I work for a non-profit with some slightly more antiquated hardware. We have 3 locations, about 700 devices across them. Right now our locations are set up as:

Location 1 (Main) - /23 with a DHCP server. Range is -

Location 2 - /24 with a DHCP server. Range is -

Location 3 - /24 without a DHCP server. This location has the subnet issued by our ISP and all devices are pointed back to our primary and secondary DNS servers via adapter management (often via scripts).

We are rolling out VoIP at the end of the month and I'm not confident we have the necessary IPs to handle the incoming hardware at Location 1 and Location 2. I'm looking for thoughts on the following:

Moving Location 1 to a /22. This location has a ton of static devices (DVRs, Routers, Printers, reserved leases, most of our servers, etc). This would be quite a bit of work.

Moving Location 2 to a /23. This has fewer static devices and probably wouldn't be as difficult.

Here are my questions / issues that are causing me to be conflicted:

I actually don't know how many open IP addresses we have at Location 1. Unfortunately, my predecessor didn't use reservations, so I have no way to see all of the static devices on the network outside of just..knowing. In addition, the scope was set to only 150 addresses of the potential 512, but it was set in the middle of the subnet and I can't figure out why.

I think it would be nice to have all of the VoIP phones on their own cluster of 256, even if I don't NEED the addresses, maybe I should expand and scope it anyway?

I know that /24 has always been the ideal scenario for a network, but anymore is this really necessary? Does anyone see any issues with /22?

We don't have vLANs and our switches are dummy switches. I've been pushing for managed (or partially managed) switches at the minimum, but they aren't approved yet, so vLANs aren't really an option right now.

A final note, all of our servers are physical devices and not virtualized. Again, working on approval, but hard to come by with tight budget constraints. This means that changes are not easily snapshotted or restored from backup.

Anyone have some thoughts or suggestions on what you would recommend?

  • Issues with a /22 compared to a /24 is the broadcast domain. You want to separate your VOIP from any other traffic.
    – CustomX
    Commented Aug 16, 2018 at 11:13

2 Answers 2


I recently went through a very similar VOIP implementation on a 24-bit subnet that was just about full. We decided to shave a bit off the subnet mask as it was a 10.x.x.0 subnet and we didn't have to deal with changing addresses on static devices, only the subnet mask.

There's really nothing great about 24 bit subnets. The only thing I can really think of it does for you is lets ping sweeps etc. run faster because there's fewer addresses to sweep. A 23 bit subnet has twice as many addresses to sweep but it's still a manageable number.

Speaking of ping sweeps, if you are not currently using nmap or some similar tool, you'll find it very useful for taking inventory of your static addresses. (There are GUI tools available as well, whatever you like.) By comparing active DHCP leases and sweeps, you can get a handle on your static devices.

It may help to manage things if you create reservations for all your static devices. This doesn't save you any work, but it lets you chip away at your work rather than having a long night or weekend to cut over. You can create reservations with the 23 bit mask, then on cutover day just change the subnet mask assignment in the scope, cycle power on the switch, and everything comes up with the new subnet.

One thing that might be helpful. Let's say you change the subnet from to So you change the config of the router port, and the DHCP scope. DHCP devices are fine. But static IP devices don't lose all connectivity. In fact the devices configured with static IPs in the OLD RANGE and OLD SUBNET will be able to communicate with devices in the OLD RANGE that are configured with the NEW SUBNET. SO, say you have only phones and VOIP stuff in the NEW part of the range - the OLD static IP stuff, printers, DVRs, etc., may not NEED to communicate with anything in the NEW range. So you can take your time with that.

Regarding QOS and VLANs - this may be controversial but IME on reasonably small subnets like this, with decent gigabit switch hardware, you don't need it. It's main purpose is to prevent VOIP vendors from pointing the finger at LAN congestion to wiggle out of dealing with performance / quality issues.

  • batsplaterson, this is great information! I really appreciate the input. I didn't even think about the old subnet / new subnet communication piece, that will really help with buying me some extra time. I will also certainly start creating reservations as we go through the devices to make this easier going forward. In terms of QoS, we do plan to increase FIA speed 4-fold (a needed change anyway) so hopefully we don't have much issue out the gate, but i'd like to get it done eventually.
    – ct253704
    Commented Aug 15, 2018 at 12:35

The lack of VLANs probably also means the lack of QoS. In that case you may find you get poor voice quality and your project may not be successful. You really need to upgrade your hardware.

But to answer your question, the only issue with changing the IP ranges is that you have to touch every static device. But other than that, any scheme that makes sense to you will work.

  • I did get approved this morning for 7k to spend on switches. However, i need to get 7x 48 port switches and 6x 24 port switches and that price point is tight. Any suggestions on Hardware? I was thinking maybe something like HP 2530 Layer 2 PoE switches or something similar.
    – ct253704
    Commented Aug 15, 2018 at 12:40
  • Sadly, hardware and software recommendations are off-topic
    – Ron Trunk
    Commented Aug 15, 2018 at 12:52
  • @ct253704, the 2530 Aruba switch should be sufficient. Also what AP are you using?
    – CustomX
    Commented Aug 16, 2018 at 11:14

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