VLAN

Problem

Accounting and guest Wi-Fi use the same physical switches. But you don't want them to behave as one local Ethernet network. Buying completely separate switches and cabling for every network would be wasteful.

Solution — VLAN

A switch can maintain multiple logically separate Ethernet networks on the same physical infrastructure.

VLAN 10 → Employees
VLAN 20 → Guests
VLAN 30 → Servers

Core idea: VLANs create separate logical LANs over shared switching infrastructure.