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Physical to Virtual - IP Address Conflict

    Question

  • Hi, I have a physical 2003 R2 server that I am attempting to virtualise onto a 2008 R2 Hyper-V host. The host has its own dedicated NIC (172.16.0.17), a 2nd NIC dedicated to another 2003 guest VM (running fine with 172.16.0.9 on an virtual switch connected to an "External" network) and a 3rd NIC dedicated to the new guest VM (which will be 172.16.0.8 on another virtual switch connected to an "External" network).

    I have used ShadowProtect to back up the physical server (VSS snapshot process) then restore into the new guest VM. I have succesfully used this process several times before. When you bring up the guest for the first time (after switching off the old physical server) you do it in Safe Mode with Networking so you can unhide then uninstall the old physical NIC and therefore release the IP address (172.16.0.8). You can then reboot and set the IP address of the guest's new LAN connection (with the VM Bus Network Adaptor) to the old physical server's address.

    As soon as I do this I get an IP address conflict. The Event Log gives the MAC address of the old physical server's NIC but it has been switched off by this point! I am positive there is no other device on the network with this address. If I change the guest VM's address to something else the message goes away. A ping of 172.16.0.8 produces no reply (no reply on other servers as well). There is no entry in the ARP table for 172.16.0.8. If I show hidden devices in Device Manager the old physical NIC is not there. Devcon only shows the VM Bus Network Adaptor and there are no additonal adaptors in the usual registry locations.

    Curiously if I change the virtual switch to "Private Virtual Machine Network" mode then set the VM guest's IP to 172.16.0.8 there is no conflict message. This implies that the address is in use somewhere on the network but I am sure it isn't.

    Any ideas? Thanks,

    Guy Ellingham

    Friday, November 16, 2012 2:41 AM

Answers

  • Hi Lawrence,

    Thanks for the reply. In the first attempt, before setting up networking in the newly virtualised server, I uninstalled the old NIC, assuming I would be removing any remnants of the old physical MAC and IP addresses. The MAC address supplied for the new virtual network adaptor was a Microsoft 00-15-5D Hyper-V one and I then attempted to bind 172.16.0.8 to it. As soon as I did this I received an IP address conflict error saying 172.16.0.8 was already in use on MAC 00-04-23..., the MAC address of the physical NIC in the old server, ... which had been shut down!

    I worked around the problem in a second attempt by backing up the physical server then changing the IP address to something way out of our scope before shutting it down. I then performed exactly the same VM setup steps as the first time. When the IP address was set on the virtual network adaptor there was no IP conflict message and it has been running sweetly since.

    Weird. The only thing I can think of is that in the first attempt, although the old server was shut down, it wasn't powered off and the network cable was still plugged in. The NIC lights were on and perhaps the MAC wasn't fully "gone". Seems a bit tenous though.

    Anyway, onwards.

    Cheers,
    Guy

    Friday, November 23, 2012 2:45 AM

All replies

  • Hi,

    > I have used ShadowProtect to back up the physical server (VSS snapshot process) then restore into the new guest VM. I have
    > succesfully used this process several times before.

    It’s the same mechanism of Disk2VHD.

    You may uninstall that Virtual network adapter in Virtual Machine, and then reinstall it. This operation will assign new MAC address for the adapter.

    If issue still occurs, you may manually modify MAC address for the virtual machine adapter.

    Run “ipconfig /all” to acquire current MAC

    We assume it is: 00-15-5D-3C-D1-02

     You can modify it in Device Manager--> locate to the virtual machine adapter--> right click, Properties--> Advanced --> Network address --> Value, you can slightly modify it to 00-15-5D-3C-D1-0A

    For more information please refer to following MS articles:

    Hyper-V: MAC Address allocation and apparent network issues MAC collisions can cause
    http://blogs.technet.com/b/jhoward/archive/2008/07/15/hyper-v-mac-address-allocation-and-apparent-network-issues-mac-collisions-can-cause.aspx

    How To Get the MAC Address for an Ethernet Adapter
    http://support.microsoft.com/kb/118623


    Lawrence

    TechNet Community Support

    Monday, November 19, 2012 8:43 AM
    Moderator
  • Hi Lawrence,

    Thanks for the reply. In the first attempt, before setting up networking in the newly virtualised server, I uninstalled the old NIC, assuming I would be removing any remnants of the old physical MAC and IP addresses. The MAC address supplied for the new virtual network adaptor was a Microsoft 00-15-5D Hyper-V one and I then attempted to bind 172.16.0.8 to it. As soon as I did this I received an IP address conflict error saying 172.16.0.8 was already in use on MAC 00-04-23..., the MAC address of the physical NIC in the old server, ... which had been shut down!

    I worked around the problem in a second attempt by backing up the physical server then changing the IP address to something way out of our scope before shutting it down. I then performed exactly the same VM setup steps as the first time. When the IP address was set on the virtual network adaptor there was no IP conflict message and it has been running sweetly since.

    Weird. The only thing I can think of is that in the first attempt, although the old server was shut down, it wasn't powered off and the network cable was still plugged in. The NIC lights were on and perhaps the MAC wasn't fully "gone". Seems a bit tenous though.

    Anyway, onwards.

    Cheers,
    Guy

    Friday, November 23, 2012 2:45 AM
  • Hi,

    After your remind I really remember that after we shut down a server its NIC light is still on.

    So have your tried to unplug the network cable before you shut down the physical server, what the result?


    Lawrence

    TechNet Community Support


    Thursday, November 29, 2012 8:35 AM
    Moderator