Best practice for shutting down old DHCP server on windows server 2008 and set up new dhcp on windows server 2012

I had this question after viewing Removing DHCP Server and Clients are not getting address from new server i've installed..


I am getting ready to shut down a server running windows server 2008 with dns, dhcp, etc.  I am going to completely get rid of this server.  I have a new Windows 2012 server set up with DNS, and is now the primary domain controller within the network.  The only service it is not running is dhcp.  I want to set up an entirely new scope on the new server.  (I inherited the old one and it was set up with a 20. range.)  I was told I should change to the 10. (private network) range.

What is the best way to go about this?
manch03Asked:
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Mal OsborneAlpha GeekCommented:
There are 3 "reserved" IP address ranges, intended for "private" networks behind a NAT device:

10.0.0.0 – 10.255.255.255,
172.16.0.0 – 172.31.255.255
192.168.0.0 – 192.168.255.255

Nearly always, your internal workstations should be using addresses within that range. Assuming you have less than about 100 machines, any class C network with a 255.255.255.0 mask is a good choice.

Changing an IP range is not rocket science, but  can be a little tricky, here are a few pointers:
1. Windows, by default uses an 8 day DHCP lease. This means that a machine can keep its old IP for over a week. Before going any further, reduce the lease time. I would go for one hour.  Machines will get a new lease time after their lease is half expired, so 4 days by default.
2. You will need to change the IP addressing an ALL devices, servers, printers, routers, WAPs  etc. I would advise using some sort of software that can scan the subnet and see what IPs are in use, just so you can ensure everything has been identified. I would use Advanced IP scanner, http://www.advanced-ip-scanner.com but there are many others.
3. Other than that, it is pretty straightforward. I would probably make this change early one morning, before users log in. The day before, make sure you have passwords and can access all devices. On the morning, change the servers ect, create a new DHCP scope, then let the client PCs pick up a new address via DHCP.
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Lionel MMSmall Business IT ConsultantCommented:
Once you have migrated all the roles and setup the new DHCP it simply turning the old DHCP server off; the existing devices on the network should "search" for a DHCP, will start by the IP known before and if not found keep looking until it finds the next one. I usually shutdown the old server and test to make sure all works as desired with it off and if not I can turn it back on and make more changes until everything works with the old on off and only then finally remove it -- hope that helps?
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Eugene ZCommented:
I'd follow MSFT best practice,

check this MSFT guide
Migrate DHCP Server to Windows Server 2012 R2
https://technet.microsoft.com/en-us/library/dn495425(v=ws.11).aspx
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Lionel MMSmall Business IT ConsultantCommented:
I hope this conclusion to this question is acceptable to everyone--if not let me know.
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