Companies that hold Class B IPv4 address space (historically defined as 128.0.0.0 to 191.255.255.255) often face unique challenges in today’s internet landscape. While Class B allocations originally provided up to 65,536 IP addresses, modern network demands, IPv4 scarcity, and evolving policies mean that organizations must rethink how they use, expand, or restructure their Class B resources.
Whether your company still operates a legacy Class B block or needs additional IPv4 space to support growth, there are multiple solutions available in 2025. This guide explores the best IPv4 strategies for companies with Class B addresses, including optimization, expansion, buying, selling, and leasing.
Understanding Class B IPv4 Addresses in Today’s Market
What are the different types of IP addresses, and what makes Class B different?
IP addresses are split into five groups: Class A, B, C, D, and E. The group depends on the size of the network and what the address is used for. Every class has its own range and capacity:
Class A: These addresses are made for very large companies and can handle millions of hosts on one network.
Class B: Best for medium to large networks, like those used by big companies or universities. (Learn more top sand tools for managing large networks with the right tools). Class B blocks have up to 65,536 addresses, which is a good number for operations that need flexibility but not the huge size of Class A.
Class C: These are better for smaller networks because they have fewer addresses per block, but they are easier to manage and give out in bulk.
Class D and E are only used for multicast and experimental purposes, not for standard device addressing.
What makes Class B different is that it strikes a good balance between size and ease of use. In the early days of the internet, companies like IBM, MIT, and regional ISPs used Class B space to power their networks. Class A was too much and Class C was too little. This historical allocation helps keep Class B IPv4 space valuable and strategically important today.
In the early days of the internet, universities, businesses, government agencies, and tech companies were given Class B networks. These blocks were very useful because they gave you a lot of address space that you could change.
Class B IP addresses were perfect for places that needed more addresses than a normal Class C block could give, but not as many as a Class A block could give. For instance:
Schools and colleges often used Class B networks to connect several departments, research labs, and student dorms to the same routing domain.
Corporate Networks: Medium to large businesses used these blocks to support thousands of employee devices, internal servers, and the growing number of IoT technologies.
Government Agencies: Class B ranges were used by municipal and state-level networks because they had a lot of addresses that could be used for many different things, from administrative offices to public services.
The original classful system is no longer used, but the way organizations manage their address space is still influenced by these early Class B assignments.
Public vs. Private Key Differences Between Class B IP Addresses
When looking at Class B IPv4 addresses, it’s important to know the difference between public and private address space. This difference affects how businesses build their networks.
The range of Private Class B addresses is from 172.16.0.0 to 172.31.255.255. These addresses are only for use within organizations. These IPs can’t be seen or routed on the public internet, so they are great for corporate networks, campus settings, or data centers where devices need to talk to each other safely and quickly behind firewalls or NAT devices.
Public Class B addresses, on the other hand, use all of the ranges in the 128.0.0.0 to 191.255.255.255 range except for the private one. These are unique around the world and can be routed over the internet. This lets businesses offer services or connect devices that need to talk to the outside world through their own firewall.
In short, private Class B addresses let companies grow their internal networks without using up the few public IP addresses that are available around the world. Public Class B blocks are still useful for any business that needs a unique online presence.
What is the range of private addresses for Class B?
You can’t use every Class B IP address on the public internet. RFC 1918 says that a certain range of IP addresses, from 172.16.0.0 to 172.31.255.255, is only for private use. These addresses are an important part of business networks, university campuses, and enterprise environments. They are the backbone of everything from simple office LANs to large, multi-site VPNs.
This private Class B range lets businesses grow their internal networks without using up globally routable IPs, which is a big deal since IPv4 is hard to come by these days.
What is the default subnet mask for a Class B IP address?
The standard subnet mask for a Class B IP address is 255.255.0.0. You can also write it as /16. In real life, this means that the first two octets of the address are used to identify the network, and the last two octets are used to identify hosts on that network. This structure let companies manage up to 65,534 usable IP addresses per Class B block. This was a lot at the time, but most of the time, companies don’t need that many.
How to Tell the Network and Host Parts of a Class B IP Address
To tell the difference between the network and host parts, Class B IPv4 addresses have a certain structure. A Class B address usually falls between 128.0.0.0 and 191.255.255.255. In these places:
The first two octets (for example, “172.16” in “172.16”) identify the network part. This part is used to find the whole network on the global Internet.
The last two octets (in our example, “0.1”) tell you what the host part is. This lets businesses give each device on that network its own unique address.
This design provided early adopters—think Stanford University or IBM—with the flexibility to accommodate thousands of hosts while making routing manageable during the formative years of the Internet. Class B’s structure was a good balance between scalability and simplicity, which is what medium-to-large businesses that are growing need.
What does a Class B IP address look like?
