A network runs on physical devices, each with a clearly defined role within the OSI layers.

The key devices

• Switch — layer 2, it connects the hosts of a single LAN and forwards frames based on MAC addresses.
• Router — layer 3, it connects different networks and forwards IP packets between them.
• Access point — extends the network over Wi-Fi.

The cables

• Twisted-pair copper (UTP) — the classic RJ45, up to 100 m.
• Fibre optic — long distances and high bandwidth.
• Console cable — for managing a device directly.

On a Cisco switch you can display the state of the ports and the table of learned MAC addresses.

Switch> enable
Switch# show interfaces status
Switch# show mac address-table

The MAC table shows which device sits on which port: that is how the switch sends frames where they belong instead of flooding them everywhere.

Key point: the switch works at layer 2 (MAC), the router at layer 3 (IP). See Lab 3 – Cabling a simple network in Packet Tracer.