As part of a corporate project, I am responsible for changing the IP address range of remote sites. I will show you a theoretical scheme of the network and explain the details of the migration. My final question will be: should I think of everything and will the network function in an operational way?

enter image description here

This corresponds to the network of my site (in a simplified way). The current network IP address is in 169.x.x.x / 16, and my wish is to switch it to 172.x.x.x / 24 There is in my network, a manageable switch, dynamic IP equipment (computers) or fixed IP equipement (printer, PABX, File Server ...).

Here are some facts:

  • The network is managed by Microsoft tools (AD, SCCM)
  • No changes to be made to the DHCP, DNS servers and the data center(except the new DHCP range)
  • Printers are managed by DNS name, no changes to make for FAX

I am going to share with you an "action-list" that I have written and I hope you will be able to tell me what is good or bad:

  1. Disable the old DHCP scope
  2. Manually change the IP of the file server, domain controller. Then printers, Access Point and other equipment in fixed IP
  3. Change the IP of the switch (from here, the LAN should be able to work)
  4. Change the IP of the LAN interface of the router.
  5. Change the IP range of the firewall ACLs, and SCCM Boundaries

After that, I think we have to wait a few minutes for the tables to update, and the network should work. Do I forget important things that can cause problem after change?

I am available to answer questions to the best of my knowledge.

I apologize for my low level of English, but I have an excuse, I'm French!

  • What kind of connection do you have between the site and the datacenter? Are you running a routing protocol (like OSPF or EIGRP)? You need to take account the routing between those sites. Your English seems fine to me but, hé, I'm french...
    – JFL
    Commented Feb 19, 2018 at 14:38
  • The WAN connection is managed by the ISP. What I am going to do now is to be sure to route on the new subnet so I think this point is OK. Thank you for your help Commented Feb 20, 2018 at 8:06
  • Did any answer help you? If so, you should accept the answer so that the question doesn't keep popping up forever, looking for an answer. Alternatively, you could provide and accept your own answer.
    – Ron Maupin
    Commented Apr 1, 2018 at 21:06

1 Answer 1


Your list sounds reasonable enough for the site itself but don't forget :

  • to decrease the DHCP lease duration before you do the operation (make it something short like 30 minutes, or even less) so that when you update the DHCP settings all the devices move over quickly.
  • to route the new subnet on your WAN, and make sure it is routed explicitely anywhere you had a 169 route previously.
  • to update any firewalls rules which might depend on one of the old IPs, wherever that firewall may be
  • to update Active Directory site/subnet declarations
  • to update endpoint firewall/AV settings as well (sometimes you can have explicit rules)

I would also take this opportunity to make this easier for next time: instead of using fixed IPs for printers (or even APs) give them static DHCP assignments. That way if you ever need to change settings again (a new DNS for example) you'll have a mostly one-stop change to make.

Also, if you're afraid of breaking things or forgetting something, you can configure your router such that it has the new 172 IP as its primary, and the old 169 IP as a secondary IP. That way, any device you've forgotten will still be reachable until you remove the secondary IP. The new IP has to be the primary as that's what's used for DHCP relay (on Cisco HW anyway).

  • Hi Jeremy, thank you for your reply. I'll pay attention to what you told me, your help is very relevant. I was thinking about the secondary address on the router and you conviced me. About DHCP assignement : I'm not sure how it works. Do I simply have to create a new assignement on my DHCP server and the printer will take the IP ? Thank you again for your precious help ! Commented Feb 20, 2018 at 8:12
  • 1
    Yes: your DHCP server should have a means to create a static assignment, i.e. whenever it receives a request for a certain MAC address, it should always return that same IP. The procedure varies from server to server, so it's hard to give you a more precise answer. On Windows it's under your scope, in the Reservations item. Commented Feb 20, 2018 at 8:12
  • Great ! Understand, it's a good choice so. Last question : does it works with lease as a DHCP range ? (so whenever the last lease is over, it will take the new reservation?) Commented Feb 20, 2018 at 8:25
  • Yes, the static assignment is like normal DHCP from the client's perspective, the only difference is it always gets the same IP back. Commented Feb 20, 2018 at 10:46

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.