1

DHCP.png

Hey Spiceheads,

Quick question, I’d like to change my DHCP Scope Address Pools, from the above picture you can see my current layout on the left and the new one I’d like to adopt on the right. Moving the static addresses is already done but I don’t know to proceed with 2 dynamic pools - I mean I can easily delete and recreate but what happens to all the dynamics already with addresses? I don’t have to reboot every machine to get a new IP and if I did how would I prevent conflicts? the new scope wouldn’t know anything about the old scopes leases?

7 Spice ups
2

If you’re using a windows based DHCP server, just delete the old scopes and create new ones. Enable conflict detection on the server or scope (don’t remember where that setting is now). The DHCP server will ping an address before it offers an address.

Also, if you’re running 2012+, scrap the separate scopes for separate servers; you can configure dHCP to be highly available on the same scope starting with 2012.

2 Spice ups
3

I’d just stay late one night. Shut everything down, so it releases the addresses. Deactivate the old scopes and activate the new ones. Then boot everything back up. That is unless you are running 24 hour a day operations on with your DHCP clients.

4

Also, also, you wouldn’t have to reboot each workstation to get a new address, use psexec or PowerShell’s Invoke-Commamd to run "ipconfig /release && ipconfig /renew " remotely on the workstations.

Its probably a one or two line batch or ps1 script - or you could even do it without the script.

5

Another option is to lower your lease time way down, wait for all the clients to renew their leases with the short time. Then switch the scopes over. Then raise the lease time back up.

1 Spice up
6

I didn’t even know there was conflict detection. The things you miss sometimes. Anyway I was curious, so I looked for it. It is under IPv4 props, Advanced tab.

7

If I’m not mistaken you can also you reservations so you can switch over that way also.

8

feel free to explain that, right now I’m at the mercy that the DHCP “automagically” pings IPs before assigning them and hoping for the best. it’s 2003 DCs, I plan to make it a high availability in 2008 but that at a later date.

9

Making reservations is a pain in 2003 - if I remember right. Not to mention, you’d have to manually make the same reservation on both of your DHCP servers, just in case.

10

But you can use info from this article to slightly automate the process, once you’ve created a csv of all ip addresses, mac addresses and computernames: http://retrohack.com/creating-dhcp-reservations-at-the-command-line/

1 Spice up
11

With the new scope you would set a reservation with all of your PC’s. When you are ready to switch over ask them to power down the night before that will release the IP’s and force it to the new reservation once it is restarted. The shut down will stop the conflicting of IP’s.

12

If you’re just going to have the clients shut off the PCs, then don’t bother with the reservations. The clients will re-request an IP from the DHCP servers when they startup again, and they’ll get new IPs in the new scope - no conflict.

13

I only suggested that because when we did that in my company a couple of PC’s were still pulling from the old scope that we were switching them from. I’m saying you are right on this I just thought the reservation would be easier and better.

14

We are in the planning process of re doing the dhcp scope with a larger subnet. However, my boss is thinking that if we delete the old scope and recreate the scope with new addressing that dns and active directory is going to shut down and nothing is going to work. Does anyone know what other ramifications there could be other than possible ip conflicts? Is dns going to just stop working?

15

DNS will not stop working; you may need to create additional reverse lookup zones.

AD does not depend upon DHCP, only DNS. As long as the DNS servers are setup correctly in the DHCP scope, you should be okay.

16

just a quick update on this;
the Address Pool change went off without a single hitch, pretty much happens “automagically” and I was worried for nothing - deleted Scopes, made new ones - within the hour all the PCs had registered within the new pool

literally easy peasy lemon squeezy

3 Spice ups