An NSX-T logical switch reproduces switching functionality, broadcast, unknown unicast, multicast (BUM) traffic, in a virtual environment completely decoupled from underlying hardware.
Logical switches are similar to VLANs, in that they provide network connections to which you can attach virtual machines. The VMs can then communicate with each other over tunnels between hypervisors if the VMs are connected to the same logical switch. Each logical switch has a virtual network identifier (VNI), like a VLAN ID. Unlike VLAN, VNIs scale well beyond the limits of VLAN IDs.
When you add logical switches, it is important that you map out the topology that you are building.
For example, the topology shows a single logical switch connected to two VMs. The two VMs can be on different hosts or the same host, in different host clusters or in the same host cluster. Because the VMs in the example are on the same virtual network, the underlying IP addresses configured on the VMs must be in the same subnet.