vSwitches operate at the VMkernel layer. Unlike most of the physical switches in a modern environment, a vSwitch is not a managed switch. However, it does know the MAC addresses of the virtual machine adapters mapped to it.
By default, a vSwitch—vSwitch0—is created during the ESXi installation.
To manually create a new vSwitch, you can use the vSphere Web Client GUI, the vSphere Windows Client GUI, or the esxcfg-vswitch command.
There is one fundamental difference in the process of creating a vSwitch using the esxcfg-vswitch command. Unlike the Add Networking wizard, which requires you to create a port group to proceed with the creating of the vSwitch, the esxcfg-vswitch command lets you create a vSwitch with no port groups and with no uplinks.
When a vSwitch is created it will have 128 ports by default. The number of ports per vSwitch is configurable up to a maximum of 4096 ports.