Merging and consolidating DHCP Server scopes with different subnet masks to a new scope


  • Hi there,

    I need help on the following issue:


    DHCP migrations from 2 Windows Servers 2003 (AD: Windows Server 2003) to two new W2K 8 Server R2 SP1 servers in a new Domain (AD: W2K8).

     Scopes to be migrated:

    1. From the first legacy server: Server A Windows 2003 Server

     1.1 Scopes: one for the LAN with a subnet: 255.255.00, Length 16

    1.2 Scope: WLAN Scope with subnet mask:, Length 24

    2. From the second  legacy server (W2k3), Server B:

    One scope with a subnet mask of, Length 16

    There is no scope overlapping.

    Also, DHCP fault tolerance must be implemented. This will be done by ‘merging’\consolidating all scopes on each new server.

    Then implementing the split-Scope rule 80/20

    While trying to test this approach on a test server, which does not represent the prod environment as all servers are members of one Domain: W2K8 I got the following results:

    -->Only the scope(s) of one legacy server (Server A, or Server B) can be migrated, but unfortunately not all of scopes on all servers.

    I get the following error when using the migration method: netsh dhcp server Export (Import)


    Error while importing subnet x.x.x.x

    This subnet already exists on the local server


    This error comes up also when migrating or creating the failing subnet manually.


    1. How can I prevent this error message from occurring?
    2. What is the recommended method for merging DHCP scopes with different subnet masks? Is this generally possible?
    3. Does  a Microsoft tool exist, which is able to merge DHCP scopes into one scope?
    4. Are there any Registry tweaks or Powershell scripts that may be used to accomplish this task?
    5. Is the AD the culprit in this case?

    I have searched the net for similar issues and have tried several methods of migration but it still does not work.

    Please help.

    Thank you.









    Tuesday, November 15, 2011 6:53 PM


  • Hi Falke11,

    Thank you for your post.

    1.The error means the import subnet already authorized in domain, you need to unauthorized and stop old DHCP server.
    2.Just use netsh to merging DHCP scope following KB281626
    3.Merge into one scope? Not exist this tool. Just could export and import DHCP address list, but it doesn't make sense.
    4.To move DHCP from Windows 2003 to Windows 2008, suggest you remove scope option first and then follow KB962355.

    If there are more inquiries on this issue, please feel free to let us know.

    Rick Tan

    Friday, November 18, 2011 8:12 AM