Network Connections on Server 2008 with Hyper V

Posted on 2009-04-17
Last Modified: 2012-05-06
I have a question about network connection configuration with Hyper V. So here is my scenario: you have a host server with a single virtual server. This leaves you with a physical network connection configured as a virtual switch. You then have a virtual connection for the host server and then a virtual connection inside the virtual server. I can give a static IP to the two virtual connections, one for the host and one for the virtual server. The issue comes when you add a second or third physical card to the server. I have a second virtual server with a static IP but it also creates a second virtual connection for the host server. I don't need a second one and it defaults to picking up dhcp address. I cannot disable it because it corresponds with the virtual server as well. Sorry if this is confusing. I would really like to know the correct configuration for this.
Question by:StephenMcCollum
    LVL 10

    Expert Comment

    You totally have 3 physical NICs, 2 Virtual Machines. What is happening with the second VM? do you want it to connect to a specific Virtual network/Virtual Switch? if so which one?

    There are things that we need to understand:
    1. Virtual NIC (installed inside the VM)
    2. Virtual Network or Virtual Switch (you can create any number and does not necessarily be associated with physical NICs
    3. Physical NICs (we can associate one or more virtual networks to each of them)

    There are three kinds of Virtual Networks:
    1. External (used to connect to your physical NIC to forward the packets outside the hyper v host)
    2. Internal Only (Used to limit communication with in hyper v host
    3. Private VM network (No communication from VMs to the physical host and vice versa

    Just let me know what you need to do and what are you trying to acheive.

    LVL 1

    Author Comment

    Here is my scenario in more visual terms:

    Physical NIC 1 (Virtual Switch) ----> Virtual NIC A ----> Virtual Machine with Virtual NIC 1
    Physical NIC 2 (Virtual Switch) ----> Virtual NIC B ----> Virtual Machine with Virtual NIC 2

    Ok so on the host 2008 machine we see:

    Physical NIC 1 - Local Area Connection 1
    Physical NIC 2 - Local Area Connection 2
    Virtual NIC A - Local Area Connection 3
    Virtual NIC B - Local Area Connection 4

    And then the two virtual machines have Virtual NIC 1 and Virtual NIC 2

    Here is an example of what I want to configure:

    Local Area Connection 1 - TCP unbound (now a virtual switch)
    Local Area Connection 2 - TCP unbound (now a virtual switch)
    Local Area Connection 3 -
    Local Area Connection 4 - ????

    Virtual NIC 1 in virtal machine 1-
    Virtual NIC 2 in virtual machine 2 -

    My whole question is, now what do I do with the extra virtual NIC (Local Area Connection 4) on the host? I do not want multiple IP's on the host do I? It is set as DHCP. If I disable it, then it disables the virtual NIC in virtual machine 2.

    Does this make sense?
    LVL 10

    Expert Comment

    It actually does not disable the NIC on the Virtual machine but stops the communication as you have disabled the virtual switch. So keep it enabled for the VM's traffic to pass. There has to be an adapter associated with the Virtual network if you configured them to be either External or Internal only, it can be a physical or a virtual adapter.

    If you set to use physical adapter, you can forward the packets to outside of the machine and if it is internal, then that adapter acts as a loopback adapter enabling the communication only between the VMs and the host.

    If you dont assign an IP to the Virtual Adapter that got created with the virtual network's name, then the only thing you wont be able to do is to communicate with the host machine, rest all works fine, but dont disable it.

    Any further questions?
    LVL 1

    Author Comment

    You answer makes sense. I am just wondering the best practice to assigning an IP to the Virtual Adapter that got created? It picks up a DHCP address by default. I don't really need any IP in there. It is just using 1 more DHCP address for each network card I add.
    LVL 10

    Expert Comment

    If you are talking about IP assigned by APIPA Service (169.x.x.x) then that is some thing you can ignore. or you can also assign an IP address to that interface. Or just disable the APIPA service for that interface.

    "Start a registry editor and go to the HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters\Interfaces subkey. Select the string that identifies your adapter, and create a new DWORD Value. Name the entry IPAutoconfigurationEnabled, and set the value to 0. If you have multiple adapters, repeat the process for each adapter under the Interfaces subkey."
    LVL 1

    Author Comment

    Not APIPA, it picks up a DHCP address from the DHCP server on the network.
    LVL 10

    Accepted Solution

    you can disable that behavior by following my previous suggestion and also set the value for 'EnableDHCP' to 0.

    Make sure that the changes are being done to the appropriate NIC.

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