As you start working with Hyper-V, virtual networking configuration becomes very important.  You need to understand how to allocate physical adapters for use by Hyper-V (virtual switches) and what the difference is between an Internal, Private and External switch.  In Part 9 of the blog series, Tommy Patterson takes some time to explain the basics of Virtual Networking In Windows Server 2012 Hyper-V.

I am including a quick snippet from Tommy’s blog post below, but you will want to read the full article by going directly to his post.


Our blog series on virtualization has gotten off to a good start. For today’s article we discuss network virtualization in Windows Server 2012 Hyper-V. For the basics, virtual machines need to be presented with a network port in order to gain access to the physical network. Since the host has a small number of physical network adapters the hypervisor(Hyper-V) needs to split up the network traffic on to virtual network switches. These virtual switches contain virtual ports, and the virtual ports show up in each virtual machine for which they are assigned as a traditional network adapter. The diagram below shows this connectivity:

Now before we start deploying virtual switches in the production environment, let’s first take a step back and think through how best to insure our network is fault tolerant. New in Server 2012 is the capability to team physical network ports together. By this process, we are able to bind two physical network card ports together forming a an aggregation point for the network traffic which allows for failover ability in the event of a physical network failure. To access the NIC Teaming wizard, open Server Manager, in the navigation pane click on the Local Server. In the Properties area, click on NIC teaming. Here the available network ports are displayed and the administrator is allowed to select which ports will be part of the new aggregate.

There are two modes for NIC teaming: Switch Independent and Switch Dependent.

Switch Independent – In this mode, the network connections are physically attached to different switches on the network providing alternative routes for the traffic. This type of network team can be setup in two different ways. Active/Active or Active/Standby are the titles for these two different options. In Active/Active mode each network port is live and the traffic is balanced across the available ports. This allows for higher bandwidth as well as fault tolerance, as a network port can fail without disrupting traffic, however when less network pipes are available during a failure then less bandwidth is available as well. In Active/Standby mode one port is configured as the primary port for traffic, the secondary port is standing by ready to work in the event the first port fails. Bandwidth on the Active/Standby configuration stays constant in that only a single connection is live at any one point in time.

Switch Dependent – All of the network ports are physically connected to the same switch. This is a more traditional method for aggregating links together on to one physical switch, and supports Link Aggregation Control Protocol(IEEE 802.3ax) however using LACP is optional and requires the physical switch to support the protocol as well. A generic mode for balancing the traffic is utilized by default should the LACP protocol not be enabled.

A couple of important notes concerning NIC Teaming as pertains to the virtual infrastructure. If the traffic is made up of large TCP sequences, for example a Hyper-V Live Migration or Shared Nothing Live Migration, only one port is utilized in the team for the traffic. This cuts down on the amount of retransmits that would occur as packets may arrive out of order on the receiving end of this high speed network discussion if more than one port were utilized. Hyper-V takes care of this for you.

Now that we understand the principals of the physical network stack let’s talk through the basic options available for the virtual network stack.

Virtual Network Options

In Hyper-V Manager we will take a look at the Virtual Switch Manager and setup a new virtual switch:

Notice that we have three options available to us: External, Internal, and Private. Let’s talk through each of these choices first.

External – For network traffic that will be destined to the physical switches in the server’s location. This is the switch type most commonly used in production environments to serve data for end users and other server systems on the network.


Harold Wong