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I have a D-Link / TP-Link router which is working as DHCP server leasing IP address to IP phones and workstations. I need to replace this with Windows Server 2012 without interrupting the operation of the devices. How this is possible?

  • What is your network's DNS server right now, and what it will be after your Windows Server implementation? – Marco Aug 20 '17 at 11:04
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The risk you have is that the new server assigns the same IP address to a new client while some other device still has a non-expired lease from the old DHCP server. There are several approaches to avoid this:

  • Decrease lease time before the change down to 30 or 60 minutes and do the change overnight. This need to be at least the current lease time in advance.
  • If you have space within the subnet and don't need to use the same pool, pick the new pool from non-overlapping range.
  • List all leases from the old DHCP and add then as static reservations to the new one before starting the service. This option minimizes the risk but possibly makes your DHCP less manageable in the future as you need to manually remove unnecessary reservations (when retiring devices or if you have temporary/foreign devices).
  • If you can say for sure that all devices will connect DHCP if the network goes down, you can reboot all switches right after the change. However, this doesn't fulfill the requirement of no downtime at all.

You know your network and needs better to pick the most suitable alternative.

  • I'd use hint #3, but I would delete all reservations after successful migration. – Marco Aug 20 '17 at 11:03
  • Thanks in advance. DHCP in the D-Link router not sure if it has a lease time. If not then how? – truthtriumphs Aug 21 '17 at 7:36
  • If you can't change it, you need to pick another option. There's four different approaches. – Esa Jokinen Aug 21 '17 at 7:38
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If you don't mind changing the IP addresses you can just configure the scope on 2012 - it won't hand out addresses that are still in use (verified through ARP).

If you don't want to change any of the IP addresses, you can configure an empty(!) scope and add all present addresses to the reservations. That way only the reservations are offered, guaranteeing unchanged addresses. When you're done, shut down the old DHCP server and add a scope for the dynamic pool.

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Setup DHCP and go.

  1. Setup your scopes for your lan
  2. Enable conflict detection on the DHCP server in server 2012.
  3. Turn off DHCP from the router
  4. Authorize and activate the scope on the DHCP on the server.

That's all there is to it. Conflict detection was made for this. You don't have to jump through any of the other hoops.

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You can try the following points to configure the same environment:

  1. First, disable the dhcp from your dlink router so that your workstations/host can get the IP from windows server 2012 dhcp.
  2. Install DHCP role in your windows server
  3. Configure the scope of the ip addresses, lease time, reserved ip, and other details.
  4. Make sure that your windows server is connected to the dlink router directly.
  5. Install router role on your windows server 2012 and you need an extra network adapter to provide connection to the host.
  6. Connect switch to windows server 2012 and now you can distribute the ip from your windows server 2012

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