The Lazy Networker

When your PC communicates with Google’s server (e.g., http://www.google.com), there’s a sequence of events happening from your local network to Google’s global infrastructure.

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🧩 Step-by-Step Communication Flow

1️⃣ You type “http://www.google.com” in your browser

Your browser doesn’t know where Google is yet—it only has a domain name.

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2️⃣ DNS Resolution (Finding the IP Address)

• Your PC asks the DNS resolver (usually your ISP’s DNS or a public one like 8.8.8.8) to find the IP address of http://www.google.com.
• The resolver checks:
  1. Local DNS cache (in your PC or router)
  2. If not found, it queries the root DNS servers
  3. Then .com TLD servers
  4. Finally Google’s authoritative DNS servers
• You get back an IP address, e.g. 142.250.193.68

🔸 Now your PC knows where to send packets — Google’s IP.

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3️⃣ ARP (Address Resolution Protocol)

Before sending packets out, your PC needs to know the MAC address of the next hop (usually your router).

• Your PC sends an ARP Request: “Who has the gateway IP (e.g., 192.168.1.1)?”
• The router replies with its MAC address.
• Now your PC can send the packet to the router.

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4️⃣ TCP Connection Establishment (3-Way Handshake)

Your PC establishes a TCP connection with Google’s server (port 443 for HTTPS):

1. SYN → Client → Server (request to start session)
2. SYN-ACK ← Server → Client (acknowledge and agree)
3. ACK → Client → Server (final confirmation)

✅ Connection established.

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5️⃣ TLS/SSL Handshake (Secure Encryption)

Since Google uses HTTPS, a TLS handshake occurs:

• Browser and server agree on encryption methods.
• Server sends its SSL certificate (issued by a trusted Certificate Authority).
• Browser verifies authenticity.
• A secure session key is generated.

🔒 Now communication is encrypted end-to-end.

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6️⃣ HTTP Request and Response

• Browser sends:
  GET / HTTP/1.1
Host: www.google.com
• Google server processes it and responds with:
  HTTP/1.1 200 OK
  (plus HTML, CSS, JavaScript, etc.)

The web page starts loading.

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7️⃣ Data Flow Path

• Your data packet flows through multiple layers:
  1. PC → Router (LAN)
  2. Router → ISP (WAN)
  3. ISP → Internet Backbone
  4. Internet → Google Data Center

Google uses CDNs (Content Delivery Networks) — your request is usually served from the nearest Google edge server, not necessarily the US.

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8️⃣ Response Rendered

Your browser receives the HTML and starts rendering the Google homepage with logo, search box, etc.

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🌐 Simplified OSI Model Mapping

OSI Layer	Example in this process
7 – Application	HTTP / HTTPS
6 – Presentation	SSL/TLS encryption
5 – Session	TCP connection management
4 – Transport	TCP (Port 443)
3 – Network	IP addressing and routing
2 – Data Link	Ethernet / Wi-Fi (MAC addresses)
1 – Physical	Cables, Wi-Fi signals, etc.