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Frequently Asked Questions: Virtual Networks in VMM

Updated: September 11, 2009

Applies To: Virtual Machine Manager 2008, Virtual Machine Manager 2008 R2, Virtual Machine Manager 2008 R2 SP1

How are network locations created, and can I change them?

For Windows-based computers in an Active Directory domain, network locations are automatically discovered as the Domain Location. For network adapters that are disconnected, are not connected to a domain, or are on a host that is not in a domain, the network location is empty. You can configure different network locations for physical network adapters on a host by configuring settings on the Hardware tab of the Host Properties dialog box or by using the Set-VMHostNetworkAdapter cmdlet with the –NetworkLocation parameter in the Windows PowerShell – Virtual Machine Manager command shell.

During virtual machine placement, how does VMM consider the networking needs of a virtual machine?

While creating or deploying a virtual machine, you can specify the network location to which to connect the virtual machine. During virtual machine placement, VMM checks the virtual machine’s networking requirements against the networks configured on all managed hosts. Any host that does not have a network adapter configured with the specified location receives a zero star rating.

If there is a port conflict, is it possible to change a P2V port number from the default value of TCP 443?

Yes. You can change the P2V port number by performing the following steps:

  1. Create the following registry key: HKLM\Software\Microsoft\Microsoft System Center Virtual Machine Manager Server\Settings\P2VBITSTcpPort.

  2. On the VMM server, type DWORD, and then enter the desired port number (a number less than 32768).

  3. Restart the Virtual Machine Manager service, and then try the P2V conversion again.

How is a private network different from an internal (host bound) network and an external network?

On a private network, the virtual machine can communicate with other virtual machines but not with the host or with external networks. On an internal (or host bound) network, virtual machines can communicate with each other and the host but cannot communicate with external networks because the network is not bound to a physical network adapter.

On an external network, which is bound to a physical network adapter, the host and its virtual machines can communicate with external computers. External networks can be bound to the host also by selecting the Host access option in the network configuration in the host properties (Networking tab). (In Windows PowerShell – VMM, this is the -BoundToVMHost parameter of the New-VirtualNetwork and Set-VirtualNetwork cmdlets.) If this property is selected, the virtual network has access to the host. If the property is not selected, virtual machines can communicate with external computers but not with the host.

Why can't I create a DHCP server for my Hyper-V virtual networks?

Virtual Server provides a DHCP server for virtual networks; Hyper-V does not. If you want a DHCP server on a Hyper-V host, one option is to create a virtual machine with Windows Server configured to provide the DHCP service and then add the virtual machine to the virtual network.

What is the support for virtual networks on VMware ESX Server hosts?

When you use VMM to manage ESX Server hosts, you can create virtual networks (known in VirtualCenter as virtual switches) on the host and connect the virtual networks to virtual network adapters. However, you cannot create console ports in VMM.

Why can't I set a VLAN ID on my Broadcom network adapter?

Some network adapters will not let you set a VLAN ID if the adapter's configuration does not have a VLAN ID. If you configure the network adapter to use any VLAN ID (other than zero), you should be able to configure any VLAN ID on your virtual network.

What is access mode, and when would I use it?

Access mode restricts the external port of the virtual network to a single VLAN ID. Use access mode when the physical network adapter is connected to a port on the physical network switch that also is in access mode. To give a virtual machine external access on a virtual network that is in access mode, you must configure the virtual machine to use the same VLAN ID as configured in access mode of the virtual network. If the physical network adapter is connected to a port on a physical switch that is in access mode and you do not know the VLAN ID, clear the Enable VLANs on this connection option for the adapter and do not specify a VLAN ID on any of the virtual machines that need external access.

My host has only one physical network adapter. Should I specify a VLAN on the virtual network that the adapter supports?

If you configure a VLAN for the single network connection to the host, you might lose the ability to manage the host because network connectivity might be lost. If you specify a VLAN for the virtual network, ensure that the VMM server can maintain network connectivity after the change is made.

How is a dynamic MAC address created in VMM 2008?

If you choose to use a dynamic MAC address when you configure a new virtual interface card on a virtual machine, the virtualization software of the host assigns a MAC address from its own pool.

Alternatively, you can specify a static MAC address or you can define a range for VMM to use and then have VMM generate new addresses from that range when you create a virtual machine. For more information, see How to Set the Static MAC Address Range for Virtual Network Devices.

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