Summary of What happens when you type a URL into your browser

## Understanding Web Page Retrieval When you type a website address into your browser and hit Enter, a hidden dance of technologies begins. This process, seemingly instant, involves multiple layers of internet protocols working together to fetch and display the web page you requested. Understanding these steps is fundamental to grasping how the internet functions and how web applications deliver content to users. ### 1. Parsing the URL: Deconstructing the Web Address The very first action your web browser takes is to break down the **Uniform Resource Locator (URL)** you've entered. Think of a URL as a complete address that tells the browser exactly where to find a resource on the internet and how to get it. For example, consider the URL `https://www.example.com/path/to/page.html`. Let's break down its components: * **Scheme (Protocol)**: `https://` specifies the communication method, in this case, Hypertext Transfer Protocol Secure. This tells the browser *how* to talk to the server. * **Domain Name**: `www.example.com` is the human-readable name for the web server. This is like the street name of a house. * **Port (Optional)**: This is a specific number that identifies a particular application or service on the server. For `https`, the default port is $443$, and for `http`, it's $80$. If specified, it would look like `www.example.com:8443`. * **Path**: `/path/to/page.html` indicates the specific file or resource you want to access on that server. This is like the house number and apartment number. * **Query String (Optional)**: `?name=value` are parameters sent to the server, often used to pass data, such as search terms or user preferences. For instance, `?search=web+page`. * **Fragment (Optional)**: `#section` is an internal anchor within a document, telling the browser to jump to a specific part of the page after it's loaded. > ### Definition: Uniform Resource Locator (URL) > A **URL** is a specific character string that constitutes a complete reference to a resource on the World Wide Web. The browser primarily extracts the **domain name** from the URL to figure out which server to contact. The other parts become relevant once contact is established. Did you know that the very first URL ever created was `http://info.cern.ch/hypertext/WWW/TheProject.html` by Tim Berners-Lee in $1990$? ### 2. DNS Lookup: Finding the Server's IP Address While humans use easy-to-remember domain names like `www.example.com`, computers and network devices communicate using **Internet Protocol (IP) addresses**, which are numerical labels. Think of an IP address as a phone number for a server (e.g., $192.0.2.1$ for IPv4 or $2001:0db8::1$ for IPv6). The **Domain Name System (DNS)** acts as the internet's phonebook, translating those human-readable domain names into machine-readable IP addresses. > ### Definition: Domain Name System (DNS) > The **DNS** is a hierarchical and decentralized naming system for computers, services, or any resource connected to the Internet or a private network. It translates domain names into numerical IP addresses. Here's how a typical DNS lookup unfolds: 1. **Browser Cache**: Your browser first checks its own temporary storage (cache) to see if it has recently looked up this domain name. If it finds the IP address, it uses that and skips the rest of the steps. 2. **Operating System (OS) Cache**: If the browser's cache doesn't have it, the browser asks your computer's operating system (OS). The OS also maintains a cache of recently resolved domain names (e.g., in a `hosts` file or its DNS client cache). 3. **Router Cache**: If your OS doesn't have the IP address, the request is sent to your local router, which often has its own DNS cache. 4. **Recursive DNS Resolver**: If the router can't provide the IP, the request goes to a specialized server called a **recursive DNS resolver**. This resolver is usually provided by your Internet Service Provider (ISP). 5. **Recursive Query Process**: The