Virtualization: Virtual Switch vs Physical Switch

Virtualization: Virtual Switch vs Physical Switch

Virtual Switch vs Physical Switch

Today let’s talk about the difference between the Virtual Switch and the Physical Switch. It’s not only about the physical and software switch comparison there is more to know. We’ll take VMware vSwitch as an example for virtual switch comparison.


Because a vSwitch is software-based, you have the flexibility to configure the same the way you want. I mean if you need more virtual ports to connect your Virtual Machine you can very much do that. However, it is not possible with a physical switch all you need to do is spend dollars to add a line card or add more switches to the network.

Layer 2 Switching Logic

vSwitch keeps its life simple and only knows about the Virtual Machines connected to the virtual ports. It has no knowledge about the hosts connected to the outside network. If it receives traffic for a host that is not listed in the MAC address table, it simply drops the traffic. There is no flooding mechanism vSwitch performs to know the unknown MAC address. It maintains the small MAC address table that holds the entries for virtual machines connected to the vSwitch.

If a virtual machine wants to communicate to the host in the outside world, it hands over the traffic to the uplink port.

Physical switches hold thousands of MAC address entries for hosts directly or indirectly connected. If a frame is received to forward traffic to an unknown unicast address, a physical switch performs the flooding to know the port that can send the traffic toward the host.


Figure 1: vSwitch L2 Forwarding Logic

Uplink Ports

vSwitch has one physical port which is called the uplink port. The uplink port is an entry or exit point for traffic from the outside world to the virtual environment and vice versa.

These uplinks ports are available on the bare metal server. All traffic that needs to go out is dependent on the uplink ports, that’s the reason it is recommended to have redundant uplink ports. Normally there are two ports that are connected to the physical switch in the network to provide high availability.

If you don’t want your virtual machines on the server to go outside the world, you don’t need an uplink port.

There are sometimes when one Virtual Machine wants to talk to another that is hosted on the same physical server, it does not use the uplink port. vSwitch is aware of both the VMs and just switches the traffic from one virtual port to another. This traffic is called “dark traffic” because it is difficult to track and monitor without modern virtualization monitoring and management tools. 

In the physical switch uplink known as the trunk port that is the connection between two switches. Uplink helps to expand the network.

Virtual Ports

A virtual switch can dynamically define the number of virtual ports. This dynamic nature of defining the required ports makes virtual switches agile and ports on demand for new virtual machines. These virtual ports provide connections to –

  • Virtual Machines NICs (vNIC) – vNIC as on virtual machine for network communications
  • VMkernel Ports – to handle system traffic such as vMotion, IP Storage, Fault Tolerance, vSAN and others.
  • Service Console – is the administrative interface that is used directly on the hardware.

I hope you find this informative!

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