A virtual switch is a software component of a virtual server, providing network connectivity to virtual machines (VMs). The challenge with virtual switches is integrating them into the rest of the network in order to maintain visibility and control.
The diagram shows how the emerging VEPA (Virtual Ethernet Port Aggregator) standard addresses this challenge by ensuring that packets from the virtual machines connected to the virtual switch (shown in green) also pass through an adjacent hardware switch (Bridge). In a blade server, the adjacent hardware switch would be the blade switch. If stand-alone servers are used, then the adjacent hardware switch would be the top of rack switch.
Passing traffic through the hardware switch offloads tasks such as rate limiting and access control lists (ACLs), simplifying the virtual switch and freeing CPU cycles that can be used by the virtual machines.
The sFlow standard is widely supported by switch vendors. Selecting blade switches and top of rack switches with sFlow and VEPA support will offer visibility and control of the network edge.