Windows Server – Change a DHCP Scopes Subnet Mask

KB ID 0001177 


You have probably tried to do this and found he option ‘greyed out’ because in the DHCP management console you can’t change the subnet mask of a scope. 

I needed to change a clients DHCP scope because I was changing their subnet from /24 to /16. I could have simply deleted and recreated the scope, but they has a lot of custom settings for their phone system, and hundreds of reservations (which I know is unusual).


I wrote an article a long time ago about migrating DHCP scopes, this process uses the same method to take a backup of the scope, then you can edit the subnet mask, and ‘re-import’ the scope again.

First take a backup of the scope, open an administrative command window, and run the following command;

netsh dhcp server \\”Server name” scope “scope subnet” dump>c\:dhcp.txt
netsh dhcp server \\Server-DC01 scope dump >c:\temp\dhcp.txt

Server 2012 Export DHCP Scope


Then open the C:\dhcp.txt file, and locate the subnet mask;

windows scope change subnet mask

Edit it accordingly, and save the changes.

windows dhcp change mask


You can now DELETE the live scope, then reimport the one you just edited with the following command;

netsh exec c:\temp\dhcp.txt 

Server 2012 Import DHCP Scope

Note: As you can see even when is has successfully import dyou will still see a “The following command was not found d error

On older, (pre Windows Server 2012 machines) use the following syntax instead;

netsh dhcp server import c:\temp\dhcp.txt all

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Author: PeteLong

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  1. When I run the import command on 2012R2, I get the request is not supported.

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  2. I get the same thing as Miles when running the import on 2012 R2 servers. “The request is not supported.” The dump file is from the same sever. Just trying to edit subnet mask.

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    • There you go, updated for Server 2012 🙂


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  3. My WDS server is on Windows Server 2016 and the second option worked for me
    netsh exec C:\Temp\dhcp.txt

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    • Thanks a lot.
      It worked for me at Windows Server 2016 at last.

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  4. This is very helpful for me, Excellent……… 🙂

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  5. When I run the import command on 2012R2 I get the request The following command was not found: .


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    • Hi Sorry it’s taken me a while to reply, I wanted to run up a 2012 server to make sure the post was still relevant, and the code was correct. The screenshots {above} are new ones I took today, so the procedure still works. Are you running the command window ‘as administrator’? See is UAC turned off, and can you try putting the export file in a sub folder i.e. so it’s NOT on the root of the C Drive.


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  6. You should note that if you have issues importing it, make sure you go back into notepad, do a “save as” with Encoding: ANSI. that option is located in the drop down next to the “Save”.

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  7. Very useful. It worked for me from the first try. I did same few years ago, I remember, but then I used the old syntax (with import)

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  8. This just saved me a bunch of time. Thanks for the great write up!

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  9. No need to change the subnet mask on the router interface?

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    • Yes – and all other statically assigned IP addresses on the network, and possibly any dynamic routing, but the article is specific to DHCP scopes!


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  10. Thank you So much, Excelling work, this really helped save bunch of time.

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  11. Great job with the tutorial, thanks!

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