Traffic between Virtual machines is not switched; it is routed by the standard vRouter included with ESXi

A standard or distributed vSwitch which comes with ESXi must be used, there is not 3rd party software available

A 3rd party virtual switch is required such as the CISCO Nexus 1000v as no standard vSwitch exists with ESXi

The included standard vSwitch of the CISCO Nexus 7000

The included standard vSwitch or the CISCO Nexus 1000v