The network stack: why layers exist
How a message becomes a frame and back again, and how layers turn "the internet is broken" into a solvable problem.
Sending "hello" to another machine is really dozens of decisions: which program gets it, how to find the machine, what to do when a cable drops a signal. If every app had to solve all of them, the internet would be impossible. Layers split those decisions: each one solves a single problem and trusts the layer below.
Four layers carry you from a click to a wire. Application: what you actually mean (HTTP, DNS, SMTP). Transport: which program on the machine and whether delivery is guaranteed (TCP, UDP, ports). Internet: how to find the machine anywhere on the planet (IP addresses, routing). Link: how to move bytes across one physical hop (Ethernet, Wi-Fi, MAC addresses).
Приложение "привет" <- данные
Транспорт [TCP | порт 443 | привет] <- сегмент
Сеть [IP | 93.184.216.34 | TCP | порт 443 | ...] <- пакет
Канальный [Ethernet | MAC роутера | IP | TCP | ...] <- кадр
На каждом слое добавляется свой заголовок.
Получив кадр, приёмник снимает заголовки в обратном порядке.Practice
Order the layers as a message travels down from your application to the wire.
Hints
- Start with what a human creates: text, a click, a request.
- A port is transport, an IP address is internet, a MAC address is link.
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Match each layer with what it is actually responsible for.
Hints
- An IP address does not guarantee delivery — it only says where to go.
- DNS and HTTP are things the application itself does, not the network.
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A packet leaves your laptop for a server in another country. Which device decides which neighbour the packet goes to next?
Hints
- Think about who chooses the next hop for the packet.
- A switch only works inside one local network segment.
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