Renumbering IP Addresses

By Leo Vegoda
April 19, 2022

We refer to the internet services we use with names like but those names hide a layer of numbers. These are internet protocol, or IP, addresses. The most widely deployed version is IPv4. It has a theoretical maximum of about 4.3 billion addresses. Only about 3.8 billion IPv4 addresses are available for use by ordinary internet devices. That means we have about half as many addresses as people on Earth.

An IP address is just a number. People are familiar with IPv4 addresses in “dotted decimal” format. But we could write an address like as 3,325,256,746. We use the dotted decimal format to help us understand quickly and easily where a block (or sequence) of numbers starts and ends.

The Need to Renumber

Blocks of IPv4 addresses used to be assigned in three sizes. The smallest, known as a Class C, contained 256 addresses. The middle size had just over 65,000 addresses and was called a Class B. The largest size had over 16 million addresses and was called a Class A. These dramatically different sizes meant that users were assigned blocks of IP addresses (classes) of very different proportion. What’s more, it resulted in many networks being distributed far more than they needed simply because a smaller block wasn’t enough. Registries gave organizations that needed just a few thousand IPv4 addresses a whole Class B.

Times have changed. IPv4 addresses have significant market value because the registry pools of available addresses have been emptied by ever-growing demand. That heavy use occurred because people have multiple devices. And they use them at home, on the move, and in the office.

Continuously growing demand did not end when the registries’ free pools were emptied. The RIRs introduced policies to support a market where organizations can legitimately exchange IPv4 address blocks. This keeps accurate contact information about network operators available. In 2022, many new organizations and growing cloud services companies are buying IPv4. Prices have risen in recent years and generally more than cover the cost of reassigning an IP address to a new device, a.k.a. “renumbering.”

Renumbering What?

To put it simply, when additional IPv4 addresses are acquired, the devices that will use those addresses must have their identifying IP changed. This change is known as renumbering and, when large numbers of devices are involved, can be time-consuming.

Requirements for Changing IP Address Numbers

Any successful change starts by understanding the current situation. An IP Address Management (IPAM) tool will inventory the IP addresses on your network. You can use this to build a picture of what needs to change.

IPAMs are more than databases recording which addresses are used and where. They can discover where IP addresses are used. You can then use your IPAM as part of your deployment by updating DNS and detecting unauthorized devices.

Then you need to centralize and automate configuration.

Using a configuration management and orchestration system will help you maintain baseline configurations. You can then adjust individual configurations as needed and automate updates. And you can audit configurations and deploy improvements when you centralize configuration management.

Changing Static IP Address Numbers

Organizations are sometimes worried about renumbering because they use static addresses. Some software vendors demand that software be tied to addresses. This is less common now, with online license validation or audits available as alternatives. Where neither of these is offered, it is often possible to use IPv6 addresses instead. 

Building the Plan

Some organizations periodically stop production to perform maintenance on capital equipment. Planning around these situations before starting to renumber is recommended. If that’s not possible, taking an incremental approach might work well. Start with a small segment and get used to the new tools. Then, expand across the whole network in steps.

Stages of Renumbering IP Addresses

Whichever approach is right for your organization, you need to manage renumbering in the following stages:

  • Your connectivity providers need to know to route your new prefix or prefixes.
  • You will need to update DNS names pointing to addresses in the old prefix.
  • You will need to update configurations for systems that interact using addresses instead of DNS names.

It is often possible to introduce a new prefix alongside the old one. You can then remove the old prefix once you have the new one up and running and have tested that traffic is using it. You can remove it when you are sure there are no more dependencies on the old prefix.

Some organizations distribute responsibilities for network, servers, and applications to different teams. If yours does this, then your internal communication will be just as important as the technologies you use. People in different parts of your organization will need to actively cooperate.

Expert IP Renumbering Strategies

You don’t need to develop and execute a plan for renumbering on your own. We can help. Contact us so we can get you the experience you need for your team. We’ll help you do three important things:

  • Improve your network
  • Free up space to bring in revenue
  • Help other organizations achieve their own needs in the process

Read More About Changing IP Address Numbers

The IETF has produced a collection of documents that look at renumbering. While they focus on IPv6 networks, most of what they say applies to any network.

The IPv6 Site Renumbering (6renum) Working Group produced documents on:

  • What problems to solve
  • The scenarios and methods
  • A gap analysis.

The IPv6 Operations (v6ops) Working Group produced a document on how to renumber without a flag day.