New IP's needed ASAP

We have acquired a new company and we're looking to bring them onto our network. We have a major problem our internal IP's subnets conflict with one another. We must change all of the IP's at one of the companies. I created new subnets but now I need a step by step how to and get them all switched over ASAP. Any suggestions will be appreciated.

Windows 2012r2 Active directory domain.

600 devices, switches, printers, laptops, desktops, servers etc.

1) DHCP - Create new Scopes on the DHCP server, but don't enable them yet.
2) ?
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Qlemo"Batchelor", Developer and EE Topic AdvisorCommented:
The default gateway should be able to have two IP addresses on the same interface, one of each​ subnet. That way all devices are still able to communicate (via the router) no matter if they are already using new IPs.

Unless you go to each DHCP client and force an ipconfig /renew, you do not have much of control over the reallocation process. Your only choice then is to disable the old pool, and trust in DHCP rejecting requests for old IPs. That works fine with machines getting rebooted daily.

Static IPs need to be changed manually, of course.

Firewall rules might have to be adjusted to allow both subnets (both on the main firewall and Windows, if active).

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Natty GregIn Theory (IT)Commented:
Here is a simple guide to replace the scope on a 2012 server

How to Easily change a DHCP's Scope Subnet
When the subnet changes, you will have to do a lot of work to remake all your DHCP's options because you have to erase the scope to remake it after.

You will need to save this information in order to remake:
Excluded IPs
DHCP's scope option(s)

There is a easy way to do it with NETSH;

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

After; edit the file, and change the line;

Dhcp Server \\server add scope "Pool DHCP" ""

Save the file, and when ready erase the DHCP scope and issue netsh exec c:\dhcp.txt

And voila, the scope will be changed easily!

taken from here
Natty GregIn Theory (IT)Commented:
Objection please award the points evenly or delete the question, on the basis that your answer is not the only way to get the job done.
Natty GregIn Theory (IT)Commented:
Just so you know, copy and paste requires work, you also must research, read and make sure the info is relevant to the topic, that is being discussed.

So you can show some appreciation other than being very dismissive.

Time and effort went in.
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