Reuse old domain controller IP address

Question

We currently have 2 Windows Server 2008 R2 domain controllers, and I want to replace one of them with a Server 2012 R2 DC. I also want to reuse the IP address after I demote the old DC.

What is the best way to do this and will reusing the old IP cause any problems?

Solution 1

• Build the new server
• Give it a temporary IP address
• Join it to the domain
• Promote it to DC (you could need some adprep if this hasn't already been done)
• Add required additional services (DNS, etc.)
• Move FSMO roles if required
• Change the IP address of the old DC to a temporary one
• Reboot the old DC two times
• Wait some time for replication (an hour should be more than enough)
• Give the IP address of the old DC to the new DC
• Reboot the new DC two times
• Wait some time for replication (an hour should be more than enough)
• Demote the old DC
• Leave the old DC in service if there are more data or services on it, otherwise just shut it down.

Solution 2

"Best" is highly subjective, but you can re-use the same IP address after you demote the domain controller. You just need to make sure that the references to the old domain controller are gone from Active Directory before promoting a new domain controller at that IP address, and keep in mind that client computers may need to reboot (or at least refresh their network connection) if they have any cached/inactive sessions with the old domain controller.

And, no, it doesn't cause any problems. I've done it myself many, many times myself when I don't want to go through the hassle of updating manually-configured DNS server records on a whole bunch of computers.

Comments

[HopelessN00b]

Why not just demote the old DC, wait for replication, and promote a new one at its old IP address?

[Ryan Horan]

Thanks Massimo that was an awesome answer! short and to the point.

[gravyface]

@Massimo what would happen if the old DCs are not demoted/decommissioned, but given new IP addresses, and the old IPs assigned to new DCs? Would save having to change DNS IPs everywhere.

[Massimo]

@gravyface I don't understand your comment; the plan already is to reuse the same IP address for the new DC, probably for this exact reason (avoid DNS changes). Anyway, after you give the old DC a different IP address, you can leave it in service as long as you wish.

[gravyface]

@Massimo I'm just curious as to the behavior in a scenario where you don't remove the old DCs, but re-use their IPs for the new DCs, and give the old DCs new IP addresses, with the ideal that you'd demote/decom the old DCs at a later date.

[gravyface]

(2/2) from what I've read, you need to make sure that ntdsutil has no references to the old DCs if you want to re-use hostnames, but wasn't sure if there would be any stale DNS issues where a DC thinks it's replicating to DC1, but instead, is replicating to DC3, which now has DC1's old IP address.

[gravyface]

@Massimo disregard. xmas hangover, fog has not lifted. As you were. :)