Packet from Your Home to Google and Back

prerequisite is 1st understand Important networking concept for this work flow

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Step 1: You Type google.com

It all starts with a simple action. You open your browser and type google.com. Your computer now knows its ultimate destination by name, but it doesn't yet know its address in the language of the internet.

Copy Destination: google.com    

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Step 2: DNS Resolution

Computers don't use human-readable names like google.com; they use numerical IP addresses. To find the correct address, your computer performs a DNS (Domain Name System) lookup. It's like looking up a name in the world's biggest phone book.

Your computer sends a DNS request to a DNS server (often provided by your ISP or a public one like 8.8.8.8).

CopyAsks: "What is the IP address for google.com?"
DNS server replies: "google.com is at 142.251.220.46"

Now your computer has the specific address it needs to send the packet.

CopyDestination IP: 142.251.220.46    

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Step 3: Is Google on My Local Network?

Before sending the packet out, your computer does a quick check: Is this destination IP address part of my local home network?

Copy      Is 142.251.220.46 in my local network range (e.g., 192.168.x.x)?
   

The answer is no. Google's servers are not in your living room. This means the packet can't be sent directly. It must first be sent to the device that connects your home to the outside world: your router.

Computer's thought process: "This is an external address. I have to send it to my default gateway (my router) at 192.168.0.1."

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Step 4: Find the Router's MAC Address via ARP

To send anything to another device on the same local network (in this case, from your computer to your router), your computer needs its physical hardware address, known as a MAC address.

If your computer doesn't already know the router's MAC address, it shouts out a request on the local network using the Address Resolution Protocol (ARP).

CopyARP Request: "Who has the IP address 192.168.0.1? Tell me your MAC address!"

Router's Reply: "I have 192.168.0.1. My MAC address is 00:1a:2b:3c:4d:5e."

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Step 5: Build the Ethernet Frame

Now your computer has all the information it needs to construct the packet for the first leg of its journey. It builds an Ethernet frame containing two layers of addressing:

This frame is then sent over your Wi-Fi or Ethernet cable to your router.

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Step 6: The Router Works its Magic (NAT)

The router receives the frame. It sees the destination IP is outside the local network, so it knows its job is to forward it. But it can't send your private IP address (192.168.0.10) onto the internet.

This is where Network Address Translation (NAT) comes in. The router:

1. Strips off the Layer 2 MAC address information.

2. Replaces your private source IP (192.168.0.10) with your home's single public IP address (e.g., 122.56.77.88).

3. Picks a random source port (e.g., 54321) to keep track of your specific request.

4. Stores this translation in its NAT table so it knows where to send the reply later.

Copy
192.168.0.10:12345  <--->  122.56.77.88:54321

Finally, the router wraps this modified IP packet in a new frame and forwards it to the next router on the path—the one at your Internet Service Provider (ISP).

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Step 7: The Packet Travels Across the Internet

From now on, the journey is all about IP addresses. MAC addresses are only used for single hops between adjacent routers.

The packet, now with your public IP as its source, travels from router to router across the globe.

Copy      // Packet flying across the internet
IP Source: 122.56.77.88 (Your Home)
IP Destination: 142.251.220.46 (Google)
    

Each router on the path reads the destination IP address and consults its own routing table to decide the most efficient next hop to send the packet to. This could take it through multiple countries and networks in milliseconds.

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Step 8: The Packet Reaches Google

Finally, the packet arrives at a Google data center. Google's server receives the request. It sees the request came from your public IP (122.56.77.88) on port 54321.

It processes the request and prepares an HTTP response (the HTML, CSS, and JavaScript for the Google homepage). It then creates a reply packet.

CopyIP Source: 142.251.220.46 (Google)
IP Destination: 122.56.77.88:54321 (Your Home)

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The Return Journey: Google's Response Arrives Home

Step 9: The Reply Comes Back to Your Router

The reply packet travels back across the internet, routed directly to your home's public IP address. Your router receives a packet addressed to 122.56.77.88 on port 54321.

The router immediately checks its NAT table to see who this packet belongs to.

Copy"Aha! Port 54321 maps back to the device at 192.168.0.10 on its original port 12345."
 

The router now knows exactly which device inside your home to send the response to.

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Step 10: Find Your Device’s MAC via ARP (Again)

Just like before, the router needs your computer's MAC address to deliver the packet locally. If the entry has expired from its ARP cache, it will send out another ARP request.

CopyRouter's ARP Request: "Who has the IP address 192.168.0.10? Tell me your MAC!"

Your Computer's Reply: "I have 192.168.0.10. My MAC address is a1:b2:c3:d4:e5:f6." 

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Step 11: Router Builds the Final Ethernet Frame

The router now performs the reverse of NAT and builds the final frame for local delivery:

It sends this final frame to your computer over Wi-Fi or LAN.

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Step 12: Your Device Receives It!

Your computer's network card receives the frame.

Computer's thought process: "This frame's destination MAC address is mine, I'll accept it. The IP packet inside is from Google. Time to give this data to the web browser!"

Your browser receives the data, renders the HTML and CSS, and the Google homepage finally appears on your screen.

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Summary: The Two-Way Trip at a Glance

This whole process happens for every single resource—every image, script, and style file—needed to load a webpage. Here’s a simplified table of the journey.