How The Internet Connects
Summary: The internet is not one network but millions of separate networks linked by routers. Switches move traffic inside one network; routers forward it between networks one hop at a time until it reaches its destination.
At a glance​
| Question | Answer |
|---|---|
| What is it? | The chain of devices and links that carries data between machines |
| Why does it matter? | Explains what each box does and how traffic finds its way |
| When do I use it? | Reasoning about home networks, cloud networking, or where a connection breaks |
Building blocks​
| Piece | What it does |
|---|---|
| Network | A group of devices connected so they can exchange data |
| Cable | The simplest connection: one wire between two devices |
| Switch | Connects many devices inside one network and directs traffic between them; unaware of other networks |
| Router | Connects different networks and forwards traffic from one toward another |
| Routing table | The router's list of which next hop moves traffic closer to each destination network |
| Wi-Fi | A wireless replacement for the last short cable, using radio waves |
| Access point | Translates between the wired network and radio so wireless devices can join |
How it works​
- A router doesn't know the full path, only the next hop. Each router along the way makes its own next-hop decision.
- The internet is those hop-by-hop decisions repeated across millions of independently run networks.
- Switches identify devices by MAC address; routers forward traffic by IP address.
- A home "router" is usually a router, switch, and access point in one box.
- Between cities and continents, the backbone is physical fiber-optic cable, including cables laid on the ocean floor.
Why it feels instant​
- Fiber carries data as pulses of light. In glass, light travels at roughly two-thirds of its vacuum speed, about 200 km per millisecond.
- 10,000 km of fiber therefore costs about 50 ms one way.
- Each router hop usually adds well under a millisecond when the link isn't congested.
- Even dozens of hops across an ocean and back typically total tens to a couple of hundred milliseconds.
Remember​
- Switch = inside one network; router = between networks.
- Routers know the next hop, not the whole route.
- Over long distances, travel time through fiber usually matters more than hop count.
Related notes​
- IP Addresses And NAT - how devices are addressed
- DHCP Address Assignment - how devices get a local address