How the Internet Works

How the Internet Works

IP Addresses, Routers, DNS, and the Packet Journey

You type "www.google.com" into your browser, press Enter, and within a second, a page appears. That simple action triggers a complex chain of events involving billions of devices worldwide. In this post, we will strip away the magic and explain the fundamental building blocks of the Internet.

1. The Internet Is a Network of Networks

The Internet is a collection of connected networks. Your home network connects to your ISP. Your ISP connects to larger regional networks, which connect to backbone providers that span continents.

Analogy: The Internet is like the global road system. Your home connects to a local street, which connects to a highway, which connects to interstate highways, and finally to the destination's driveway.

Key point: No single company owns the Internet. It is a cooperative system of thousands of networks (Autonomous Systems – ASes) that agree to exchange traffic using standard protocols.

2. IP Addresses – The Postal Address of the Internet

Every device connected to the Internet needs a unique identifier: an IP address.

The world ran out of IPv4 addresses in 2011. IPv6 solves this, but adoption is gradual.

Public vs. Private IP: Your router has one public IP (globally unique, assigned by your ISP). Your phone has a private IP (e.g., 192.168.1.5) behind the router. When you visit a website, the website sees your router's public IP, not your phone's private IP.

3. Routers – The Traffic Directors

A router connects different networks and forwards data between them. It examines the destination IP address of every data packet, looks up its routing table to decide which direction to send the packet, and forwards it one hop closer to its destination.

Analogy: A router is like a postal sorting facility. It reads the address on each letter and decides which truck (next hop) should carry it.

4. Packets – The Envelopes of the Internet

Data is broken into small chunks called packets (typically 1,500 bytes or less). Each packet contains a header (source IP, destination IP, sequence number, error-checking data) and a payload (the actual piece of data).

Why packets? Efficiency (if a packet is lost, only that packet is resent), shared infrastructure (many users can send packets interleaved), and error resilience (packets can take different routes if some links fail).

Analogy: Sending a book as a series of numbered postcards. They may arrive out of order, but the receiver reassembles them correctly.

5. DNS – The Phonebook of the Internet

Humans remember names (google.com), but computers need IP addresses (142.250.190.46). DNS translates domain names to IP addresses.

1. Your browser checks its local cache.
2. If not found, it asks your operating system (which has its own cache).
3. If still not found, your computer sends a DNS query to a DNS resolver (usually your ISP or a public service like 8.8.8.8).
4. The resolver queries multiple DNS servers (root servers, TLD servers, authoritative nameservers).
5. The resolver returns the IP address to your browser.
6. Your browser makes a connection to that IP address.

Security note: Traditional DNS is unencrypted – an attacker on your network can see which websites you visit. DNS over HTTPS (DoH) and DNS over TLS (DoT) encrypt these queries.

6. The Journey of a Packet – A Concrete Example

Let us follow a packet from your laptop (192.168.1.5) to a web server (93.184.216.34 – example.com).

1. Your laptop: The browser generates an HTTP request. Your laptop sends it to your default gateway (your router, usually 192.168.1.1).
2. Home router: Performs NAT – replaces your private IP with its public IP (e.g., 203.0.113.8) and remembers the mapping. Forwards the packet to your ISP.
3. ISP routers: The packet hops through several routers within your ISP's network, each consulting its routing table.
4. Internet backbone: The packet moves through tier-1 backbone providers (Level3, Cogent, etc.), possibly via undersea cables, using BGP (Border Gateway Protocol).
5. Destination server: The server processes the HTTP request and sends back a response packet following the reverse path.

Total time: Typically 20–100 milliseconds. Each "hop" adds a few milliseconds.

7. TCP and UDP – Reliable vs. Fast Delivery

Summary

Review Questions

1. What is the difference between a public IP address and a private IP address?
2. Why does the Internet break data into packets instead of sending whole files as a stream?
3. If your browser cannot reach "www.example.com" but you can ping "93.184.216.34" (the server's IP), what is likely broken?