Ethernet

Problem

You have several computers in the same local network. Computer A has some bytes for Computer B. But a cable or Wi-Fi network is just a shared communication medium. How does A specify which local device should receive its data?

Solution — Ethernet

Ethernet gives network interfaces MAC addresses and wraps data into frames containing source and destination MAC addresses.

A                    B
AA:01 → Ethernet → BB:02

A switch reads the destination MAC and forwards the frame toward B.

Core idea: Ethernet provides local delivery between network interfaces.