Here is the OS + network + application communication when make a request by typing “google.com”

1. You press keys

• When you type “g”, “o”, “o”… your keyboard sends electrical or touch signals to the computer.

• The OS detects each keypress, and the browser shows it in the address bar while suggesting completions like google.com.

• When you hit Enter, another signal is sent — the OS delivers a key event to the browser.

2. The browser parses the input

• The browser checks if what you typed is a valid URL or just a search term.

• Seeing google.com, it treats it as a domain name.

• If https:// isn’t typed, it checks if the site is on the HSTS list (always use HTTPS). For Google, it is — so the browser prepares an HTTPS request.

3. DNS lookup

• The browser looks in its cache to see if it already knows the IP address of google.com.

• If not, it asks the OS, which may check:

  • The hosts file

  • The local DNS cache

  • Your configured DNS server (often your router or ISP)

• If necessary, DNS servers on the internet are queried until the IP is found

4. ARP (finding the next hop)

• Before sending the DNS query or HTTP request, your computer must know the MAC address of the next device (router/gateway).

• If it doesn’t, it sends an ARP request on the network asking, “Who has this IP?” and receives a reply with the MAC address.

5. TCP connection setup

• The browser opens a socket to the server’s IP on port 443 (HTTPS).

• A TCP three-way handshake happens:

  1. Client → Server: SYN

  2. Server → Client: SYN + ACK

  3. Client → Server: ACK

• This establishes a reliable connection.

6. TLS handshake

• To create an encrypted connection:

1. Browser sends a ClientHello with supported ciphers.

2. Server replies with a ServerHello and its certificate (with its public key).

3. Browser verifies the certificate, then sends a random secret encrypted with the server’s public key.

4. Both sides use this secret to create a shared session key.

• All communication is now encrypted.

7. HTTP request

7.1. Request

GET / HTTP/1.1
Host: google.com

7.2. Response

200 OK
[headers]
[HTML content]

7.3. Browser rendering

1. HTML parser builds the DOM tree.

2. CSS files are fetched and parsed into a Style Tree.

3. JavaScript is executed (which can modify the DOM).

4. The browser constructs a Render Tree → calculates layout → paints pixels to the screen.

5. The GPU helps compose and display the final image.

7.4. After load

• JavaScript continues running (for example, showing animations or handling user input).

• Additional network requests (images, CSS, JS files) are made as needed.

• The page becomes interactive, and you can start typing your search.

8. Dive deep

8.1. What is different from MAC, IPv4, IPv6

8.1.1. IP = Global routing

• Routers use IP addresses to move data between networks.

• Example: from your home network → your ISP → Google’s data center.

8.1.2. MAC = Local delivery

• On each local network (like your home Wi-Fi), devices don’t understand IP directly.

• They use MAC addresses to actually deliver packets from one network card to another.

8.1.3. ARP Protocol (IP -> Mac)

• The OS uses ARP (Address Resolution Protocol) to map IP → MAC before sending data.

8.1.4. IPv4, IPv6, A and AAAA records

When you access https://google.com:

1. Your computer asks DNS for the IP:

• A record → IPv4 address

• AAAA record → IPv6 address

1. If your network supports IPv6, your OS/browser prefers IPv6 (modern default).

2. If not, it falls back to IPv4.

➡️ Result: both IPv4 and IPv6 users reach the same website, just over different network paths.

Notes: If you want to use IPv6, you need to config the router to allow IPv6.

8.2. IP and MAC Address

• IP: find the location and address.

• MAC: where you transfer data, by binary to a router.