Hyper-V duplicates host mac address?

Posted on 2011-10-13
Last Modified: 2012-05-12

i have an issue where the phyiscal network adapter mac address is duplicated with virtual network adapter?

i have another hyper-v host on the  network and i have no issues with that?

i have deleted virtual network and re-created it and also purchased a new NIC thinking it could be that - but i get same results with that as well??

please help...
Question by:badabing1
    LVL 20

    Expert Comment

    by:Svet Paperov
    It should not be the case. The first 6 hex numbers in a MAC address represent the NIC manufacture. Hyper-V has its own range, on all my servers it's 00155D. You can change the range in Global settings of Virtual Network Manager
    LVL 15

    Expert Comment

    Are you talking about the Virtual Network on the Host Server or the Virtual Network on the Guest Machine?

    My guess is that you’re talking about the host server. If that’s the case then you shouldn’t worry about the MAC address. I checked it on my test environment and the mac address of the virtual network on the host server is showing up the same as the mac address of physical network. Now this should NOT cause any problems since you won’t be dealing with the physical connection settings in the host and will only need to work with the virtual network adaptor on that server. So unless this is causing you a specific issue, you shouldn’t worry about it.

    On the other hand, as spaperov mentioned above, your NIC on the Guest Servers should not be have the same mac as the host server and their mac should start with 00-11-5D. You can change the MAC address in the Hyper-V manager by right clicking on the Client computer name, Settings, and Network Adaptor. Make sure the client is turned off and change the MAC address from Dynaminc to Static and type it in.



    Author Comment

    Thanks for the replies but im pretty much aware of the concept and MAC changes..


    im talking about virtual network on the host not the guest machines (VM machines MAC's are fine).

    "I checked it on my test environment and the mac address of the virtual network on the host server is showing up the same as the mac address of physical network. Now this should NOT cause any problems since you won’t be dealing with the physical connection settings in the host and will only need to work with the virtual network adaptor on that server"

    not true- it is causing me couple of issues -

    1. if i RDP from my laptop to Hyper-V  it drops connection and its very slow to display anything, freezes -more likely conflict/collision with mac on physical and virtual adapter? however, if RDP to guest machines i get no problems!!

    2. if i try to create another virtual network - i get error saying the physical adapter is already binded (something like that)- from what i read you should be able to create  i think up to 14 network in total? surely im not going to add 14 physical adpaters and bind each virtual network with each physical adapter?

    try creating another virtual network adpater on your Hyper-v...

    p.s how come on my other hyper-v server it isnt duplicated? the physical and vitual adapters have a unique mac addresses- and i can create more network without any issues!!

    is there a hotfix that im missing or something, as im going mad trying to fix this?

    LVL 15

    Accepted Solution

    1. I Suggest troubleshooting the RDP connectivity with the Host machine. You'll find a lot of articles about that specific problem on the net (i.e. Host RDP is unstable, Guest RDP is OK). Also, Microsoft recommends that your Hyper-V server contains a minimum of two network adapters. In this type of configuration, one of the network adapters would be dedicated to your management network (for managing the host server), and the other adapter would be dedicated to your virtual machines.

    If you're only limited to one NIC, then you might want to look at this link here.

    2. Again, that is by design. I tried it on two of my R2 servers and I got the same error message : "Unable to find to 'NIC' because it is already bound to another virtual network. Have a look at the link below:
    ....In the case of private and internal virtual networks, the name of the virtual network needs to be specified together with optional descriptive notes. In the case of external private networks, a physical network adapter must be selected from the drop down list. As previously mentioned, physical network adapters which are already bound to another external network, or that are used for remote administration of the Hyper-V Server cannot be used for other external virtual networks......

    Try running this command on your machine that you say creates different mac addresses and compare the MACs. When I ran it on the 2008 R2 Hyper-V host, it gave me the same MAC address for the physical and virtual network:

    WMIC nicconfig get description,macaddress

    Open in new window

    Vahid Haeri

    Author Comment

    Thanks for your reply-

    i will test the first link tonight - looks good thanks!

    the second is also good and it kind of say's what youinitially said- ill accept that you need one nic per network i have tried this and its throwing up an error! however, the duplication of IP i am still confused with, as you can see i have taken a screen print of my existing Hyper-v and you can see both macs as diffrent?

    the only diffrent between these two pyhsical servers is that they are diffrent makes!

    let me know what you think and then ill assign points to you well deserved for finding a fix!

    Author Closing Comment

    Im happy with the fix found by vahid, but i still didnt get an answer to the mac duplicates. nevertheless, you deserve the points for helping out. Thanks

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