Unlike just about every other Cisco physical switch, the Cisco's Nexus 1000-V is a virtual software switch. This switch is custom made for VMware vSphere and it is the only 3rd party switch for vSphere. While there is a free 60 day eval of vSphere and the Nexus 1000-V, to use them for the long run, you'll have to buy the highest edition of vSphere - Enterprise Plus - and the Nexus 1000-V, both of which are based on the number of CPUs your servers have which will run the 1000-V.
With the Nexus 1000V (N1KV), you get the Cisco IOS command line (actually NX-OS) for your virtual infrastructure, policies, QoS, Security, and many other Cisco switch featuers that you (or your network admin) are used to using. VMware's dvSwitch and the Cisco Nexus 1000V make a powerful team but you mut also know how to install it, add ESX hosts to the new switch, and create port profiles.
Once you already have your vSphere infrastructure up and running and have met the prerequisites, you can start the install process for the Nexus 1000V. I'll warn you that there is a lot more to it than, say, just installing a new Windows app. The install is detailed in the 44 page installation guide for the Nexus 1000-V. Luckily, VMware VCP and VCDX Rick Scherer has created a new video series on the Nexus 1000-V.
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