What Happens When You Type A URL Into The Browser

When you type a URL into your browser, a complex series of steps occurs behind the scenes to load the webpage. Here’s a breakdown of the process:

DNS Lookup: The browser checks its cache for the IP address of the domain. If not found, it queries DNS servers (root, TLD, and authoritative) to resolve the domain name to an IP address.
TCP Connection: The browser initiates a TCP connection with the server using a three-way handshake (SYN, SYN-ACK, ACK).
HTTP Request: Once connected, the browser sends an HTTP request to the server for the webpage.
Server Response: The server responds with the HTML document and linked resources (CSS, JavaScript, etc.).
Rendering: The browser processes the HTML, builds the DOM tree, and renders the page by executing JavaScript and painting the layout.

You Should Know:

Here are some practical commands and steps to understand and simulate parts of this process:

Use `nslookup` or `dig` to perform a DNS lookup:
```
nslookup example.com
dig example.com
```

Use `telnet` or `nc` (netcat) to test TCP connections:
```
telnet example.com 80
nc -vz example.com 80
```

Use `curl` to send an HTTP request and view the response:
```
curl -I http://example.com
```

Use `tcpdump` or `Wireshark` to capture and analyze network traffic:
```
sudo tcpdump -i eth0 port 80
```

Open browser developer tools (F12) to inspect network requests, DOM tree, and rendering performance.