Migrating DHCP & DNS first or DCPROMO first from 2008R2 to 2012 R2 ?


I've got two 2008 R2 AD Domain Controller that is running also as Global Catalog in one of my AD site.
It doesn't run any of the FSMO roles, but it is currently serving as AD integrated DNS server and also DHCP server for the subnet.

I have deployed 2x Win 2012 R2 VMs but now I'm confused myself. Should I:

#1 Migrate both DNS and DHCP (I will setup DHCP resiliency in the two new 2012R2) first, then DCPROMO after
#2 DCPROMO the two new 2012 R2 VMs as DC/GC and then migrate both DHCP & DNS server

Which one is better or the most recommended way ?
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Senior IT System EngineerSenior Systems EngineerAsked:
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Patrick BogersDatacenter platform engineer LindowsCommented:

When you promote a DC you can promote the dns role in one action.
DHCP is to be considered a seperate mechanism so it does not matter.
Offcourse Once promoted a new DC and or dns server adjust the dhcp options accordingly.


Free tip: it is to be advised to keep one fysical DC, in case of power faillure it is the box you want up and running first.
Todd NelsonSystems EngineerCommented:
Promote the new servers to DCs first.  This action will install the DNS role and should replicate your existing DNS zones automatically.

Second, I would migrate DHCP.  Install the DHCP Server role on one of the new servers.  Then run the follow commands via PowerShell from the new DHCP server to migrate your entire DHCP configuration.  After the migration, disable "DHCP Server" service on old server and remove the role after a couple of days.

Export-DhcpServer -ComputerName "windows2008server.domain.local" -Leases -File "C:\Temp\exporteddhcp.xml" -Verbose
Import-DhcpServer -ComputerName "windows2012server.domain.local" -Leases -File "C:\Temp\exporteddhcp.xml" -BackupPath "C:\Temp\backup" -Verbose

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Additionally, You will need to update all of the machines with static IPs address settings so they all know of the new DNS servers.  And, you will want to migrate your authoritative time server to the new DC that is the PDC emulator.

Lastly, demote the old DCs.

RECOMMENDED: At least one DC should be a physical server.

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Senior IT System EngineerSenior Systems EngineerAuthor Commented:
Thanks Todd,

So in this case, the two Powershell lines must be executed from the new Win 2012 R2 that has already installed DHCP role ?
or do I have to run it from each respective server ?

Patrick & Todd, this is just the deployment in one of the AD site, while in the main Data Center AD site, I already got one Physical machine running all FSMO roles.
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Todd NelsonSystems EngineerCommented:
Yes, both commands must be run from the new server that has the DHCP Server role installed.
Senior IT System EngineerSenior Systems EngineerAuthor Commented:
Hi Todd,

If I promote the two new servers as Domain Controllers + DNS AD Integrated during the business hours, would there be any outage or interruptions to the existing environment ?
Todd NelsonSystems EngineerCommented:
There shouldn't be with those specific tasks.
Senior IT System EngineerSenior Systems EngineerAuthor Commented:
OK, and lastly,

Do I need to reduce the DHCP lease to just 1 hour the day before the migration to make sure the cutover is quicker from the old server to the new server?
Todd NelsonSystems EngineerCommented:
No.  The purpose of migrating dhcp is so you don't need to do that.
Senior IT System EngineerSenior Systems EngineerAuthor Commented:
Ah I see,

So during the DHCP address lease, the IP is still working on the client, so by the time the lease is expired, the client would look for new IP and hopefully the Active-DHCP server will be answering the IP address request.

Is that correct ?
Todd NelsonSystems EngineerCommented:
Todd NelsonSystems EngineerCommented:
Please reassign majority of the points to Todd for more thorough solution and responses to requester's follow up questions.
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