves the requested webpage or resource from its storage, and sends back an HTTP response to your browser. The response includes the requested content, such as HTML, images, CSS, or JavaScript files.

The web server often interacts with a database to provide dynamic content and personalized experiences to users. A database stores and organizes data in a structured manner, allowing the web server to efficiently retrieve and manipulate information.

Web Server vs. Application Server

In some cases, the web server may need to communicate with an application server to process dynamic content or perform specific tasks. An application server is a server specifically designed to run applications and handle the business logic of a website or web application.

For example, if you perform a search on www.google.com, the web server may send the search query to an application server, which processes the query, retrieves the relevant search results from a database, and sends them back to the web server. The web server then includes the search results in the HTTP response sent to your browser.

Response

After the HTTP request successfully reaches the web server, the server processes the request according to the specified URL and any additional parameters. This processing may involve fetching data from a database, executing server-side scripts, or accessing files stored on the server's filesystem. Once the server has gathered all the necessary resources and completed any required computations, it constructs an HTTP response to send back to the client's browser. This response typically includes a status code indicating the success or failure of the request (e.g., 200 OK for a successful request, 404 Not Found for a missing resource), along with any requested content, such as HTML pages, images, or other media files. The web server then transmits this response back to the client, completing the request-response cycle and enabling the user to view the requested content in their browser.

Conclusion

To sum up, from the initial URL input to the retrieval of web content, a symphony of processes unfolds seamlessly behind the scenes. URL aliasing fills in missing components, while DNS resolution maps human-readable addresses to machine-understandable IP addresses. TCP/IP connections establish reliable data exchange, fortified by firewalls and HTTPS/SSL encryption for security. Load balancers ensure even distribution of traffic, optimizing performance, while web and application servers handle requests and serve dynamic content. This intricate dance culminates in the seamless delivery of the internet's vast array of resources, all at the mere touch of a button.