A vSphere Distributed Switch (dvSwitch or vDS) is the second type of software switching construct that can be used in a vSphere environment. Unlike a vSphere Standard Switch (vSS), which needs to be managed on a per-host basis, the vDS is managed at the vCenter layer. This, however, doesn't change the way ESXi handles network I/O.
A vDS is often misconceived as a single virtual switch spanning multiple ESXi hosts. One of the reasons for this misconception is that it is commonly documented as a data center-wide vSwitch. In essence, it is only the management plane of the vDS that creates this illusion. VMware still uses an individual data plane (hidden virtual switches) on each ESXi host. It is called a distributed switch since the management plane and the data planes that are distributed on the ESXi hosts are treated...