Consider following situation:
10.3.0.0/16 network without any VLANs. Now You want to divide it...
You want Your IT department be able to reach the entire network, but sales department only Domain Controller, printers etc. You want IP cameras would be reachable only by security and managers.. I think You've got the idea.
Question: Am I getting it right that it is not possible that all hosts stay in same subnet, but each host will now belong to some VLAN, and the "routing" between VLANs will be done via Layer 3 switches. If not how it can be done?
P.S. I know that it can be done if You divide
10.3.0.0/16 to smaller subnets.