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Commonly confused · Routing & Switching

VLAN vs Subnet: What's the Difference?

A VLAN is a Layer 2 construct that divides a switch into separate broadcast domains. A subnet is a Layer 3 division of an IP address range. In good designs they map one-to-one, but they are separate concepts configured in different places.

VLANSubnet
OSI layerLayer 2Layer 3
Defined byVLAN ID (1-4094) on switch portsNetwork address and mask
Configured onSwitchesHosts, routers, DHCP scopes
SeparatesBroadcast domainsIP address ranges
Communication betweenRequires a router or Layer 3 switchRequires a router or Layer 3 switch
Typical mappingOne VLAN per subnetOne subnet per VLAN
Remember it

A VLAN draws walls on the switch; a subnet draws walls in the address book.

Exam tip

Questions ask what is required for two VLANs to communicate (inter-VLAN routing via router-on-a-stick or SVIs). Know that putting hosts in the same VLAN but different subnets breaks direct communication.

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