KB ID 0001177 

Problem

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).

Solution

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;

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

i.e.
netsh dhcp server \\Server-DC01 scope 10.0.0.0 dump >c:\temp\dhcp.txt

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

Edit it accordingly, and save the changes.

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

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netsh exec c:\temp\dhcp.txt 

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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;

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

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Related Articles, References, Credits, or External Links

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