VLAN vs subnet: what is the difference?
A VLAN and a subnet solve related problems at different layers. A VLAN separates traffic at layer 2 (switching); a subnet separates addresses at layer 3 (routing). They are usually mapped one-to-one, but they are not the same thing.
The core difference
A VLAN (Virtual LAN) is a way to make one physical switch behave like several separate switches. Ports in different VLANs cannot see each other's broadcast traffic, even on the same hardware. It is a layer-2 concept: it works with MAC addresses and frames.
A subnet is a layer-3 concept: it is a range of IP addresses with a shared prefix. Hosts in different subnets need a router to communicate. Where a VLAN separates broadcast domains, a subnet separates address space.
Why they usually go together
In most designs, each VLAN maps to exactly one subnet. VLAN 10 might be 192.0.2.0/24, VLAN 20 might be 198.51.100.0/24. This pairing is clean: the VLAN keeps the traffic separate at layer 2, and the subnet gives that segment its own address range at layer 3, with a router interface as the gateway between them.
Keeping the mapping one-to-one makes the network easier to reason about. When you see VLAN 20, you know it is 198.51.100.0/24, and vice versa.
When they do not line up
You can run multiple subnets on one VLAN (secondary addressing) or, less commonly, stretch a subnet across VLANs with bridging. Both are edge cases that add complexity and are usually avoided. The takeaway: a VLAN is about isolating traffic, a subnet is about organising addresses, and good designs keep them aligned.
Frequently asked questions
Is a VLAN the same as a subnet?
No. A VLAN is a layer-2 broadcast domain; a subnet is a layer-3 address range. They are usually paired one-to-one, but they operate at different layers.
Can one VLAN have two subnets?
Yes, using secondary addressing, but it is uncommon and adds complexity. Most designs keep a single subnet per VLAN.
Do different subnets need different VLANs?
Not strictly, but pairing each subnet with its own VLAN is the standard, clean approach. It keeps broadcast domains and address ranges aligned.