Resubnetting Question

Hello, Experts:

Our current network is beginning to run out of IP addresses. We use to with a subnet mask of I would like to change to subnet mask to and came across the following link to do this without having to do a lot of manual changes ( on the DHCP server (Windows Server2008). I am assuming that after I make the change on the DHCP server, I will need to manually change the subnet masks on any devices that have static IPs. What would be the best order to make those chnages? Servers, then switches/routers, then printers, etc. Should I first change the devices and then make the change in DHCP? Thank you.
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I would do Server and Routers at the same time, then switch then hosts.

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Thomas GrassiSystems AdministratorCommented:
I would start with the Router then any other device that has a static ip address
Best to be able to configure them all using the web interface.

If you have many devices

The best is to do one at a time to make sure every thing is ok.

Then all the DHCP devices just need to do and ipconfig /release ipconfig /renew or just restart.
Also keep in mind that during this change, everything currently in the /24 will still be able to communicate, it is when the local host detects that a host it outside of its locally configure network that it will send to the default gateway
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ctsuhakoAuthor Commented:
Thank you for all the comments. Just for final clarification, I should make all the manual changes to the static devices before changing the IP scope and subnet?
You can do either Static devices or Dynamic, whichever you prefer.  I would do static first, as they should still be reachable as long as the IP's dont change.

This way you have time to go around changing them, then you can easily change scope afterwards.

Good luck,

mccarlIT Business Systems Analyst / Software DeveloperCommented:
Firstly, I want to say this... as long as all your IP address initially stay within the existing range, then it doesn't really matter what order you change the subnet masks. Why? Because any host in the range - with either of those subnet masks will communicate perfectly fine with any other host in the IP range and also with either subnet mask. THEN, once all the subnet masks are set in every host, static AND dynamic, then you can have hosts with IP's in the extended range and they will be able to communicate with any other host with no problem. Therefore, this is the order that I would do things...

- Change the subnet masks on the static IP hosts, it really doesn't matter which order but personally, I would probably start with the least critical devices firsts (maybe printers) just to make sure there are no issues, and then do servers, and switches/routers last.

- Then I would change JUST the subnet mask in the DHCP configuration, ie. don't expand the IP range just yet. Let these updates filter out to all the dynamically assigned hosts first.

- Only then, change the IP range to the newly expanded values.

Doing the DHCP change in 2 separate steps means that you don't have the case where say one host gets the updated mask and takes a new address above but then cannot communicate with an existing host that hasn't received any update yet and so is still using the old subnet mask.

Just have to point out one thing though... You said this,
Our current network is beginning to run out of IP addresses
Is that because you have more than (or close to) 254 devices or do you just have a large amount of temporary devices that are using up the IP allocation but not always present?

If it is the first reason (more than 254 devices) you really should be looking at physically subnetting your network. If you just start adding more devices and they are all on the same subnet, then your network performance may suffer. This is because your subnet is also your broadcast domain, meaning that a broadcast packet sent by any device goes to EVERY other device in your subnet
Thomas GrassiSystems AdministratorCommented:
Yes you can just document everything so you have a record of what you changed we like to create a spreadsheet columns before and after good idea.

Good luck
ctsuhakoAuthor Commented:

We are close to running out of IPs for devices (have about 25 IPs left) and they are not temporary. I do not know enough about physically subnetting the network. Do you have any suggestions on good informational sites that I could examine? Thank you!
Thomas GrassiSystems AdministratorCommented:
here is an online subnet calculator
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Windows Server 2008

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