Q: How do I use a logical network in System Center Virtual Machine Manager 2012?

A: There are three main steps to using a logical network. First, you need to actually create it:

  1. Start the Virtual Machine Manager 2012 administration tool.
  2. Open the Fabric workspace.
  3. Navigate to Networking, Logical Networks.
  4. Create a new Logical Network using the Create Logical Network action.
  5. Give a name and description for the new logical network, and click Next.
  6. The next step is to create sites that represent the logical network. A site consists of VLAN and subnets that are written in the CIDR format (e.g., for network with a subnet mask of You would add sites for each location that this logical network exists at, such as all your data centers and the host groups that represent the network site. For example, if I had three data centers, I would add three sites, one for each data center, and set the IP subnet and VLAN ID for the network at each location.
  7. The IP subnet is optional, and you can use only the VLAN ID; or if you aren’t using VLANs, then set the VLAN to a value of 0, which disables VLAN. If you don’t specify an IP subnet and just specify the VLAN ID, then the virtual machines (VMs) will use DHCP to get IP addresses.
  8. Click Next. In the screen shot below, you can see for the London site that only a London host group can use it; for the Allen site, only the Allen host group can use it, and the same for New York. scvmm2012logicalnetwork1

  9. A summary is displayed, then click Finish.

After the logical network is created, IP pools are created for each site. These are IP addresses that can be given to the VMs when created in the various sites, acting like a mini DHCP service for the VMs. However, these VMs should be given fixed IP addresses, which are needed if the VMs are part of a load-balanced scenario.

  1. Select the logical network in the Virtual Machine Manager console and select the Create IP Pool action.
  2. Give a name and description for the new IP pool, and select the logical network the IP Pool will belong to. Click Next.
  3. Select the network site that this IP pool will be attached to (or you can create a new site). Click Next. (See screen shot below.)
  4. Specify the IP range that will be part of this pool. It’s also possible to reserve certain IP addresses from those ranges such as for load balancer Virtual IPs (VIP). Specify the required values, and click Next. (See screen shot below.)

  5. Specify the Gateway IP address and click Next.
  6. Enter the DNS servers and DNS suffixes and click Next.
  7. Enter WINS information (if any) and click Next.
  8. Click Finish on the Summary to complete the pool creation. (See screen shot below.) scvmm2012logicalnetwork4

Next, on the virtualization hosts you need to specify which NICs in the server have connectivity to the logical networks. You need to perform this on all the hosts in the various data centers that will have VMs deployed from the templates that use the logical network.

  1. In the Fabric workspace, navigate to Servers, .
  2. Select your virtualization host (such as your Hyper-V server), and open its properties.
  3. Select the Hardware node.
  4. Scroll down to the Network Adapters.
  5. Select the network adapter that you want to specify as connected to the logical network.
  6. Select the logical network in the available list. (See screen shot below.)
  7. You can also click the Advanced button on the NIC properties. It lets you configure the mode of the switch port the NIC is connected to (Trunk or Access) and also specify which IP subnets associated with the logical network should be used by this host (which should be set automatically based on the sites you previously created and the host groups the sites were associated with). The switch mode (Trunk/Access) is dependent on the configuration of the switch port your NIC is connected to and should match. Although Access mode is the default on physical switches, any VLAN IDs are stripped off the packets and the port is locked to a specific VLAN set on the port. This means the VLAN ID on the VMs and the virtual network must match or the traffic won’t have external host access. With Trunk mode, multiple VLAN IDs can share the same physical NIC and switch. Thus if you have multiple VLANs on a single NIC, then you need the physical switch port to be configured as Trunk mode and the VLAN IDs that will be supported on the port. (See screen shot at this link.)
  8. Click OK to all dialog boxes to complete the configuration.

Finally in the virtual machine (VM) template, specify the logical network for the connectivity.

  1. In the Library workspace, navigate to Templates, VM Templates.
  2. Select the properties of the template.
  3. Select the Hardware Configuration node.
  4. Select the Network Adapter, and under connectivity select the logical network that was created and click OK. See screen shot below. 

Your environment is now set up for logical network use!


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