Most people think of the internet as a “cloud,” but for a System Design engineer, the internet is a series of physical wires and handoffs.

If you’ve never used a terminal or don’t know what a “Server” really is, this is the perfect place to start.

1. The Analogy: Sending a Letter

Imagine you want to send a letter to a friend in another city. You need three things:

  1. The Message: The content of your letter.
  2. The Address: Where is your friend’s house? (IP Address)
  3. The Courier: The system that moves the letter from your house to theirs. (The Internet)

In digital terms:

  • Your Letter is broken into small pieces called Packets.
  • Your Friend’s House is a Server.
  • The Address is a string of numbers like 142.250.190.46 (An IP Address).

2. IP Addresses: The GPS of the Internet

Every device connected to the internet—your phone, your laptop, even your smart fridge—has a unique address.

  • IPv4: The “classic” address (e.g., 192.168.1.1). It’s like a 10-digit phone number.
  • DNS (The Phonebook): Since humans aren’t good at remembering numbers like 142.250.190.46, we use DNS to map names like google.com to those numbers.

[!NOTE] DNS is like a contact list. You search for “Mom,” and your phone knows the number is 555-1234. You type google.com, and your browser finds 142.250.190.46.

3. The Journey of a Packet

When you click a link, your data doesn’t move as one giant chunk. It gets chopped up into Packets (usually about 1.5 KB each).

Step-by-Step:

  1. Chop: Your browser splits your request into 10 packets.
  2. Label: Each packet gets a “stamp” with your IP and the Server’s IP.
  3. Hop: Packets travel through Routers (sorting offices). One packet might go through New York, while another goes through Chicago.
  4. Reassemble: At the destination, the server waits for all 10 pieces and stitches them back together.

4. Why Does This Matter for Scaling?

If one “sorting office” (router) is busy, your packets get delayed. If a wire is cut, your packets must find a new route.

The Lesson for Beginners: The network is never 100% reliable. As designs get bigger, we have to assume that some “letters” will get lost or arrive late.

Beginner’s Checklist

  • Do I understand that an IP Address is just a location?
  • Do I understand that DNS is just a phonebook?
  • Do I understand that Packets are small chunks of a big message?

In the next chapter, we’ll look at Modern Networking Primitives, where we learn how to make these packets move faster and more reliably.