VLANs create separate broadcast domains at Layer . Devices in different VLANs cannot communicate without a Layer device to route between them.
main approaches for inter-VLAN routing:
Router on a Stick: A single router interface connects to the switch as a trunk. The router creates subinterfaces for each VLAN.
Layer Switch: The switch itself performs routing between VLANs using SVIs (Switched Virtual Interfaces).
Without inter-VLAN routing, VLAN cannot reach VLAN even if they're on the same physical switch. Traffic must go up to Layer , be routed, and come back down to Layer .