Let’s take a quick look at how Class B blocks are made so we can understand why they were so valuable. An IPv4 address in Class B is usually between 128.0.0.0 and 191.255.255.255. This address format has four dotted decimal numbers, like 172.16.0.1.
This is the most important part:
The leftmost numbers, which are the first two octets, tell you what network it is.
The last two octets are set aside for each device, or host, on that network.
With this setup, businesses could support tens of thousands of devices in different departments or locations. Class B was perfect for big universities, Fortune 500 companies, and government agencies that needed room to grow without running out of IPs. It was more flexible than a Class A network but much more generous than a Class C network.
However, today:
- The original classful system is obsolete.
- Routing is classless (CIDR-based).
- IPv4 scarcity has made Class B ranges highly valuable.
- Many organizations no longer need their entire allocation.
- Companies with legacy Class B blocks may be sitting on assets worth millions.
Because modern infrastructure is designed using CIDR, Class B blocks are typically broken into /16, /17, /18, and smaller subnet ranges depending on business needs.
1. Optimize or Reallocate Your Existing Class B Space
If your company has a Class B legacy block, the best and often cheapest thing to do is to make the most of that space.
Why Class B Optimization Is Important
It’s important to know what your Class B IPv4 address space can really do. These addresses were made to find a balance between capacity and ease of use, which makes them perfect for businesses that need a lot of networking. But a lot of companies today realize that their needs have changed, and a lot of the money they set aside isn’t being used or isn’t being used enough.
Careful planning and evaluation of your Class B resources can help make sure that your connection stays up and that you are getting the most out of a valuable asset.
Subnetting in the modern world
It helps to make sure that a Class B block is used efficiently by breaking it up into smaller CIDR ranges.
Getting back unused subnets
A lot of older networks have whole parts that aren’t being used or are being used incorrectly.
Moving to new routing tools
Newer systems are better at handling traffic, keeping it safe, and managing IPs.
Audits within the company
Find out how much of your Class B space is being used, saved, or wasted.
A lot of businesses find that they are only using a small part of their Class B allocation. This gives them the chance to lease or sell ranges that they aren’t using. You can make the most of your address space by carefully thinking about your current and future networking needs. This will free up resources and give your business the most value.
2. Lease Out Unused Class B IPv4 for Monthly Revenue
If you hold more IPv4 than you need, leasing is a powerful solution that turns unused IPs into consistent profit.
Benefits of leasing Class B space:
- Recurring monthly income
- Retain ownership of your legacy block.
- No need for permanent transfer
- High demand from hosting providers and VPN services
- Easy management through a trusted IPv4 broker
A Class B /16 block contains 65,536 addresses, meaning even partial leasing can generate substantial revenue.
3. Sell Unused Class B IPv4 Blocks for Major Profit
Because IPv4 scarcity is increasing, Class B address blocks sell at premium prices. Blocks with clean reputation and correct documentation are among the highest-valued assets in the IPv4 market.
Selling unused ranges enables companies to:
- Unlock significant capital
- Fund modernization or cloud migration
- Eliminate maintenance and compliance overhead.
- Increase operational efficiency
4. Buy Additional IPv4 Space to Support Growth
Some companies with Class B blocks still require more IPv4 due to:
- New services or applications
- Customer expansion
- Multi-region deployments
- SaaS platform scaling
- Datacenter or cloud infrastructure growth
If your Class B space cannot support long-term expansion, buying additional IPv4 blocks is the most stable solution.
IPv4 Hub offers verified, clean IPv4 ranges of all sizes, including:
- /24 for small deployments
- /23, /22 for medium networks
- /21 to /18 for scaling infrastructures
All purchases include blacklist checking, seller verification, and RIR-compliant transfers.
5. Use NAT and IPv6 Integration for Sustainability
Even companies with Class B addresses benefit from hybrid solutions:
Network Address Translation (NAT)
Allows many internal devices to share fewer public IPs.
Dual-stack IPv4 + IPv6 deployments
Ensures compatibility and future-proofing.
Gradual IPv6 migration plans
Reduces long-term reliance on IPv4.
These strategies help maximize your Class B usage and reduce pressure to acquire additional blocks.
6. Protect Your Class B Assets with Proper Management
Large IPv4 holdings require professional care:
- Keep WHOIS records accurate.
- Monitor block reputation regularly.
- Secure routing announcements (RPKI/IRR)
- Use geolocation correction tools.
- Work with reputable brokers for all transactions.
IPv4 Hub provides reputation checks, routing guidance, and secure management support.
Class B IPv4 Blocks Are Valuable. Use Them Wisely
Companies holding Class B IPv4 address space are in a powerful position. These legacy blocks provide flexibility, financial opportunity, and network stability. But they must be managed strategically.
Whether you want to scale your infrastructure, lease unused space, sell for profit, or acquire more IPv4, IPv4 Hub delivers the tools, guidance, and security you need to maximize the value of your assets.