How do VLAN's work with subnets?

Question

I know how to subnet but I'm a bit confused when it comes to how VLAN's work within a network. Say i have 3 different groups of users, split on 2 different levels of a building.

Ground floor = 5 students, 5 teachers First floor = 5 students, 5 teachers

Logic tells me the ground floor would be on it's own subnet, same with the first floor. But I also want the students to be on their own VLAN, and the teachers on their own. How does this work if the ground and first floors have their own subnet? ie whole first floor = 10.1.1.2-12 and ground floor 10/1/2/2-12

Thanks in advance for any explanation or if I'm heading in the wrong direction

Answer 1

Depending on where you are in your University classes, there are three options.

If you have already covered "Layer 3 Switching", you could set up an SVI for the Students, and an SVI for the Teachers. Then the first floor and ground floor would only need a Layer2 path (aka through switches) to your Layer 3 switch. Then you could have these two VLANs existing at two different locations.

If you haven't already covered "Layer 3 Switching", and you are purely in a "Router L3" and "Switch L2" world, then unless you do something special (see below) you will probably need to use four different VLANs and four different IP Subnets: A Students 1st Floor, B Students Ground Floor, C Teachers 1st Floor, D Teachers Ground Floor.

You could get around that and (in a way) do a manual "L3 switch" by connecting your central router to a switch, and then that switch has a trunk to each of your "Floor" switches. You could then have one VLAN/IP Subnet for Teachers, and another for Students, and they could exist in two different locations.

Answer 2

There are exceptions, but generally speaking, there is a one-to-one match between VLANs and subnets. In other words, for every VLAN, you have a subnet, and vice versa. So you would have two subnets (and two vlans) on each floor -- one for students and one for teachers.